Gallium Nitride (GaN)-based High Electron Mobility Transistor (HEMT) technology is revolutionizing the modern defence RF and electronic warfare systems. The capability of AlGaN/GaN HEMT to deliver high power, high frequency, high linearity, high efficiency and high temperature performance renders it the most sought after device for applications in advanced radars, data links, satcoms, etc. Particularly for RF power applications, GaN-based HEMT technology offers a significant advantage over the existing gallium arsenide (GaAs) Monolithic Microwave Integrated Circuits (MMICs). This is primarily due to the capability of GaN devices to operate at higher voltages owing to very high breakdown fields associated with them. Additionally, the GaN devices offer much higher impedance resulting in the requirement of less complex matching networks in RF power amplifier integrated circuits. On the whole, GaN technology results in minimizing the sizes of RF ICs by a factor of ten or even higher over the competing RF technologies. Moreover, the low current operation aided with a higher efficiency results in power saving and reduced costs for cooling the system. Therefore, the GaN-based power amplifiers constitute the heart of present day transceiver (T/R) modules in AESA (Active Electronically Scanned Array) radars and communication systems. To harness the potential of this technology, a project entitled AlGaN/GaN High Electron Mobility Transistors: Material and Device Technology Development (BALRAM) was undertaken by Solid State Physics Laboratory (SSPL) as a first step towards achieving long term self-reliance in GaN-based material, high power devices/MMICs for RF applications. SSPL evolved process control and characterization methodologies, besides, timely development of facilities for (a) epi-wafer growth and characterization, (b) device simulation, (c) device fabrication and (d) DC, RF and load pull measurement etc.
EPI-Wafer Growth Technology
AlGaN/GaN hetero-structures having a two dimensional (2D) electron gas with a high electron density of ~1013 cm-2 and electron mobility of ~2000 cm-2 V-1s-1 are required for fabrication of high performance HEMT devices. A typical GaN HEMT hetero-structures consists of a multilayer hetero-epitaxial structure with strict control over composition as well as thicknesses at nanometer scale. The desired smoothness/abruptness of various interfaces at sub-nanometer level requires atomic scale control over growth process. Metal Organic Chemical Vapour Deposition (MDCVD) was selected for developing AlGaN/GaN HEMT epi-wafer growth process for its capability of scaling up for volume production and low manufacturing cost. A specially designed MOCVD reactor was established and a production worthy GaN HEMT epi-wafer growth technology was developed with sustained R&D efforts. A variety of crystalline substrate options, namely, Sapphire, SiC and Si, were explored for growing the desired epitaxial hetero-structures. However, the technology development was finally confined on SiC due to its least mismatch in lattice constant and thermal expansion coefficient with GaN. Further, a high thermal conductivity of SiC renders it most suitable for high power RF applications. The main challenges in developing the GaN HEMT material technology included achieving the desired 2D electron density and mobility with reduced dislocation density and control over impurities acting as deep electron traps. Other crucial requirements for AlGaN/GaN HEMT structure included (a) the growth of high resistivity GaN buffer layer, (b) precisely controlled 1 nm AlN exclusion layer with sharp interfaces and (c) growth of crack free AlGaN layers with step flow morphology while maintaining minimum particulate generation during growth. The indigenous GaN HEMT materials technology is matured and device quality epi-wafers are regularly produced for fabrication of Power HEMT devices and MMICs.
Power HEMT Device fabrication, RF and Power Characterization
Development of HEMT device fabrication technology involves a large number of unit processes that are
Integrated to realize the devices with reliable and reproducible performance. The first tryst with GaN power device development involved generation of complete technological know-how ab initio. The design of Process Evaluation Vehicles (PEVs) for process development and assessment was the first step.
Suitable Process Control Monitor (PCM) structures were incorporated for a strict monitoring of the fabrication process. Unit processes like formation of ohmic and Schottky metal contacts, device passivation, dry etching for contact-formation/device-isolation, plated air bridge interconnection for reduced parasitic, etc., were successfully developed and integrated. Surface passivation is one of the most important processes in GaN power HEMT technology. Optimum passivation mitigates the well-known phenomena of current collapse and I-V knee walkout. Reduced current collapse and knee walk-out results into higher output power density and long term device reliability in GaN HEMTs. The process of GaN HEMT surface passivation was optimized for current recovery and achieving high breakdown voltage. RF measurements on GaN HEMT involving high power densities require development of a thorough understanding of the complexities therein. Specialized measurement setup and methodologies were developed for this purpose. A dedicated load pull system was assembled in-house and is now being utilized regularly. As the power devices in general are oscillating and need special measurement techniques, a stabilization network was designed and fabricated to carry out the measurements. Devices fabricated with gate length of 0.4 μm and 0.25 μm demonstrated the cut-off frequencies of 33 GHz and 43 GHz, respectively. In order to achieve high performance for a given AlGaN/ GaN HEMT, features holding the maximum importance are high off-state breakdown voltage, current recovery, low gate and buffer leakage and low on-state resistance. Optimization of these features through simulations, process technology development and characterization was achieved. The main technology breakthrough included the control over breakdown voltage and knee walkout after device surface passivation through the incorporation of field plates over gates. The technology has been developed on 75 mm AlGaN/GaN on SiC substrates. Depletion mode HEMT devices with peak drain current density of 1 A/mm, peak DC trans-conductance of ~230 mS/mm and extrapolated power output of 5-6 W/mm for small periphery devices have been achieved.
Post Project Developments
Packaged devices with gate width of up to 2.4 mm were measured to give saturated output power of 7-8 W in S and C bands. The in-house developed bias tees have enabled the on-wafer load pull measurement of large periphery devices. The 3 mm devices in fish bone configuration could be measured to deliver a saturated output power of 15 W.
The enhancement of breakdown voltage by incorporating field plates, increased the device operating voltage suitability up to 50 V from 28 V operation. Also with field plates, due to reduction in peak electric field, the availability of active electron taps between gate and drain reduces drastically resulting in minimum current collapse and knee walkout. The in-house fabricated field plated devices have successfully delivered an output RF power density ~5 W/mm at 28 V and ~10 W/mm at 50 V operations up to 6 GHz.
GAN TECHNOLOGY FOR PRODUCTION
Complete process sequence of GaN HEMT device fabrication has been established at GAETEC. This involved establishing all unit processes on production systems and their integration. The main challenge in transferring and establishing any process on production system is the identification of critical factors causing process drift and their control. The production process is now established to deliver discrete HEMTs in S/C band. A completely processed GaN HEMT wafer fabricated at GAETEC was released in 2017.
AlGaN/GaN HEMT EPI-wafers have been developed on SiC substrates, achieving mobility >2000 cm-2 V-1s1 with 2o density of ~1013 cm-2. On-wafer uniformity and process repeatability has been established over a large numbers of runs. The achieved material characteristics are comparable to the state-of-the-art in material technology.
The current status of achieved power density is ~10 W/mm at 50 V and breakdown voltage greater than 150
V with field plate integration and is comparable with state-of-the-art device technology for S band applications.
CURRENT STATUS AND WAY FORWARD
AlGaN/GaN HEMT epi-wafers grown are being used for device fabrication. Currently further advancement in material technology is under process for growth of iron and carbon doped buffer-based heterostructures for further higher breakdown voltage operation in X band and beyond. Apart from this, growth technology is being upgraded to 4” diameter.
The device process technology for 0.7 μm GaN HEMT has been stabilized and established for production at GAETEC. Using the indigenously developed 0.7 μm gate GaN HEMT discrete device, a 1.7-2.1 GHz 10 W linear power amplifier circuit is successfully designed, fabricated, assembled and tested for the desired performance. The amplifier can be used in the chain as driver amplifier to feed higher capacity power amplifiers. The development for 0.25 μm technology for X band applications is at advanced stage along with passive components. This will enable speedy development of GaN-based MMICs with applications up to X band.
Source : www.drdo.gov.in
Deception jamming systems are designed to inject false information into victim radar to deny critical information on target azimuth, range, velocity, or a combination of these parameters. To be effective, a deception jammer receives the victim radar signal, modifies this signal, and retransmits this altered signal back to the victim radar. Because these systems retransmit, or repeat, a replica of the victim's radar signal, deception jammers are known as repeater jammers. The retransmitted signal must match all victim radar signal characteristics including frequency, pulse repetition frequency (PRF), pulse repetition interval (PRI), pulse width, and scan rate. However, the deception jammer does not have to replicate the power of the victim radar system.
A deception jammer requires significantly less power than a noise jamming system. The deception jammer gains this advantage by using a waveform that is identical to the waveform the radar's receiver is specifically designed to process.
Therefore, the deception jammer can match its operating cycle to the operating cycle of the victim radar instead of using the 100% duty cycle required of a noise jammer. To be effective, a deception jammer's power requirements are dictated by the average power of a radar rather than the peak power required for a noise jammer. In addition, since the jammer waveform looks identical to the radar's waveform, it is processed like a real return. The jamming signal is amplified by the victim radar receiver, which increases its effectiveness. The reduced power required for effective deception jamming is particularly significant when designing and building self-protection jamming systems for tactical aircraft that penetrate a dense threat environment. Deception jamming systems can be smaller, lighter, and can jam more than one threat simultaneously. These characteristics give deception jammers a great advantage over noise jamming systems.
Although deception jammers require less power, they are much more complex than noise jammers. Memory is the most critical element of any deception jammer. The memory element must store the signal characteristics of the victim radar and pass these parameters to the control circuitry for processing. This must be done almost instantaneously for every signal that will be jammed. Any delay in the memory loop diminishes the effectiveness of the deception technique. Using digital RF memory (DRFM) reduces the time delay and enhances deception jammer effectiveness. Deception jamming employed in a self-protection role is designed to counter lethal radar systems. To be effective, deception jamming systems must be programmed with detailed and exact signal parameters for each lethal threat.
The requirement for exact signal parameters increases the burden on electronic warfare support (ES) systems to provide and update threat information on operating frequency, PRF, PRI, power pulse width, scan rate, and other unique signal characteristics. Electronic intelligence (ELlNT) architecture is required to collect, update, and provide changes to deception jamming systems. In addition, intelligence and engineering information on exactly how a specific threat system acquires, tracks and engages a target is essential in identifying system weaknesses. Once a weakness has been identified, an effective deception jamming technique can be developed and programmed into a deception jammer. For example, if a particular radar system relies primarily on Doppler tracking, a Doppler deception technique will greatly reduce its effectiveness. Threat system exploitation is the best source of detailed information on threat system capabilities and vulnerabilities. Effective deception jamming requires much more intelligence support than does noise jamming.
Most self-protection jamming techniques employ some form of deception against a target tracking radar (TTR). The purpose of a TTR is to continuously update target range, azimuth, and velocity. Target parameters are fed to a fire control computer that computes a future impact point for a weapon based on these parameters and the characteristics of the weapon being employed. The fire control computer is constantly updating this predicted impact point based on changes in target parameters. Deception jamming is designed to take advantage of any weaknesses in either target tracking or impact point calculation to maximize the miss distance of the weapon or to prevent automatic tracking.
FALSE TARGET JAMMING
False target jamming is an effective jamming technique employed against acquisition, early warning, and ground control intercepts (GCI) radars. The purpose of this type of jamming is to confuse the enemy radar operator by generating many false target returns on the victim radar scope. When false target deception jamming is successfully employed, the radar operator cannot distinguish between false targets and real targets.
To generate false targets, the deception jammer must tune to the frequency, PRF, and scan rate of the victim radar. The jamming pulse must appear on the radar scope exactly like a radar return from an aircraft. Multiple false targets greater in range than the jammer are generated by delaying the transmission of a jamming pulse until after the victim radar pulse has been received. False targets closer in range are generated by anticipating the arrival of a radar pulse and transmitting a jamming pulse before the victim radar pulse hits the aircraft. If the victim radar employs a jittered PRF, only targets greater in range can be generated.
To generate different azimuth false targets, the deception jammer synchronizes its transmitted pulse with the victim radar's sidelobes. Due to their reduced power, when compared to the main beam, sidelobes are difficult to detect and analyze. The receiver in the deception jammer must be sensitive enough to detect these sidelobes and not be saturated by the power in the main radar beam. A false target deception jammer must inject a jamming pulse that looks like a target return into these sidelobes. To penetrate the radar sidelobes requires a lot of power. However, the power must be judiciously used. If a powerful jamming pulse is injected into the main beam, the false targets will be easy to detect. Most false target jammers vary the power in the jamming pulse inversely with the power in the received signal, on a pulse-by-pulse basis. This means the repeater jamming signal is at minimum power when the main beam of the victim radar is on the aircraft and at maximum power when the sidelobes are being jammed. To effectively generate false azimuth targets, the jammer must have a receiver with a wide dynamic range to detect both the main beam and the sidelobes. In addition, the jamming system must be able to generate high power that can be effectively controlled by the receiver.
To generate moving false targets, the deception jammer must synchronize with the main beam and the sidelobes in frequency, pulse width and PRF. Amplitude modulated jamming signals, with variable time delays, are transmitted into the sidelobes of the victim radar. The variable time delay provides a false target that changes range, either toward or away from the radar, depending on the time delay. The amplitude modulation provides false azimuth targets that appear to be moving.
The effectiveness of false target generation is based on the credibility of the generated false radar returns. If the victim radar can easily distinguish between false returns and target returns, the technique is a failure. The false returns must look identical to an aircraft return. The radar return on the victim radar scope should have the same intensity, depth, and width as a target return.
RANGE DECEPTION JAMMING
Although a specific TTR can track multiple targets and direct multiple weapons, the tracking circuit must select a single target return and track it while ignoring all other returns. Target selection is done by using gate bins. The range gate is used as the primary gate for target selection. A range gate is an electronic switch that is turned on for a period of microseconds based on a certain range or time delay after a pulse is transmitted
Range deception jamming exploits any inherent weakness in a TTR's automatic range gate tracking circuits. When a TTR's range gate locks on to an aircraft, the range deception jammer detects the radar signal. The range deception jammer then amplifies and retransmits a signal much stronger than the radar return. This retransmitted signal, called a cover pulse, is displayed in the range gate with the target signal.
The automatic gain control (AGC) circuit lowers the gain in the range tracking gate to control the amplitude of the cover pulse in the range gate. Reduced gain causes the real target return to be lost, and the range gate only tracks the jamming signal. This is known as range gate capture.
Once the range gate is captured by the cover pulse, a technique called range gate pull-off (RGPO) is employed. The deception jammer memorizes the radar signal and introduces a series of time delays before retransmitting. By increasing these time delays, the range gate will detect an increase in range and automatically move off to a false range. Once the range gate has moved well away from the real target, the range deception jammer shuts down, and the radar range gate is left with no target to track. The range gate breaks lock and the TTR must again go through the process of search, acquisition, and lock-on to re-engage the target.
There are several advantages of range deception jamming, especially when used as a self-protection technique. It can generate sufficient errors to deny range information and is effective against most automatic range tracking systems. This technique does not require a large amount of power, just enough to cover the radar return of the aircraft. If the time delays are not exaggerated, an operator may not detect the loss of range lock-on until after a missile has been fired. The insidious nature of range deception jamming may generate enough miss distance to save the aircraft and pilot.
There are disadvantages to using range deception jamming. First, it can be defeated by a trained radar operator. If the operator detects a problem with the automatic range tracking circuit, the system can be switched to manual range tracking mode to defeat RGPO. Also, if the threat system is still able to track the aircraft's azimuth and elevation, range information may not be required to complete target engagement. To maximize range deception jamming effectiveness, it should be employed in conjunction with azimuth and elevation jamming. Finally, this type of range deception jamming is not effective against a leading-edge range tracking system. A leading-edge tracker will not see the delayed cover pulse. As the cover pulse moves off the target, AGC circuits reset the gain to continue tracking the real target. The only way to defeat a leading edge range tracker is with a deceptive jammer that anticipates the next radar pulse and sends a jamming cover pulse before it reaches the aircraft. This jamming technique can also be defeated by randomly varying the radar PRF.
ANGLE DECEPTION JAMMING
Angle deception jamming is designed to exploit weaknesses in the angle tracking loop of the victim radar. The specific technique depends on the tracking method used to derive azimuth and elevation information. Inverse amplitude modulation jamming is the main angle deception technique used against TWS radars. For conical scan radars, scan rate modulation and inverse gain jamming are used. Swept square wave (SSW) jamming is used against LORO tracking radars.
The azimuth and elevation tracking loop for TWS radar is based on target signal amplitude modulation. The inverse amplitude modulation jammer generates a signal with modulation exactly opposite the expected return. To accomplish this, the angle deception jammer must receive the radar signals from the tracking beams. The jammer responds with a signal of the same frequency, PRF, and scan rate synchronized to the inverse of the radar antenna pattern. This induces an error in the angle tracking gate that, over a series of scans, causes the radar to lose target angle tracking.
Inverse gain jamming is also effective against conical scan radars. Since conical scan radars use the phase of the target returns to generate error signals, an inverse gain deception jammer attempts to alter the phase by inducing fake signals into the antennas. In addition, by altering the amplitude of the signal, the jammer induces large errors into the tracking loop. To accomplish this, the jammer must determine the frequency, PRF, and scan rate of the victim radar. It then transmits signals that change the phase and amplitude of the target signal, resulting in a signal 180 degrees out of phase with the actual target. This 180-degree error rapidly drives the antenna off the target and causes break-lock.
Scan rate modulation is also used against conical scan radars. This angle deception technique modulates the jamming pulse at or near the victim radar nutation frequency. As the modulation approaches the radar's nutation frequency, large error signals appear in the radar servo tracking loops, producing random gyrations in the antenna system, causing break-lock. This technique is most effective if the modulation jamming is slowly swept in frequency until it matches the nutation rate.
Both inverse scan and scan rate modulation jamming require very little power and have proven extremely effective against TWS and conical scan radars. To be effective, however, the angle deception jammer must find the precise scan rate of the victim radar. The jammer must concentrate on one signal at a time, limiting the number of threat systems that can be jammed simultaneously. In a dense threat environment, this can be a severe limitation.
The effectiveness of inverse gain and scan rate modulation jamming led radar designers to employ antennas that scan only during the receiving function of the radar system. Generally, this is accomplished by using two antennas. The transmitting antenna illuminates the target. Receiving antennas scan to produce the amplitude modulation of the reflected signal for effective angle tracking. This technique is called Lobe-On-Receive-Only (LORO). Since the transmitting antenna does not nutate, or scan, angle deception jammers cannot detect the modulation required to generate effective inverse gain modulation. Swept square wave (SSW) jamming is the angle deception technique developed to counter LORO angle tracking.
SSW jamming continuously varies the frequency of amplitude modulation on the jamming pulse over an expected range of nutation or scanning frequencies. This range is established by either electronic intelligence (ELINT) data on a particular system, or by exploitation. The dotted line in shows a threat's nutation or scan frequency. As the frequency of the modulated jamming pulse approaches the threat scan frequency, it induces errors in the angle tracking loop of the victim radar. The longer the SSW jamming stays near the scan frequency, the greater the induced errors. It is important that the sweep rate of the modulating jamming be slow enough to maximize its impact on the victim radar.
VELOCITY DECEPTION JAMMING
Pulse Doppler and continuous wave (CW) radars track targets based on velocity or Doppler-shifted frequency. The objective of velocity deception jamming is to deny velocity tracking information and generate false velocity targets. The primary techniques include velocity gate pull-off (VGPO), Doppler noise, narrow band Doppler noise, and Doppler false targets.
Velocity gate pull-off counters pulse Doppler or CW radars by stealing the velocity gate of their automatic tracking loop. The objective of VGPO is to capture the Doppler velocity tracking gate by transmitting an intense false Doppler signal. Then the frequency of the false signal is changed to move the tracking gate away from the true target Doppler. This is analogous to the RGPO technique used against the range gate tracking loop.
To accomplish an effective VGPO technique, the jammer receives the CW or pulse Doppler signal. It then retransmits a CW or pulse Doppler signal that is higher in power than the return from the aircraft, but at approximately the same Doppler frequency. It is important that the frequency of this initial jamming pulse appears within the same velocity tracking filters as the target return or the victim radar will disregard it. The frequency band of the Doppler tracking filters is an important piece of intelligence information. The velocity tracking gates are quite narrow, roughly 50 to 250 MHz. Once the jamming pulse appears in the tracking gate, the automatic gain control circuit gains out the target return, and the jamming pulse has captured the velocity gate.
Once the jamming pulse has captured the tracking gate, the deception jammer slowly changes the Doppler frequency. This frequency shift is accomplished by several methods. The most common method uses frequency modulation (FM) within the jammer’s traveling wave tube (TWT). By varying the TWT voltage, the Doppler frequency of the jamming pulse is changed linearly, and the radar tracking gates follow the jamming pulse. By using FM, the jamming pulse can be moved in either a positive or negative direction, depending on the slope of the voltage. By slowly changing the frequency of the modulation, the jamming pulse pulls the tracking gates off the target. When the maximum offset has been achieved, nominally 5 to 50 kHz, the FM is “snapped back” to a minimum value, and the process is repeated to preclude target reacquisition.
The rate of change of frequency offset in a VGPO pulse is an extremely critical parameter. Many CW and pulse Doppler radars employ acceleration stops as part of the tracking gates. By differentiating the velocity outputs of the velocity tracking gates with respect to time, the velocity tracker computes target acceleration. Acceleration stops detect and reject unusually large changes in target acceleration. If the VGPO technique changes the frequency of the jamming pulse too rapidly, the tracking loop, with acceleration stops, will reject the jamming pulse and stay on the target. This means that an effective VGPO technique may take from one to ten seconds.
Doppler noise differs from most noise techniques in that it is a repeater technique. The jamming system must receive the pulse Doppler radar signal in order to generate an appropriate jamming pulse. Also, noise jamming output is done on a pulse-by-pulse basis and only lasts as long as the pulse duration, or pulse width, of the victim radar signal. The Doppler noise jammer receives each pulse and applies a random frequency shift, either positive or negative, to each pulse.
When Doppler noise jamming pulses are processed by the signal processor, and the Doppler frequencies are sent to the velocity tracking gate, there are so many different velocities that the tracking gate cannot distinguish the target from the jamming. The random distribution of target velocities effectively masks the true target Doppler velocity. If the velocity tracking loop is not saturated, multiple false targets traveling at different speeds will be displayed.
When a technique called Doppler noise blinking is employed, it interferes with the angle and velocity tracking within most semi-active radar missiles. Doppler noise blinking is accomplished by rapidly transmitting bursts of Doppler noise jamming.
Doppler noise jamming is effective against most pulse Doppler radars and the semi-active missiles employed with these radars. One disadvantage, however, is that it is only effective against the velocity tracking loop. If range tracking is still available to the radar, Doppler noise may highlight the jamming aircraft. Another disadvantage is that Doppler noise requires a sophisticated jammer able to receive the victim radar pulse, generate random positive and negative frequency modulations on this pulse, and retransmit the jamming pulses at the PRF and pulse width of the victim radar. This requires an extremely fast signal processing capability and detailed intelligence information on the victim radar.
Narrowband Doppler noise is also a repeater technique. The jamming system receives the pulse Doppler radar signal and generates a noise jamming signal on a pulse-by-pulse basis . Narrowband Doppler noise requires detailed information on the frequency coverage of an individual velocity tracking filter, or velocity bin, employed by the victim radar. Once this frequency range is known, the jammer receives each pulse from the victim radar and transmits jamming pulses with a higher and lower frequency shift based on the real target Doppler. These frequency shifts are always within the frequency range of the velocity bin.
When these pulses are processed by the signal processor and the Doppler signals are sent to the velocity tracking gates, the particular bin that contains the target Doppler also contains several other targets generated by the jammer. The victim radar signal processor attempts to distinguish the target Doppler from the jamming pulses. It raises the gain in the velocity tracking bins, thinking that the signal with the highest amplitude is the target. But, as the signal gain is increased, the target is “gained out” with the jamming signals and no target is displayed. This is called velocity bin masking and can completely deny target information to a pulse Doppler radar.
The advantage of narrowband Doppler noise is that it completely masks an aircraft's velocity from a pulse Doppler radar. The disadvantages include the following: When the victim radar can range-track an aircraft, narrowband Doppler noise highlights the aircraft's presence. To be effective, narrowband Doppler noise requires knowledge of the frequency range of the victim radar's velocity tracking bins, or filters. This detailed information may be available only through threat system exploitation. Finally, sophisticated signal processing and jamming systems are required to receive and transmit in the very narrow frequency band of the velocity bin.
Doppler false target jamming is normally used with narrowband Doppler noise or other deception techniques. Its purpose is to initially confuse the radar signal processor with multiple targets and then force the radar signal processor to raise its gain levels in the velocity tracking loop. The Doppler false target jammer receives each pulse of the victim radar and applies a random frequency shift to a selected number of these pulses.
The selected pulses are processed by the signal processor, and multiple Doppler frequencies are sent to the velocity tracking gate. In an attempt to distinguish the target from the jamming pulses, the signal processor increases the gain in each tracking filter, assuming the target Doppler has a higher amplitude than the jamming pulses. This increase in gain sets up the velocity tracking loop for a narrowband Doppler noise technique that will cause the real target to be lost among the generated false targets.
The advantage of Doppler false target jamming is that it can initially confuse the radar signal processor and the radar operator as to the velocity of the real target. It also sets up the radar for narrowband Doppler noise technique and increases its effectiveness. The disadvantage is that the signal processor or the radar operator will eventually be able to distinguish the real target from the false targets based on its velocity. This jamming technique is much more effective when used in conjunction with other Doppler jamming techniques.
MONOPULSE DECEPTION JAMMING
The ability of monopulse tracking radars to obtain azimuth, range, and elevation information on a pulse-by-pulse basis make them extremely difficult to jam. Amplitude modulation jamming used against conical scan or TWS radars, such as inverse scan and swept square wave, highlights a target, making monopulse tracking easier. Frequency modulation techniques, such as RGPO and VGPO, are equally ineffective. They serve as a beacon that aids the monopulse radar's target tracking ability. The monopulse radar may be able to track the jammer with more accuracy than tracking actual radar returns because target glint effects are absent from the jamming pulse. Monopulse angle jamming techniques can be divided into two main categories, system-specific and universal. Examples of system-specific jamming techniques include skirt frequency jamming, image jamming, and cross-polarization jamming. These techniques attempt to exploit weaknesses in the design and operation of specific monopulse radars. Cross-eye jamming, a universal technique, attempts to exploit all monopulse radar systems.
Skirt frequency jamming, or filter skirt jamming, is designed to counter the monopulse receiver. Skirt frequency jamming is based on the fact that the intermediate frequency (IF) filter of the monopulse receiver must be correctly tuned to the transmitting frequency of the monopulse radar. It these two components are not exactly tuned, the target signal may be presented on the edge, or skirt, of the receiver IF filter. This offers an opportunity to inject a jamming signal into this skirt
Filter skirt jamming attempts to take advantage of this frequency imbalance by transmitting a jamming pulse tuned slightly off the radar transmitted frequency and in the middle of the receiver IF filter. This jamming pulse will generate a false error signal and drive the antenna away from the true target return.
A well designed and maintained monopulse system does not have a frequency imbalance. The transmitter and IF filter frequencies will be identical. Jamming signals that are even slightly out of this narrow frequency range will not affect the monopulse tracking capability of the radar.
Effective filter skirt jamming requires extensive knowledge of the internal operation of the IF filter. This information can normally be obtained only by system exploitation. Variances from radar to radar and frequency imbalance exists from one radar IF filter to another. This creates a high degree of uncertainty in the effectiveness of this technique.
Image jamming exploits another potential weakness in the monopulse receiver. Some monopulse receivers have a wide-open front end with no preselection before the mixer. If the jammer transmits a pulse at the intermediate, or image, frequency, but out of phase with this frequency, the phase of the target tracking signal will be reversed and the antenna will be driven away from the target . Effective image jamming requires detailed information on the operation of the monopulse receiver. Of particular importance are the image, or intermediate, frequency and whether the local oscillation frequency is above or below the transmitted frequency. This may require exploitation of the monopulse threat system. In addition, a well-designed monopulse system has preselection in the front end and will reject signals that are out of phase with the transmitted frequencies. This capability renders image jamming ineffective.
Effective filter skirt jamming requires extensive knowledge of the internal operation of the IF filter. This information can normally be obtained only by system exploitation. Variances from radar to radar and frequency imbalance exists from one radar IF filter to another. This creates a high degree of uncertainty in the effectiveness of this technique.
Image jamming exploits another potential weakness in the monopulse receiver. Some monopulse receivers have a wide-open front end with no preselection before the mixer. If the jammer transmits a pulse at the intermediate, or image, frequency, but out of phase with this frequency, the phase of the target tracking signal will be reversed and the antenna will be driven away from the target. Effective image jamming requires detailed information on the operation of the monopulse receiver. Of particular importance is the image, or intermediate, frequency and whether the local oscillation frequency is above or below the transmitted frequency. This may require exploitation of the monopulse threat system. In addition, a well-designed monopulse system has preselection in the front end and will reject signals that are out of phase with the transmitted frequencies. This capability renders image jamming ineffective.
Cross-polarization jamming exploits the difference in the monopulse antenna pattern for a jamming pulse that is polarized orthogonal to the design polarization. The antenna pattern for a two-channel monopulse radar using sigma and delta beams shows the tracking point to be between the two beams .This is true if the radar is using its design polarization. However, the radar antenna also has a receiving pattern for a signal that is cross-polarized with the design frequency. For a cross-polarized signal, the tracking point is shifted one beamwidth to the right. This shift in the tracking point results in a target tracking signal that is 180° out of phase with the real signal. To be effective, a jamming signal polarized orthogonally to the design frequency of the radar would have to be 25 to 30 decibels, or about 1000 times, stronger than the radar signal.
A cross-polarized jammer must receive and measure the polarization of the victim monopulse radar. The jammer then transmits a very high power jamming signal at the same frequency, but orthogonally polarized, to the victim radar. As a rule, the jamming signal must be 25 to 30 dBs stronger than the target return to exploit the tracking errors in the cross-polarized antenna pattern. Additionally, it must be as purely orthogonal to the design polarization as possible. Any jamming signal component that is not purely orthogonal will highlight the target and require more jamming power to cover the target return.
A cross-polarized jammer must be able to generate a powerful jamming pulse that is polarized orthogonal to the victim radar. A cross-polarized jammer that generates the power and purity of polarization required to defeat monopulse angle tracking poses extreme technological challenges.
Cross-eye jamming is a complex technique that attempts to distort the wavefront of the beams in a monopulse radar and induce angle tracking errors. It exploits two basic assumptions of monopulse tracking logic in comparing target returns on a pulse-by-pulse basis. The first assumption is that a target return will always be a normal radar pulse echo. The second assumption is that any shift in amplitude or phase in a target return is due to the tracking antenna not pointing directly at a target. This condition generates an error signal and the antenna tries to null, but the amplitude or phase shifts.
Cross-eye jamming attacks the two assumptions through a process of receiving and transmitting jamming pulses from different antennas separated as far apart as possible.The phase front of a monopulse signal is received by the number 1 receive antenna, amplified by the repeater, and transmitted by the number 2 transmit antenna. The same phase front then hits receive antenna number 2, is shifted 180°, amplified by the repeater, and transmitted by the number 1 transmit antenna. These two out-of-phase signals must be matched in amplitude and must exceed the amplitude of the target return.
When these jamming signals arrive at the victim radar, the tracking loop attempts to null out the amplitude and phase differences. With two widely spaced jamming sources at different phases, the antenna never achieves a null position or tracking solution. The distance between antenna pairs is an important parameter that determines the effectiveness of cross-eye jamming. The wider the spacing between antenna pairs, the more distortion in the victim's wave front near the true radar return. Most fighter aircraft do not provide sufficient spacing between the antennas to maximize effectiveness. Effectiveness is also lost when the aircraft is abeam or going away from the radar. To further complicate matters, when the radar is directly in front of the aircraft, the jamming pulses must have a power at least 20 dBs above the target return. Cross-eye jamming can also be defeated with a leading-edge tracker that rejects jamming signals arriving at the antenna behind the target return.
Countering monopulse angle tracking is the greatest challenge for selfprotection jamming systems. Skirt jamming and image jamming have had limited success. Cross-polarization and cross-eye jamming techniques require complex and sophisticated circuitry and much power.
Terrain bounce is a jamming technique used primarily at low altitude. It is used to counter semi-active, air-to-air missiles and monopulse tracking radars. The technique involves a repeater jammer that receives the radar or missile guidance signal. The jammer amplifies and directs this signal to illuminate the terrain directly in front of the aircraft. The missile or radar tracks the reflected energy from the spot on the ground instead of the aircraft.
To be effective, the terrain bounce jamming antennas should have a narrow elevation beamwidth and a broad azimuth beamwidth. This transmission pattern maximizes the energy directed toward the ground and minimizes the energy transmitted toward the missile or radar. To overcome signal losses associated with uncertain terrain propagation, the jamming system should also generate high jamming power. This ensures the energy reflected from the terrain is higher than the energy in the aircraft return. The terrain bounce jamming antennas should have very low sidelobes to preclude activation of any home-on-jam (HOJ) missile capability. For an air-to-air missile, the terrain bounce technique should be activated at long range. This will initially put the aircraft and the jamming spot in the same resolution cell. As the range decreases, the missile will be decoyed by the higher power in the jamming spot.
Some problems associated with terrain bounce jamming include the uncertainty of the signal scattering parameters of the various terrain features and the possible changes in signal polarization caused by terrain propagation. In addition, terrain bounce jamming can place maneuvering restrictions and maximum altitude limitations on the aircraft.
There is several deception jamming techniques that can be employed to counter threat radar systems. The effectiveness of these techniques can be enhanced when they are employed in combination. For example, the effectiveness of an RGPO technique is enhanced when an angle deception technique is also employed. Determining the most effective deception technique, or combination of techniques, can present a challenge to intelligence and engineering analysts. However, when employed with maneuvers and chaff, deception techniques can mean the difference between success and failure on the modern battlefield.
A radar noise jamming system is designed to generate a disturbance in a radar receiver to delay or deny target detection. Since thermal noise is always present in the radar receiver, noise jamming attempts to mask the presence of targets by substantially adding to this noise level. Radar noise jamming can be employed by support jamming assets or as a self-protection jamming technique. Radar noise jamming usually employs high-power jamming signals tuned to the frequency of the victim radar.
RADAR NOISE JAMMING EFFECTIVENESS
The effectiveness of radar noise jamming depends on numerous factors. These factors include the jamming-to-signaI (J/S) ratio, power density, the quality of the noise signal, and the polarization of the transmitted jamming signal.
One of the most important factors that impacts the effectiveness of radar noise jamming is the J/S ratio .The power output of the noise jammer must be greater than the power in the target return, as measured at the output of the radar receiver. To achieve this level of jamming power, radar noise jammers usually generate high-power jamming signals. These high-power jamming signals can be introduced into the victim radar's main beam to deny range information and into the victim radar's sidelobes to deny azimuth information.
Another factor which impacts the effectiveness of radar noise jamming is the power density. The power density of the noise jamming signal has a direct relation to the J/S ratio.
If the noise jamming signal is centered on the frequency and bandwidth of the victim radar, the jamming signal has a high power density. The ability of a noise jammer to concentrate the jamming signal depends on the ability of the jammer to identify the exact frequency and bandwidth of the victim radar.
If the generated noise jamming signal has to cover a wide bandwidth or frequency range, the power density at any one frequency is reduced. Radar systems that are frequency agile or that employ a wide bandwidth can reduce, or negate, the effectiveness of noise jamming by reducing the power density of the jamming signal.
The quality of the noise jamming also determines its effectiveness. To effectively jam a radar receiver with noise, the jamming signal must emulate the thermal noise generated by the receiver. This ensures that the radar operator or automatic detection circuit cannot distinguish between the noise jamming and normal thermal noise. Thermal noise is referred to as white noise and has a uniform spectrum. All of the frequencies in the bandwidth of the receiver have the same spectrum and amplitude that varies based on Gaussian distribution. A Gaussian distribution is simply a bell-shaped distribution of amplitudes. In order to be effective, the jamming signal should exactly match the characteristics of the thermal noise signal of the victim radar receiver.
Polarization of the noise jamming signal is another significant factor that impacts its effectiveness. As discussed in Chapter 2, if the polarization of the jamming signal does not match the antenna polarization of the victim radar, there is a significant power loss in the jamming signal. Noise jamming systems designed to counter multiple threat radars, with various polarizations, generally use a transmitting antenna with a 45° slant or use circular polarization. Most threat systems are horizontally or vertically polarized. This results in a 50% reduction in effective radiated power (ERP) for most threat systems. A more serious power loss, nearly 100%, in ERP occurs when the jamming antenna is orthogonally polarized with the victim antenna. The polarization of the noise jamming signal impacts the J/S ratio and the power density.
in pic noise modulated jamming
RADAR NOISE JAMMING GENERATION
Noise jamming is produced by modulating an RF carrier wave with random amplitude or frequency changes, called noise, and retransmitting that wave at the victim radar's frequency. Since noise from numerous sources is always present and displayed on a radar scope, noise jamming adds to the problem of target detection. Reflected radar pulses from target aircraft are extremely weak. To detect these pulses, a radar receiver must be very sensitive and be able to amplify the weak target returns. Noise jamming takes advantage of this radar characteristic to delay or deny target detection.
The simplest method of generating a high-power Gaussian noise jamming signal is to employ a highly amplified diode to generate a noise signal at the frequency of the victim radar. This signal is filtered and directly amplified to the maximum power that can be generated by the transmitter. This method is called direct noise amplification (DINA). The DINA method of noise generation has a serious limitation. The maximum power available from linear wideband power amplification is extremely limited. Employing any other form of power amplification would alter the Gaussian distribution of the jamming signal. This method of generating radar noise jamming was used extensively during WW II.
Modern noise jamming systems generate noise jamming signals by frequency modulating a carrier wave at the frequency of the victim radar. FM noise jammers employ a receiving antenna to intercept the victim's radar signal. The antenna passes the victim radar signal to the receiver for identification. The receiver also tunes the jamming signal generator to the correct frequency. The receiver uses an automatic frequency control (AFC) circuit to tune the voltage controlled oscillator (VCO) to the frequency of the victim radar. A noise signal is generated by the jamming signal generator and added to the tuning voltage of the VCO to get an FM jamming signal. This signal is sent to a traveling wave tube (TWT) power transmitter. The TWT is normally operated in a saturated mode which produces a high-power jamming signal that covers a wider bandwidth than the victim radar. This reduces the power density of the signal, but the high power levels available from the TWT amplification of an FM signal compensate for this loss. The signal is sent to the transmitting antenna and directed toward the victim radar. An increasing of the noise will decrease the probability of detection and an increasing of the false alarm rate too.
An important feature of a modern radar noise jamming system is, a look-through capability. A look-through mode allows the receiver to periodically sample the signal environment. The objective of the lookthrough mode is to allow the jammer to update victim radar parameters and change the jamming signal to respond to changes in the signal environment. This greatly enhances the effectiveness of noise jamming systems. One method used to provide a look-through capability is to isolate the transmit and receive antennas to allow continuous operation of the receiver to update signal parameters. Another method is to switch off the jammer for a brief period to allow the receiver to sample the signal environment. Since this latter look-through method eliminates the jamming signal, the amount of time the jammer is switched off must be kept to a minimum.
An important aspect of jamming power is power density. Noise jamming depends on power density for its effectiveness. Power density is a function of the frequency range, or bandwidth, of the jamming signal. If a jammer covers a narrow frequency range, it can concentrate energy in a narrow band. If a jammer covers a wide frequency range, the energy is spread over that entire range. Since the jammer has fixed radiated power, this lowers the effective jamming power at a given frequency. Barrage jamming is a jamming technique where high power is sacrificed for the continuous coverage of several radar frequencies. The jamming signal is spread over a wide frequency range, which lowers the ERP at any one frequency. This type of jamming is useful against frequency-agile radars, against a radar system that uses multiple beams, or against multiple radar systems operating in a specific frequency range. By spreading the jamming over a wide frequency range, there is some level of jamming no matter what frequency the radar uses. Barrage jamming was used extensively during World War II. Advantages of barrage jamming are its simplicity and ability to cover a wide portion of the electromagnetic spectrum. The primary disadvantage is the low power density, especially when a high J/S ratio is needed against modern radars.
One way to take advantage of the noise jammer's simplicity, but raise the jamming signal power, is to use a spot jammer. The earliest spot jammers were very narrow band jammers covering a bandwidth of 10 megahertz or less .This narrow band spot jammer was tuned to the anticipated frequency of the target radar. When it is necessary to jam a number of radars at different frequencies, more than one jammer is used. One problem that developed was of carrying the required number of spot jammers to counter a modern lADS. Also, radars that change their operating frequency, or are frequency-agile, defeat the spot jammer. Today, intercept panoramic receivers work with spot jammers to determine the frequency of the victim radar. A look-through capability is included in the system so that the target radar signal can be monitored to assess jamming effectiveness. The jamming signal can be adjusted for any changes in the operating frequency of the radar.
The primary advantage of spot jamming is its power density. Radar or communications receivers can be countered at longer ranges than when using a barrage jammer of equal output power.
A disadvantage of the spot jammer is its coverage of a narrow band of the frequency spectrum. An operator or computer in the receiver must constantly monitor and tune the jamming signal to the target radar's frequency. The complexity of this process increases when jamming frequency-agile radars that can change frequencies with every pulse.
When high power density is required over a large bandwidth, one solution is to take spot jamming and sweep it across a wide frequency range . This preserves the high power density but allows the jamming to cover a large bandwidth. The jamming spot is swept across a broad frequency range at varying speeds. With this technique, a number of radar systems can be covered. Because of their high jamming power, swept-spot jammers are able to cover a number of radars operating in a broad frequency range. However, jamming is not continuous. Fast swept-spot jamming can approximate continuous jamming by causing a phenomenon known as “ringing.” Fast sweeping spot noise is like a burst of energy which sets up vibrations within the receiver section. When these vibrations last until the next burst of energy is received, this is known as ringing.
Three factors determine swept-spot jamming effectiveness. The first is the power in the spot. The next is the bandwidth, or frequency range, the spot covers. The last is the sweep rate.
COVER PULSE JAMMING
Cover pulse jamming is a modification of swept-spot jamming. This is a “smart noise” technique that is responsive for a short period of time . A repeater jammer acts as a transponder. It receives several radar pulses and determines the PRF (pulse repetition frequency) of the victim radar. It then uses this data to predict when the next radar pulse should arrive. Using an oscillator that is gated for a period of time based on predicted pulse arrival time, a noise-modulated signal is amplified and transmitted. This process works against a radar with a steady PRF, and allows a low-powered repeater to respond to a number of threats by time-sharing.
Cover pulse jamming is used to initiate a range gate pull-off (RGPO) deception jamming technique. The deception jammer transmits a noise jamming signal, or cover pulse, which is much stronger than the target return. The cover pulse raises the automatic gain inside the range gate, and the range tracking loop initiates tracking on the cover pulse. The deception jammer then increases the time delay in the jamming pulse and moves the range tracking gate away from the real target.
A form of cover pulse jamming is also used to initiate a velocity gate pulloff (VGPO) technique against continuous wave and pulse Doppler radars. The cover pulse, in this case, is a strong jamming signal with the same frequency shift as the aircraft return. This cover pulse steals the velocity tracking gate and sets up the velocity tracking loop to steal the velocity tracking gate based on false target Doppler shifts.
MODULATED NOISE JAMMING
Modulated jammers are special hybrid jammers which employ noise jamming that is either amplitude or frequency modulated. The purpose of this modulated noise is to defeat target tracking radars (TTRs) rather than deny range information. Modulated noise jamming has proven effective against conical scan and trackwhile- scan (TWS) TTRs.
Modulated jamming alters the noise jamming signal at a frequency that is related to the scan rate of the target radar. If modulated jamming is used against conical scan radar, a sine wave signal is used. The frequency of the sine wave is slightly higher than the scan rate of the victim radar. The amplitude difference results in a constantly varying phase between the radar and the jamming signal. This phase differential produces false targets with a strong signal amplitude everywhere the signals reinforce each other. This causes the conical scan radar to track the false returns and lose the real target return. For this technique to work, the scan rate of the intended victim radar must be known.
Against TWS radar, a rectangular waveform is used to modulate the noise signal. The PRF of the modulation is set at some harmonic of the TWS rate. This synchronization results in a number of jamming strobes on the radar scope. Each jamming strobe is at a different azimuth or elevation depending on which radar beam is being jammed. The number of jamming strobes depends directly on the harmonic used to modulate the signal. In Figure, a modulating signal frequency that is four times the scan rate of the radar will produce four jamming strobes on the scope. If the jamming is slightly out of tune with the scan rate, the jamming strobes will appear to roll across the radar scope.
Radar noise jamming is employed to deny target acquisition and target tracking data to victim radar. This is accomplished by injecting amplitude or frequency modulated noise jamming signals into the victim radar's receiver. The effectiveness of the above mentioned noise jamming techniques depends on the power density of the jamming signal compared to the power in the radar return, or the J/S ratio. Radar noise jammers are generally simple, high-power systems which can be effectively employed in a support or self-protection role. Radar noise jamming can be employed in conjunction with deception jamming techniques to maximize the impact of jamming on victim radars.
With passage of time the adversary has grown stronger. If they want to, they won't directly launch a mass attack of ballistic missiles, but would rather use tactics, to saturate radar stations, employ jamming. Thus a need arises for unhindered surveillance of the airspace so that threat monitoring mechanisms can alert the respondents to quickly neutralise threats. The mission needs of Indian Air Force (IAF) is to have a gap free coverage for aerial threats from medium level height, 2 km, and above for a range up to 300 km. Until recently, these needs are met by PSM-33, P-40 and TRS-2215 kind of radars. However the service livesof these radars are over and any change in doctrine/tactics cannot overcome the void without any material solution. To overcome this void the Indian AirForce was in dire need of a next generational platform that can accurately detect the conditions of an alien object as well deal with any effort to neutralise the system. This led IAF to set up operational requirements keeping in mind newly available techs. The operational requirement was for the development of 4D rotating, phased array Medium Power Radar (MPR).
The story of development of this advanced 4 Dimension radar is very interesting ,so is the technology involved. It is set to not just satisfy the security needs of IAF but also provide a and resistance to enemy tactics of creating any hindrance. Throughout the article we have provided carefully structured explanation of various terminologies involved in radar making as well as highly advanced technologies involved in this radar. Also provided a pinch of spicy history.
Medium Power Radar Arudhra is a 4D rotating phased array radar. It can automatically detect and track targets ranging from fighter aircrafts to ballistic missiles to slow moving targets. It can either be stable and stare or be rotated for 360° coverage. In rotation mode, the antenna rotates at 7.5 / 15 rpm with surveillance coverage of 360° in azimuth and 30° in elevation. In staring mode of operation the antenna stares in specified azimuth with surveillance coverage of ±60° in azimuth and 30° in elevation. Design, development and production of MPRs were categorized as ‘Make’ category. Electronics and Radar Development Establishment (LRDE), a Bengaluru-based DRDO establishment, took up the task and developed a fully engineered MPR for the IAF. The system has an instrumented range of 400 Km and is able to detect 2sqm RCS targets as far as 300 Km in range with the altitude coverage from 100 meters to 30 Kms.
NOTE :- ‘Buy and Make’ means buying a portion of demand, obtaining ToT and production in India for remaining demand. ‘Make’ means developed by DRDO laboratories through indigenous efforts and manufactured by an Indian production agency.
Medium Power Radar (MPR) is capable of automatic detection and tracking air intrusions at an altitude of about 100 meters up to a range of 30 km. IAF projected (November 2002) a requirement of 23 MPRs with active phased array radar technology for replacement [between X (2002-07) and XII (2012-17) Five Year Plan] of existing radars (PSM-33 radars, P-40 and TRS-2215 radars), which had completed their service life of 20 years.In active phased array each antenna has transmit / receive (T/R) modules to boost up output power of the transmitted signals required for maximum detection range.
Based on Air HQ ORs (November 2004) and due to non-availability of technology, MoD approved (April 2006) import of 15 MPRs by IAF and indigenous development of eight MPRs by LRDE with a delivery schedule of 60 months (April 2011). LRDE submitted (November 2006) a proposal to Air HQ for development of MPR using imported antenna through direct import of MAP antenna from M/s Thales, France at a cost of `97.84crore to meet IAF time frame of 36 months. However, Air HQ insisted (June 2007) LRDE to develop a fully indigenous MPR including its antenna using latest technology.
Accordingly, LRDE submitted (September 2007) revised proposal to develop active phased array technology based MPR with Digital Beam Forming (DBF) feature, Digital Beam Forming is employed to synthesize multiple signals received in the form of a beam, the Ministry sanctioned (November 2008) the project MPR ‘Arudhra’ under MM at a cost of `134.14 crore with a time frame of 54 months (May 2013) which was extended to October 2014.
The Arudhra is a 4D rotating antenna active phased array radar. It can also be stable and stare only in one direction. It uses cross pattern of five beams in azimuth and elevation is used for dedicated tracking of detected targets with good accuracy. What are these patterns? We know that AESA radars are made up of not one single antenna, but an array of multiple antennas. A radar needs to radiate waves in a single direction so that the waves strike target and get back making the antenna realise target location. But in reality it is impractical to make an antenna which is fully coherent and radiates all the waves in one direction only. An antenna even that of a radar radiates waves in all directions, but these antennas are designed in such a manner that maximum amount of waves are radiated in the desired direction. The radiation pattern of an antenna is dependent on it's shape. The pattern would be largely symmetrical to the shape of antenna. In an array of antennas the radiation coming from sides or undesired directions interferes at some angles and being out phase with each other they cancel each other out. If this is plot on a graph, the plot will show maxima at the desired direction. This Maxima is called a lobe and for an array of antennas their will be multiple lobes. Practically their will be lobes in all directions but the largest love would be in the desired direction, a direction where we intend to radiate waves. The larger the antenna is compared to a wavelength, the more lobes there will be. In a directive antenna in which the objective is to direct the radio waves in one particular direction, the lobe in that direction is larger than the others; this is called the "main lobe".
Arudhra radar has a cross pattern of 5 beams in azimuth and elevation, means that 5 beams independently scan the surrounding airspace sideways and up and down ways to locate the target, one targets are located they are tracked while still more targets are searched. The coverage is attained using wide transmit beam and multiple receive beams in both azimuth and elevation.
The system is able to survive intense ECM environment and possible electromagnetic interference. Arudhra is fully programmable from the local Operator Work Station and from remote Operator Work Station Unit. Arudhra being a 4D radar can determine range (straight distance from radar), azimuth (angular position from a reference direction), altitude (distance from ground) as well as velocity vector (representation of direction of motion) of a target.
The Radar is based on solid state active aperture phased array with Digital Beam Forming and has electronic scanning capability in both azimuth and elevation. Digital Beamforming a certain number signals first pass through an analogue to digital converter to create equal number of data streams. Then these data streams are added up digitally, with appropriate scale-factors or phase-shifts, to get the composite signals.Digital beamforming has the advantage that the digital data streams (100 in this example) can be manipulated and combined in many possible ways in parallel, to get many different output signals in parallel. The signals from every direction can be measured simultaneously, and the signals can be integrated for a longer time when studying far-off objects and simultaneously integrated for a shorter time to study fast-moving close objects, and so on.
Beamforming is achieved by combining elements in an antenna array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity.
The Arudhra is also capable of things like multi target tracking and target classification. While reconnaissance missions spy on enemy's assets they carefully record the 'reflector components’. The information about these reflector components is stored inside threat libraries of Arudhra as some picture of target already available. Then while normal operations the radar computer tries to match the reflector components of the target being tracked with the known reflector components (their are various techniques to do so) and calculate the probability of correct classification PCC if the PCC is high then the previously known designation of target is displayed on screen.
Rotating Active Phased Array
Rotating APARs are a new thing and an attractive alternative to having four arrays fixed at four directions. Many people who call Arudhra as a developed version of EL/M 2084 do not realise that the array of both hugely differ.
Time synchronization of multiple receivers.
Multiple receivers may not be receiving their own particular waves at a same time than each other. Their are variations in the amount of time needed for doing the entire operation of send and receive, synchronization problem consists of four parts: send time, access time, propagation time, and receive time. So when different receivers are observing the same thing but at different a different time which would be relativly true to their own self but may not match with other fellow receivers. To accurately determine location, proximity,speed of a target all the data received by different receivers must be synchronised with respect to time standard to all. The concept of time and time synchronization is needed in all such wireless devices.
2D Digital Beam-forming.
We have seen what is beam forming in above text, in digital beamforming amplitude and phase variation is applied before digital to analogue conversion so that a desired wave can be formed through that particular T/R module. And after receiving the signals they are converted down to digital form and then summation is done. This is amazing and unlike analogue beamforming where received analogue signals are summed up and then converted from analogue to digital. This is why AESA radars can emit waves of multiple frequencies at a smart time.
DBF based active array calibration.
For digital beam forming the calibration of phase is necessary so that the entire beam could be coherent whenever needed. For this their are various procedures and protocols to calibrate and fine tune the active array, it is very difficult process and has been done in Arudhra at a big level.
The processing of beams radiated and received by antenna array focuses on presentation of data on a 2D screen of that of a 3D airspace, classification and categorisation of threats etc.
Critical real-time software and firmware.
The real time computing guarantees the response within specified time constrained all the functions from start of scan to display of target must happen in real time, means their shouldn't be any delays for target detection Real-time responses are often understood to be in the order of milliseconds, and sometimes microseconds. If the response even taken more than one second it cannot be called real time. Development of such an advanced technology is a huge challenge overcome during AESA radar development.
Independently rotating IFF radar.
Usually the identification friend or foe IFF radar is integrated with main array itself. Friendly aircrafts are equipped radar transponder, that replies to each interrogation signal (sent by IFF radar) by transmitting a response containing encoded data. The encoded data is secretive and coded on friendlies so that radars like Arudhra interrogates the targets it is tracking and then classifies them into friend or foe.
Mechanical Packaging (Engineering, Thermal, etc.,)
Packaging focuses on mobility and quick deployment of Arudhra system. The system could be able to quickly pack and unpack so that it could be deployed in short notice. Thermal packaging is designed for temperature sensitive products that require a defined temperature to be maintained during transportation to the end user. Special thermally insulated packages need to be developed , tested, validated and produced for this purpose. All the necessary packaging systems were developed in-house by DRDO.
INDUCTION INTO SERVICE.
Arudhra is the first indigenous rotating Active Phase Array Multifunction 4D radar capable of employing state-of-
the-art DBF technology with multi beam processing for the first time in India. Radar has undergone extensive user evaluation at various locations and has been accepted by IAF for induction and is ready for production.
MPR technology can be to be used for any ship borne radar applications. The technology will be used for mountain radar and in future family of radars of LRDE for various application.
Presently MPR technology is used for similar class of radars for Indian Army. Field trails of the radar in integrated mode have carried out successfully in various locations. Usually scientists are criticised for delaying stuff and the critics have no idea about what job they have to do, when they start it they can only assume the completion of time,but while doing an entirely new thing a person never knows for sure at what time it would get completed. Fullaftetburner has always focussed on presenting selected technical data that would be a treatise to the readers interested in defence, but endless bickering won't be tolerated.
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Info Sources :-
There are some fundamental principles that apply to all types of jamming and to all jamming employment options. These principles are based on the characteristics of the jamming system and the characteristics of the victim radar. They include frequency matching, continuous interference, signal-to-noise ratio, jamming-to-signal ratio, and burnthrough range.
Based on the data provided by ES systems and intelligence evaluations, radar jamming systems must transmit signals at the frequency of the victim radar This applies to both noise and deception jamming. If a jamming signal does not match the transmitter frequency, the jamming signal is not received and displayed on the scope. When a jamming signal matches the transmitter frequency, the jamming signal is received and masks the target display .
For maximum effectiveness, a jamming transmitter should produce continuous interference. In much the same way intermittent static on a radio receiver does not completely block out a signal, intermittent jamming on a radar scope may not completely mask the target. An experienced radar operator or advanced automatic tracker can “read through” intermittent jamming and derive sufficient target information to negate jamming effectiveness. While true for noise jamming techniques, continuous interference also applies to deception techniques, especially when target reacquisition is considered.
Signal To Noise Ratio
The signal-to-noise (S/N) ratio is a measure of the ability of the victim radar to detect targets. It is also an indication of the vulnerability of the radar to certain jamming techniques, especially noise jamming.
The signal power density of the target return is so weak that it requires very strong amplification before processing and display. Besides the signal power from the target, some level of thermal noise is also generated and amplified along with the target signal.
The radar receiver amplifies both target signal and thermal noise. The output of the radar receiver will contain the target signal and the noise amplified across the bandwidth of the receiver. Separating the desired target signal from the undesired noise signal is one of the major problems confronting radar designers.
Target RCS fluctuates based on the changing angle of the antenna beam and corresponding changes in the reflected signal. Effective antenna aperture is also a statistical phenomenon based on the fluctuations in target RCS. The thermal noise generated by a receiver is also a fluctuating factor and must be treated statistically. This means that the S/N ratio is a statistical factor associated with a probability of target detection and a probability of a false alarm. A false alarm occurs when the radar operator or automatic tracking circuit designates a fluctuation in noise level as a target. The higher the S/N ratio, the higher the probability of target detection with a corresponding reduction in the probability of a false alarm.
Any action that increases the power in the target signal (for example, increasing transmitted power, increasing antenna gain/aperture area, or decreasing target range) will improve the S/N ratio and improve the probability of target detection. It would also appear that decreasing the bandwidth of the radar receiver will increase the S/N ratio and enhance the probability of target detection. However, if the effective bandwidth of the receiver is reduced, this may eliminate a significant portion of the radar signal spectrum and decrease the probability of target detection.
The S/N ratio is also an indication of the range at which a target will be detected. The weak target signal at an extended range is just above the receiver noise level.
The target at closer range is easily detected above the noise level. A radar operator or automatic target detector could mistake the very weak target return as a fluctuation in the receiver noise level. This could result in a missed detection. The lack of discrimination between noise and target returns because of a poor S/N ratio can also result in designating fluctuations in the noise level as actual target signals, known as false alarms.
To preclude, or minimize false alarms, the radar receiver may be equipped with electronic circuits to establish a false alarm threshold. If the signal strength of a radar return is below this threshold level, it will not be detected or displayed. This false alarm threshold also influences the probability of target detection. With the threshold set too high, many detected targets will not be displayed. Additionally, if the false alarm threshold is raised automatically in relation to the amplitude of the receiver noise, the radar receiver is more vulnerable to noise jamming.
For any target return to be detected by the radar, the S/N ratio must be greater than one. If the S/N ratio is less than one, the target will not be detected above the receiver noise level. The purpose of noise jamming is to raise the level of noise in the radar receiver to reduce the S/N ratio to less than one. This masks the presence of the true target return. If a false alarm threshold is used, noise jamming raises this threshold to further complicate target detection
Jamming-to-signal (J/S) ratio
The jamming-to-signal (J/S) ratio is a fundamental measure of jamming effectiveness. The J/S ratio compares the power in the jamming signal with the power in the radar return. Equation 9-4 is an expression of the J/S ratio. It is important to note that the J/S ratio should be measured at the output of the radar receiver. This will allow consideration of the receiver signal processing gain applied to the jamming signal.
The most critical factor in both the S/N and the J/S ratios is range. The S/N ratio is calculated based on R to the fourth power. This equates to a signal traveling from the radar to the target, and back to the radar receiver. The J/S ratio is calculated using R to the second power. This factor reflects the “one way” transmission of the jamming pulse from the jammer to the victim radar's receiver.
For a jamming signal to be effective, the J/S ratio must be greater than one. In general, threat radars, especially ground-based radars, transmit much more power than does an airborne jamming system. However, this power must travel twice as far as the airborne jamming signal. At long ranges, a low power jamming system can generate a J/S ratio much greater than one. As the jamming system approaches the target, the distance the radar pulse travels decreases with a corresponding increase of power in the radar return. This reduces the J/S ratio to a value less than one and the radar “sees” the target. This is called the burnthrough range.
Burnthrough occurs when the power in the reflected target signal exceeds the power in the jamming signal. Even when an optimum and continuous jamming technique is transmitting on the exact frequency of the victim radar, the jamming starts to lose effectiveness as it nears the radar. For a particular radar jamming technique, burnthrough range depends on the detection capability of the victim radar, expressed as the S/N ratio, and the capability of the aircraft's jamming system, expressed as the J/S ratio. The idea of burnthrough range explains why a jamming technique, especially noise jamming, loses its effectiveness as the aircraft approaches the radar. When plotting the jamming and signal power versus range , these two values intersect at the point where the J/S ratio is one. At closer ranges, the jamming pulse is no longer masking the aircraft, and the aircraft can be detected. Burnthrough range is the point where the radar can see through the jamming.
The purpose of radar jamming is to confuse or deny critical data to the radar systems that play a vital role in supporting the mission of an integrated air defense system. Two types of radar jamming, noise and deception, can be employed in a support-jamming role, or in a self-protection role for individual aircraft. The effectiveness of a jamming technique depends on the ability of the jamming system to generate a jamming signal that replicates the parameters of the victim radar, especially its frequency. The signal-to-noise ratio of the victim radar determines the vulnerability of the radar receiver to jamming while the jamming-to-signaI ratio is an indication of the ability of the jamming system to effectively jam the victim radar. These basic radar jamming concepts are fundamental to understanding the impact of specific jamming techniques on radar systems.
Though late but Indians realised that nations must maintain a formidable military might to ensure peace in our terms. Tough times taught us the importance of indegeneous arms. By the start of the 1980s, the DRDL had developed competence and expertise in the fields of propulsion, navigation and manufacture of aerospace materials based on the Soviet Rockets. Thus, India's political leadership, which included PM Indira Gandhi, Defence Minister R Venkatraman, V.S. Arunachalam (Political Advisor to the Defence Minister), decided that all these technologies should be consolidated. This led to the birth of the Integrated Guided Missile Development Programme with Bharat Ratna Dr. A.P.J. Abdul Kalam, who had previously been the project director for the SLV- Program at ISRO, was inducted as the DRDL Director in 1983 to conceive and lead it.
Initially many western nations formed groups like MTCR to deny advanced top notch technology to prevent India's rise.
To counter the MTCR, the IGMDP team formed a consortium of DRDO laboratories, industries and academic institutions to build these sub-systems, components and materials. Though this slowed down the progress of the program, India successfully developed indigenously all the restricted components denied to it by the MTCR.
Akash, the indigenous supersonic short-range surface-to-air missile (SAM) system, is one of the five missile projects of Integrated Guided Missile Development Programme (IGMDP) of the DRDO. The objective of the project Akash was to develop critical and sophisticated technologies for a ground system and a missile system and integrate these technologies into a state-of-the-art SAM air defence system capable of destroying multiple aerial targets simultaneously.
Akash is a very potent supersonic mobile multi-directional multi-target point/area air defence system that can simultaneously engage several air threats like aircraft, helicopters and unmanned aerial vehicles up to a maximum range of 27 km up to an altitude of 18 km using sophisticated multifunction phased array and surveillance radars in a fully autonomous mode. Builtin ECCM features of Akash facilitate normal function in intense jamming environment.
Three sets of combat elements of weapon systems like Battery Level Radars, Battery Control Centres and
Self-propelled Launchers were made on BMP-I, BMP-II and T-72 chassis with modifications on hulls suitable to fit the equipment. All these systems were used in demonstrating the performance of the weapon system during development and user trials.
A total of 38 vehicle-based systems were developed on both tracked and wheeled vehicles and were used to demonstrate the capability of the system through flight testing of 61 Akash missiles.
The Akash SAM was developed to replace the Russian 2K12 Kub (SA-6 Gainful) missile system, currently in service. The Akash missile can be launched from static or mobile platforms, such as battle tanks, providing flexible deployment. The SAM can handle multitarget and destroy manoeuvring targets such as unmanned aerial vehicles (UAV), fighter aircraft, cruise missiles and missiles launched from helicopters.
The Akash SAM system defends vulnerable areas in all weather conditions against medium-range air targets being attacked from low, medium and high altitudes.
It can operate autonomously, and engage and neutralise different aerial targets simultaneously. The kill probability of the Akash is 88% for the first and 99% for the second missile on a target. The Akash SAM is claimed to be more economical and accurate than the MIM-104 Patriot, operated by several nations including the US, due to its solid-fuel technology. The Akash can intercept from a range of 30km and provide air defence missile coverage of 2,000km².
The Akash SAM system consists of an integral ramjet propulsion, a switchable guidance antenna system, a command guidance unit, an onboard power supply, a system arming and detonation mechanism, digital autopilot, radars and C4I centres.
The most important element of the Akash SAM system battery is its high-power, multi-function Rajendra phased-array radar.
The 3D passive electronically scanned array Rajendra radar (PESA) can electronically scan and guide the missile towards targets. It provides information on the range, azimuth and height of a flying target.
The Akash battery has four Rajendra radars and four launchers interlinked together and controlled by the group control centre (GCC). Each launcher, equipped with three missiles, is controlled by one radar that can track 16 targets.
The Rajendra radar can therefore track 64 targets and simultaneously guide 12 Akash missiles. The PESA antenna array has a swivel of 360° on a rotating platform. The Rajendra radar can detect up to a radius of 80km and can engage at a range of 60km at an altitude of 8km. The communication links, command and control nodes, sensors and self-propelled launchers of the entire Akash SAM system are IT-integrated. The weapons system uses radar vehicles and T-72 tank chassis for launchers.
The Akash missile has a launch weight of 720kg and measures 5.8m in length, 350mm diameter and 1,105mm wingspan. The missile can fly at a speed of up to Mach 2.5 and has a height ceiling of 18km. The 60kg payload can use prefabricated tungsten alloy cubes warheads or a nuclear warhead.
The Akash uses state of the art integral ramjet rocket propulsion system to give a low-volume, low-weight (700 kg launch weight) missile configuration, and has a low reaction time - from detection to missile launch - of 15. It reaches a speed of Mach 1.5 in 4.5 seconds; Mach. 2.8-3.5 at 20g in 30 seconds after ramjet motor is ignited. Its range (for most effective performance) varies 27-30 kilometres. Unlike the Patriot, Akash can be launched from static or mobile platforms, including a battle tank.
The missile can be deployed either in autonomous mode or group mode. In the autonomous mode, it will have a single battery functioning independently. For surveillance, it would need an additional two-dimensional radar. In this mode, it can be used for defending moving columns or singular installations. A single battery can simultaneously engage four targets, and against each target a maximum of three missiles can be fired, thus increasing the hit probability.
In group mode, there would be a number of batteries, deployed over a wide area. The batteries would be linked to a group control centre (GCC). The Rajendra three-dimensional radar would provide a single integrated air picture to the group control centre, telling it not only the distance at which the enemy plane has been located but also its altitude. One GCC can command and control a maximum of eight Akash batteries at the same time. One GCC can also receive radar surveillance information from other sources, and be linked to higher echelons of air defence. Once the target, either an enemy aircraft or a missile, is detected the missile would align to the radar beams and virtually travel on those beams (guided by onboard precision-homing system) towards the target at three-and-a-half times the speed of sound. Its radars could be placed on a civil aircraft, much like an AWACS system, to provide early warning of incoming missiles.
The missile is guided by a phased array fire control radar called 'Rajendra' which is termed as Battery Level Radar (BLR) with a tracking range of about 60 km. The tracking and missile guidance radar configuration consists of a slewable phased array antenna of more than 4000 elements, spectrally pure TWT transmitter, two stage superhetrodyne correlation receiver for three channels, high speed digital signal processor, real time management computer and a powerful radar data processor. It can track 64 targets in range, azimuth and height and guide eight missiles simultaneously in ripple fire mode towards four targets. The radar has advanced ECCM features. The Rajendra derivative on a BMP-2 chassis and to be used by the Indian Air Force is known as the Battery Level Radar-II whereas that for the Army, is based on a T-72 chassis and is known as the Battery Level Radar-III.
The Army version also consists of the Battery Surveillance Radar (BSR). BSR is a track vehicle based, long range sensor, interfaced with the BCC. It can detect and track up to 40 targets in range and azimuth up to a range of 100 km.
Long range target acquisition is performed by the 3D Central Acquisition Radar (3D CAR), which is a long range surveillance radar that can track up to 200 targets in Track while Scan mode (detecting, tracking and processing) in three dimensions at a range of 180 km. It provides azimuth, range and height coordinates of targets to the Group Control Centre (GCC) through secure communication links. The data is used to cue the weapon control radar.
Rajendra is a slewable passive phased array radar used for 3-D target detection, multi target tracking and multiple missile guidance under extreme hostile EW environment. It makes use of a passive phased array to search a volume of space, distinguish between hostile and friendly targets, automatically track up to 64 targets and command one of several launchers to engage up to 4 targets simultaneously. Initially designed as a standalone system, Rajendra is now equipped with the ability to integrate with a network of sensors, including long and medium-range surveillance radars of foreign and indigenous origin.
Rajendra's multi-element antenna arrangement folds flat when the vehicle is in motion. The Radar consists of a surveillance antenna array with 4000 phase control modules (PCM's) operating in the G/H-Band (4-8 GHz), engagement antenna array with 1000 PCM's operating in the I/J-Band (8-20 GHz), a 16-element IFF array and steering units. A powerful high-end computer computes phases for all the elements of the array. Rajendra controls the beam positioning sequence through beam requests for each track at adaptive data rates and performs multifunctional roles like search –confirm –track -interrogate targets, assign and lock on launchers, and launch/acquire/ track/guide missiles. The RDP supplies track data to remote group control centre. Rajendra features a Dual channel radar receiver and a C band transmitter, although the complete transmitting and receiving features and bands are unknown.
Rajendra radar uses phase shifters integrated in large numbers for electronic beam steering. This allows Rajendra radar to simultaneously track multiple aircraft and also guide multiple missiles towards these targets. The phase shifter was designed and developed by Prof Bharati Bhat, a scientist from Centre for Applied Research in Electronics (CARE) of IIT, Delhi, and her team.
The phased array radar rotates 360 degrees on a rotating turnstile at a moderate speed. This allows it to perform 360 degree surveillance. The phased array itself has 45 degree scan limits to either side, giving a total scan coverage of 90 degrees, if the radar array is static.
During Multisensor Tracking a 2-D battery surveillance radar (BSR) with 360 degree coverage and a larger detection range provides track data to the multifunction, slewable, 3-D phased array radar. This is useful when a single battery of the Rajendra is detached from the group to fight alone, and early warning from the 3-D CAR is not available. The 2-D BSR data is then integrated by the Rajendra's radar vehicle. The multisensor direction finder in Rajendra processes the track data from the phased array radar and the BSR to identify the targets reported by both the sensors and maintains a common track database. For those BSR tracks, which are not being reported by Rajendra though under its coverage, target acquisition is initiated with elevation search in the designated direction. The antenna is skewed in the direction of threat to acquire the targets, which are outside the covered air space. The Rajendra's tracking range is 60 km against fighter aircraft flying at medium altitude.
The major functions of the Rajendra are:
Central acquisition radar (3D-CAR)
The central acquisition radar (3D-CAR) is a 3D radar developed by DRDO capable of tracking 150 targets.
India has further developed its 3D CAR into all new ROHINI & REVATHI variants. The ROHINI is the Indian Air Force specific variant, whereas the REVATHI is for the Indian Navy. These replace the original joint development items such as the planar array antenna with new locally developed ones which are more capable than the original design. A third variant, known as the 3D Tactical Control Radar has been developed for the Indian Army and has cleared trials.
Central acquisition radar (CAR) is a medium-range high-resolution 3D surveillance radar. Central acquisition radar was designed by LRDE, a DRDO laboratory, and is produced by a joint venture between BEL, Larsen & Toubro, Astra Microwave and Entec. The radar employs a planar array antenna and provides simultaneous multi-beam coverage. It can handle 150 targets in track while scan mode.
The prefragmented warhead of the Akash missile is coupled with a digital proximity fuse. The detonation sequence is controlled by safety arming and a detonation mechanism. The missile is also integrated with a self-destructive device. Unlike the Patriot missile, Akash uses a ramjet propulsion system which gives it thrust to intercept the target at supersonic speed without any speed deceleration. The terminal guidance system of the missile enables its working through electronic countermeasures. The Rajendra radar completely guides the Akash missile, which increases its efficacy against electronic jamming of aircraft. The missile can carry a 60 kg warhead.
The SYSTEM TRIALS
Interception of moving aerial targets with Akash missile system was demonstrated through various flight tests in different mission profiles like:
(a) Interception of far boundary targets
(b) Near boundary targets
(c) High altitude targets
(d) Crossing and receding targets
(e) Ripple mode firing on approaching and receding targets
(f) Multiple target interception
(g) Low altitude far boundary interception, and
(h) Low altitude and near boundary interception.
The system was also subjected to Electronic Warfare (EW) trials for proving the system resistance in intense jamming environment. Flight tests were conducted with deliverable production equipment of the Indian Army and IAF demonstrating target interceptions at low altitude near boundary UAV and precision guided bomb SPICE 2000 earning the satisfaction of the users.
PARTNERS IN DEVELOPMENT
Akash system is the outcome of successful partnership of Defence Research and Development Laboratory
(DRDL), the nodal DRDO laboratory, along with 13 other DRDO laboratories; 19 Public Sector Units (PSUs) including Bharat Dynamics Limited (BDL), Bharat Electronics Limited (BEL), Hindustan Aeronautics Limited (HAL), Electronics Corporation of India Limited (ECIL), Heavy Vehicles Factory (HVF), Central Electronics Limited (CEL); major Private Industries like Tata Power SED, L&T; six Ordinance Factories, viz.,Itarsi, Khamaria, Bhandara, Medak, Chanda and Dehu Road; three national laboratories; six academic institutions, viz., IIT Delhi, IIT Madras, IIT Mumbai, IIT Kharagpur, IISc Bangalore and Jadavpur University; and more than 265 private sector industries across the country.
Some of the indigenous technologies developed by DRDO during the programme are: integral ram rocket propulsion system, multifunction phased array radar system, multi beam 3D surveillance radar system,
C4I system hardware and software for air defence application, command guidance system, dual control digital autopilot and PN guidance, digitally coded radio proximity fuze, electrical servo drive system, frequency hopping communication system, switchable guidance antenna system, built-in ECCM features for guidance, digital coded guidance schemes for multiple missile tracking, end game techniques for maximizing effectiveness of kill, multi-radar tracking and fusion of tracks, five-stage safety arming mechanism, dual frequency generating power supply system, digital signal processing techniques, software algorithms for automatic controlling of weapon system and simulators and training aids to demonstrate capability of system.
Based on the performance of system demonstrated through user evaluation trials, user field trials and flight tests, the system was formally inducted into Indian Army on 5 May 2015 and into the IAF on 10 July 2015. Production order worth Rs 20,000 crore was placed by the IAF and the Indian Army. Seeing the performance of Akash radars, Indian Armed Forces also placed orders for Akash offshoot products like Rohini, Revathi and the Weapon Locating Radars.
Akash missile system is produced by nodal production agency Bharat Electronics Limited (BEL), Bengaluru
for IAF and Bharat Dynamics Limited (BDL), Hyderabad, for Indian Army. Radars and radar-related equipment are being produced by BEL. While missiles and their related equipment are being produced by BDL, the launchers are being produced by Tata Power SED and M/s L&T. The control centres are produced by ECIL.
About 300 MSMEs are involved in continuous production of components/ sub-systems/modules for Akash Missile System. The programme has ensured that the industry partners involved in development were also given preference for production. Additional industry partners were developed in some cases where the rate of production was required to be enhanced . During the production, DRDO revamped radars, control centres, launchers with re-engineering of system on trailers and high mobility (Tatra) vehicles as per the requirement indicated by the IAF and the Indian Army. Some performance enhancement features, which were demonstrated through flight testing, were added on deliverable production version equipment. Since, for the first time production of an indigenous SAM system of this magnitude was being attempted, DRDO guided all the stakeholders (DRDO labs, BEL, BDL, OFs, inspection agencies, industries and the users) towards successful production, inspection, testing, and validation.
Production of Akash missiles for Indian Army are being continuously monitored by the Project Group. Order worth Rs 5,500 crore for seven Squadrons (14 FUs) of Akash is expected by March 2018. Request for Proposal for two more Regiments of Akash Weapon System (with RF seeker missiles) worth about Rs 10,000 crore is also expected from the Indian Army. Eight (8/8) Squadrons of Akash missile system and six (6/12) Troops have been delivered to the IAF and the Indian Army, respectively. Infrastructure was created at user’s sites for storage, deployment, operation and maintenance of the system through lead production agencies. Supply chain or special surface-to-air weapon system elements like surveillance radars, missile guidance radars, launchers, control centres, missile subsystems, ground support systems, etc., have been established with stringent aerospace/military grade requirements. Realization of missile guidance radars (28/28), launchers (112/112), control centres (28/28), surveillance radars (22/22) has demonstrated DRDO’s commitment to the ‘Make in India’ initiative of the government.
The DRDO created revenue of about Rs 38,000 crore through Akash missile system and its offshoot products, which is a commendable achievement for indigenous design and development. DRDO has also gained the experience of generating technology transfer documents for manufacturing, inspection, testing, and integration of the surface-to-air weapon system. DRDO also gained the experience of handling and guiding all the stakeholders at various critical stages of production, inspection, integration and acceptance. The Akash Missile System is today proudly safeguarding important defence assets of the country.
The development of the weapon system's next generation is currently underway.
Main Material Source :-
Air force Technology
Once a target has been designated, acquired, and tracked by a radar system, the final stage in target engagement is to guide a missile or projectile to destroy the target. There are three basic requirements for successful missile guidance:
There are three distinct phases in any missile intercept: boost, mid-course, and terminal.
Nearly all missiles are unguided during the initial boost phase. During the boost phase, the missile electrical and hydraulic systems are activated and are coming up to operating parameters. The missile is gathering speed and normally will be in an unguided mode of flight.
During the mid-course phase, the missile is actively being guided to the target using some type of guidance signal. Guidance signals deflect the control vanes of the missile to change its direction. These vanes change the roll, pitch, and yaw, in some combination, to control the missile flight path. Normally a gas grain generator powers a small hydraulic pump that deflects the control vanes in response to guidance signals. Each missile carries a limited supply of hydraulic fluid for maneuvering. The fluid is expended through vents with every control surface activation. The limited quantity of hydraulic fluid can be a significant factor during a long-range missile intercept.
The final phase of an intercept is the terminal phase. During this phase, the missile attempts to pass close enough to the target to detonate the fuse while the target is within the lethal radius of the warhead. Modern missiles employ both a contact fuse and some type of proximity fuse. Proximity fuses range from command detonation for command-guided missiles, fractional Doppler gates for semi-active guided missiles, to active laser fuses for IR-guided missiles.
Command guidance uses a fire control computer to constantly send course correction commands to the missile throughout its flight. These commands are a series of electrical missile guidance pulses called doublets or triplets. These pulses provide steering commands to the missile by varying the spacing between each guidance pulse. Each pulse, or pulse combination, relays some roll, pitch, and yaw command to the missile. These inputs are constantly corrected for the spatial relationship between the missile and the target's present position and rate of motion. Guidance commands are passed to the missile by specialized antennas on the TTR and an antenna installed on the missile, called a missile beacon. The beacon is a special radio receiver and transmitter that is attached to the rear of the missile. It acts like a transponder in that the TTR tracks and receives guidance commands. The guidance frequency may be widely separated from the target tracking radar frequency to minimize interference. This beacon is usually masked until missile booster separation. These results in the missile being launched unguided for the first 2-3 seconds. This type of delay is one of the reasons that all command-guided missile systems have a minimum launch range.
Command-guided missiles will generally fly a rectified (full or half) or threepoint pursuit geometry during the mid-course portion of the intercept. However, a command-guided missile may transition to pure pursuit geometry during the terminal phase of the intercept. Rectified geometry involves the prediction of where the target and the missile will be at some point in the future.
The target's direction and rate of movement is tracked and predicted. The missile is then launched, pulls lead on the target, and is guided to the point in the sky where the intercept is predicted to take place. This profile requires the constant update of both the target and missile positions.
Three-point pursuit geometry is often used when there is incomplete range tracking data on the target. In this case, it will be impossible to predict exactly where the target will be at some point in the future. In this profile, the target tracking radar constantly tracks the target. The missile location will be updated by the missile beacon. The fire control computer will direct the missile to fly directly down the tracking radar beam toward the target. In this geometry, the missile may start out on a direct intercept course and, depending on the target's direction and rate of movement, transition to a pure pursuit intercept. The three points in three-point missile geometry are depicted in Figure. Point one is the target tracking radar, point two is the missile itself, and point three is the target.
By keeping all three points always in a line, the missile will intercept the target at some point, although the range of the target is unknown.
Command guidance techniques have many advantages. First, command guided missiles can adjust their flight geometry throughout an intercept profile.
Second, the missiles are uncomplicated since they do not carry onboard computers or target tracking equipment. The fire control computer associated with the TTR accomplishes all intercept calculations. Third, the primary intercept profile, a full- or half-rectified intercept, is the fastest and most fuel-efficient intercept. Fourth, command guidance is difficult to jam since the missile beacon antenna is at the rear of the missile and can be relatively high-powered. And finally, an intercept is possible even without accurate range information by using the three point intercept profile.
Command guidance has several disadvantages. First, the use of a missile beacon delays the capture of the missile by the tracking radar. This can cause a large dead zone which equates to a larger minimum engagement range. Second, the accuracy of the intercept geometry is only as good as the tracking information provided by the target tracking radar. Jamming, interference, or loss of signal will adversely affect the intercept accuracy. In addition, normal radar characteristics could produce sufficient errors to cause the missile to miss the target, especially at longer ranges. Third, with insufficient range information, the three-point intercept profile is very slow and could result in the missile running out of energy before it gets to the target. Fourth, command guidance is reactive. The fire control computer constantly updates the intercept geometry based on target maneuvering. This results in missile maneuvering lagging target maneuvers.
Semi-active guidance is significantly different from command guidance, but only after launch. The first requirement is still for the target tracking radar to maintain a solid target track, with the tracking data being supplied to the fire control computer. The fire control computer then directs a target illumination antenna to point at the target and illuminates it with CW energy. The missile then passively homes on the reflected CW energy.
The missile used by a threat system that uses CW homing is vastly different from the missile being guided by a command guidance signal. The missile that homes on CW energy must be equipped with a seeker section composed of an antenna and an internal receiver. The seeker section processes and computes the necessary course corrections as it flies toward the target. It can do this by knowing the zero boresight line of the antenna within the missile. As the reflected CW energy is received by the seeker, there is normally some deviation from the zero reference position. The onboard computer then directs the control surfaces to change the flight path to reduce the reference errors in the antenna to zero, if possible. When the error between the antenna position and the boresight position is zero, the missile is pointed directly at the target.
Missile systems that use semi-active guidance normally use velocity as the primary target discriminator during the intercept. The missile seeker locks onto a reference Doppler signal provided by the fire control computer before launch. This Doppler signal establishes a tracking gate around the velocity of the target.
After the missile is launched, it initially compares the reference Doppler to the target Doppler signal.
The mid-course phase for a semi-active missile is also different from that of a command-guided missile. A semi-active guided missile follows the reflected CW energy during the mid-course phase of the intercept and normally attempts to fly a lead pursuit profile to the target. If the target maneuvers, however, the missile may transition to a pure pursuit flight path. Unlike a command-guided missile, a semi-active guided missile does not use a missile beacon. The fire control computer does not need to know where the missile is to compute course corrections since all that is necessary is to illuminate the target with the CW illuminator. This also means that the missile can begin to track and guide when it is launched and locked on to the reference Doppler gate. Semi-active guidance is the primary mode of guidance for many surface-to-air missiles, and radar-guided air-to-air missiles.
As the missile enters the terminal phase of the intercept, there is no change in the guidance mode used by a CW homing missile. The missile may complete the terminal phase of the intercept geometry by going to a pure pursuit flight path, if necessary. The missile continues to home in on the reflected CW signal until it passes close enough for the fuse to function.
Semi-active missile guidance has many advantages. First, a semi-active guided missile is resistant to electronic jamming that may be used to deny range information. Second, a semi-active missile can be guided almost immediately after launch. This gives it a very small minimum range since it can maneuver almost as soon as it clears the launch rail. Third, it computes its own course corrections as necessary. This allows for a much quicker reaction to target maneuvers compared to a command-guided missile. Fourth, during a long-range intercept, a CW missile can be more accurate than a command-guided missile.
This is accomplished by taking the inherent long-range radar tracking errors out of the equation. The target tracking radar only has to keep the target illuminated so that it can point the CW antenna at the target.
Although semi-active missile guidance is generally considered an excellent guidance technique, it does have some disadvantages. First, a semi-active guided missile normally requires reference Doppler values to be entered into the missile computer before launch. Without this reference, a semi-active missile cannot be launched. Second, a semi-active homing missile must maintain a lock onto the target Doppler. The use of chaff and beam maneuvers, which result in a near zero target Doppler, may cause a missile or radar to break lock. Third, if a break-lock occurs, a CW homing missile normally cannot regain target track and complete the intercept.
This specialized guidance mode is only active during the terminal phase of flight. The mid-course phase usually employs semi-active or command guidance. The range at which the missile goes “active” is dependent on the intercept geometry. High-aspect angle intercepts allow the activation of active guidance sooner than beam or tail-aspect intercepts. Missiles that employ active guidance carry a complete miniature radar system and fire control computer within the missile. As the missile nears the target, its internal radar system turns on and locks onto the target. The internal fire control computer directs control inputs to complete the intercept
Active-guided missiles have many advantages. First, active-guided missiles are very accurate at long ranges. This is because they do not rely on the target tracking radar once their internal radar takes over the intercept. Second, an active missile is extremely difficult to jam. It uses a narrow beam and its relative power is constantly increasing as it nears the target. Third, an active-guided missile is a fire-and-forget weapon. Command or semi-active missile guidance requires the target tracking radar to maintain lock-on until the intercept is completed. In an air-to-air engagement, this means the interceptor is predictable until the missile hits the target, and vulnerable to an enemy missile attack. An interceptor with an active missile, however, may launch the missile and, once it goes “active,” can then turn around or maneuver defensively.
Active-guided missiles have a few disadvantages as well. First, the active homing missile is a complex missile integrating both command and active guidance modes. Second, the missile may still be susceptible to electronic jamming during the mid-course phase of flight. Remember, during the mid-course phase, the missile relies on command or semi-active guidance. Jamming the target tracking radar may affect the missile's ability to “see” the target near the terminal phase.
SEEKER-AIDED GROUND GUIDANCE/TRACK-VIA-MISSILE GUIDANCE
In seeker-aided ground guidance (SAGG) and track-via-missile (TVM) guidance, the target is illuminated by the ground-based radar and the missile receives reflected energy from the target. Unlike conventional semi-active homing, the missile does not generate its own guidance commands. Instead, the missile transmits raw engagement data to the ground-based fire control system (FCS) in order to generate uplink guidance commands. TVM is similar to SAGG; however, additional processing is done on-board the missile prior to transmitting the engagement data to the ground-based FCS.
Track-via-missile and seeker-aided ground guidance are two relatively new missile guidance techniques with similar advantages. First, they are extremely accurate at long ranges where the inherent radar tracking errors may be large enough to cause a miss. Second, they can respond very quickly to any actions taken by the target since the missile seeker can track these changes and transmit the new position to the TTR fire control computer. Third, TVM and SAGG can be used with a large and capable fire control computer since most computations are accomplished by the TTR. Fourth, the integration of phased array radar and the powerful TTR fire control computer allows the missile system to engage multiple targets. The Patriot missile battery, for example, can track and engage at least four targets simultaneously.
The major disadvantage of track-via-missile and seeker-aided ground guidance is that they are the most complex forms of missile guidance. They require the use of sophisticated computers to combine radar tracking data and data received from the missile. This required hardware is expensive and demands greater maintenance and logistical support. In addition, the missile itself needs to be large enough to store the appropriate hardware for computations and data transfer.
A target tracking radar (TTR) or Fire-control radar is designed to provide all the necessary information to guide a missile or aim a gun to destroy an aircraft. Once a target has been detected, either by dedicated search radar or by using an acquisition mode, the TTR is designed to provide accurate target range, azimuth, elevation, or velocity information to a fire control computer.
A typical TTR has individual tracking loops to track a target in range, azimuth, elevation, or velocity. The antenna of the TTR is pointed at a single target, and the radar initiates acquisition and target track. TTRs normally employ automatic trackers to continuously measure target data. The range tracking loop employs an early gate/late gate range tracker to maintain automatic range tracking. The azimuth and elevation tracking loops generate error signals to position the antenna and maintain constant target illumination. The velocity tracking loop found on pulse Doppler and CW radars is used to reject clutter and generate accurate target radial velocity information. All this critical information is passed to a fire control computer for weapons employment.
The fire control computer is programmed with critical information on the capability of the weapon to be employed. For a missile, the fire control computer is programmed with the aerodynamic and range capabilities of the missile. For antiaircraft artillery (AAA), the fire control computer is programmed with the ballistics for the gun, rate of fire, and tracking rate. The fire control computer uses the precise target information from the TTR and the programmed weapon's parameters to compute a firing solution. Once a firing solution has been computed, the fire control computer either fires the weapon automatically or alerts the operator, who fires the weapon. For missile employment, the fire control computer may continue to provide missile guidance and fusing commands until missile impact or initiation of an active missile guidance mode.
For AAA engagement, the fire control computer computes the required lead angle, aims the guns, and initiates firing.
To provide the required azimuth and elevation resolution, most TTRs use a high frequency to provide narrow antenna beamwidths for accurate target tracking. High frequency operation also allows the radar to transmit wide bandwidths. To provide the required range resolution, most TTRs employ narrow pulse widths and high pulse repetition frequencies (PRFs) to rapidly update target information.
In most TTR applications, the target is continuously tracked in range, azimuth, and elevation. Range tracking can be accomplished by an operator who watches an “A” scope presentation and manually positions a hand wheel to maintain a marker over the desired target return. The setting of the hand wheel is a measure of target range and is converted to a voltage used by the fire control computer.
As target speeds and maneuvers increase, the operator may have extreme difficulty maintaining manual target range tracking. To avoid this situation, most TTRs employ an automatic range tracking loop. All pulse TTRs, which includes conical scan, track-while-scan, monopulse, and pulse Doppler radars, employ either a split gate or leading-edge automatic range tracking system. In a TTR, automatic range tracking serves two essential functions: (1) it provides the critical value of target range, and (2) it provides a target acceptance range gate that excludes clutter and interference from other returns. Since radar range is normally the first target discriminator used to initiate automatic target tracking, the second function is essential to the proper operation of the other tracking loops.
A range gate circuit is simply an electronic switch that is turned on for a period of time after a pulse has been transmitted. The time delay for switch activation corresponds to a specific range. Any target return that appears inside this range gate is automatically tracked. The most common type of automatic range tracking is accomplished by a split-gate tracker.
The automatic range tracking loop attempts to keep the amount of energy from the target return in the early gate and late gate equal. The range tracking error is computed by subtracting the output of the late gate from the output of the early gate. The amount of the range tracking error signal is the difference between the center of the pulse and the center of the range gate. The sign of the error signal determines the direction in which the gates must be repositioned to continue to track the target.
Leading-edge range tracking is an electronic protection (EP) technique used to defeat range-gate-pull-off (RGPO) jamming. The leading-edge tracker obtains all range data from the leading edge of the target return. All RGPO cover pulse jamming tends to lag the target return by some increment of time. By differentiating the entire return with respect to time, the target return can be separated from the jamming pulse. Employing a split-gate tracker electronically positioned at the initial pan, or leading edge, of the returning pulse, the range tracking loop can track the target return and ignore any jamming signals. The range tracking loop then uses split-gate tracking logic to determine the magnitude and direction of range tracking errors and reposition the range gate.
The width of the tracking gate is an important radar design consideration. The range gate should be sufficiently narrow to effectively isolate the target from other returns at different ranges. It should be wide enough to allow sufficient energy from the target echo to be displayed. The width of the range tracking gate is normally equal to the pulse width of the radar.
Nearly all range tracking gates employ some form of automatic gain control (AGC). AGC is designed to limit target clutter and glint. It is also designed to avoid excessive false alarms.
TWS is a combined search and tracking mode that sacrifices the continuous target observation capability of the dedicated tracker in return for the ability to monitor a finite sector of airspace. This is accomplished while maintaining tracks on multiple targets moving through the covered airspace. There are two types of radar systems capable of TWS operation: conventional and phased array.
Conventional track-while-scan threat radars use two separate antennas to generate two separate beams. These beams operate at two different frequencies and are sectored so they overlap the same region of space. This overlap area provides a tracking area for a single target. One beam is sectored in the vertical plane to give range and elevation. The other beam is sectored in the horizontal plane to provide range and azimuth. Each beam scans its sector at a rate of 5 to 50 times per second. This provides a rapid update on target range, azimuth, and elevation.
TWS is a combined search and tracking mode that sacrifices the continuous target observation capability of the dedicated tracker in return for the ability to monitor a finite sector of airspace. This is accomplished while maintaining tracks on multiple targets moving through the covered airspace. There are two types of radar systems capable of TWS operation: conventional and phased array.
Conventional track-while-scan threat radars use two separate antennas to generate two separate beams. These beams operate at two different frequencies and are sectored so they overlap the same region of space. This overlap area provides a tracking area for a single target. One beam is sectored in the vertical plane to give range and elevation. The other beam is sectored in the horizontal plane to provide range and azimuth. Each beam scans its sector at a rate of 5 to 50 times per second. This provides a rapid update on target range, azimuth, and elevation.
The two TWS antennas generate their beams using an electromechanical principle. Each antenna provides inputs to its own display and provides angle and range information for all targets in the coverage of the radar. The display from the elevation beam is calibrated in range and elevation, while the display from the azimuth beam is calibrated in azimuth and range. Operators position a cursor over the returns on these displays using range as the primary parameter. Once a target has been designated for engagement, the radar automatically attempts to keep the tracking axis of the radar beams centered on the target.
Once the target is designated by the operator, the range gate is enabled and tracks the target using a split-gate tracker. The azimuth and elevation tracking loops receive information only from targets inside the range gate. As the beams scan across the target, a burst of pulse returns is received that have an amplitude envelope corresponding to the beam pattern.
The azimuth tracker is typically a split-gate tracker, identical in concept to a split-gate range tracker. However, range delay time is replaced by azimuth scan time. The azimuth tracker uses a left gate and right gate. Each gate integrates its share of the target return to generate a voltage/time value. When the azimuth gate is centered on the target, the areas are equal and the error signal (right gate minus left gate) is zero. The azimuth tracking loop sends signals to the antenna servos to keep the target centered in the scan area.
Elevation tracking is accomplished in the same manner by using an up gate and a down gate. The elevation tracking loop also sends signals to the antenna servos to keep the target centered in the scan area.
Once the target is designated and the radar is automatically keeping the radar return centered in the tracking area, target range, azimuth, and elevation information is sent to a fire control computer. The radar continues to provide information on other targets in the scan area. The fire control computer indicates the firing solution has been achieved for the designated target, and a missile is launched. The radar tracks the target and the missile and provides in-flight corrections to the missile right up to the moment of missile impact. These corrections are based on both target and missile azimuth, range, and elevation information. Information is passed to the missile from a dedicated antenna on the radar to special antennas on the missile. Commands from the radar to the missile are called uplink guidance commands. Information from the missile back to the radar and fire control computer is called downlink information.
The advantages of a conventional TWS radar include the following:
The primary disadvantages of a conventional TWS radar include:
(1) A large resolution cell due to the wide azimuth and elevation beams, and
(2) Vulnerability to modulation jamming based on the scan rate of the independent beams.
Many modern radars employing a planar or phased array antenna system have a TWS mode. The radar does not really track and scan simultaneously, but rapidly switches between search and track
The most common air-to-air radar system uses a planar array antenna. In the scan mode, the radar antenna generates a pencil beam and uses a raster scan to detect targets in the search area. Targets detected are presented to the pilot on the aircraft's radar display.
In the track mode, the antenna generates multiple beams to illuminate individual targets. The radar typically uses monopulse or pulse Doppler techniques to update target range, azimuth, elevation or velocity.The radar initiates a track file on each detected target that contains all current data on the target and an estimate of future target position.
As the radar switches between track and scan modes, target parameters are updated in the tracking loop. The new target information is compared to the predicted information in the measurement data processing cell. If the two sets of data agree within certain limits, target position and information are updated. This process is called gating.
If the updated target information does not correspond to the predicted values, the information is sent to the correlation processor. The correlation processor attempts to resolve the conflict based on further refinement of target data. If the correlation processor cannot assign the target parameters to an existing track file, a new track file is generated and displayed.
The obvious advantage of a planar/phased array TWS radar is that it can search a large volume of airspace while tracking individual targets. The number of targets that can be tracked is limited by the number of beams the radar can generate. Planar/phased array radars have increased peak and average power when compared to pulse radar systems. Since the radar beam of a planar/phased array radar is electronically controlled and can rapidly change beams and scans, it is resistant to many jamming techniques. The primary disadvantages of a planar/phased array TWS radar include its complexity, cost, and reliance on computer processing.
LORO is a mode of radar operation developed as an EP feature for a track-while scan radar. LORO can be employed by any radar that has the capability to passively track a target. In a LORO mode, the radar transmits a continuous signal from a set of illuminating antennas. This continuous signal hits the target, and the return echo is received by a different set of receive antennas .
The receive antennas are passive and generate azimuth and elevation tracking signals by electronically scanning the reflected signal. The tracking signals are sent to the antenna servos to keep the illuminating antennas pointed at the target and centered in the receive antenna tracking area. The range tracking circuit uses the time delay between the transmission and reception of the illuminating antenna signals. A split-gate tracker is used to provide range tracking.
The illuminating antennas used in the LORO mode have very narrow beam widths and transmit at a high power level. This reduces the effectiveness of noise jamming techniques against a radar employing a LORO mode. In addition, the continuous signal from the illuminating antennas negate the effectiveness of most angle deception jamming techniques designed to defeat TWS radars. These specialized jamming techniques exploit the scan rate of TWS antennas. In the LORO mode, the illuminating antennas do not have a scan rate. The limited effectiveness of both noise and deception jamming techniques is the major advantage of the LORO mode.
The LORO mode also provides a track-on-jam (TOJ) capability to exploit noise jamming techniques. In a TOJ mode, the receive antennas passively track any detected noise jamming signals. The radar assumes that the most intense jamming signal is the target. The receive antennas process the strongest jamming signal as if it were a target echo from the transmit antenna signal. The receive antennas generate azimuth and elevation tracking signals to keep the jamming signal centered in the tracking area. The TOJ mode does not provide target range.
Scan pattern referring to how radars steer their beam across their field of view to search for targets
A circular scanning radar uses an antenna system that continuously scans 360° in azimuth . The time required for the antenna to sweep one complete 360° cycle is called the scan rate. Scan duration is the number of “hits per scan,” or the number of pulses, reflected by a target as the radar beam crosses it during one full scan. Most pulse radars require 15 to 20 hits per scan to obtain sufficient information to display a target. The factors that determine the number of hits per scan the radar receives include pulse repetition frequency (PRF), antenna beamwidth, and scan duration.
Circular scan radars provide accurate target range and azimuth information. This makes these radars ideal for the roles of early warning and initial target acquisition. To accomplish these missions, the antenna generates a fan beam that has a large vertical beamwidth and a small horizontal beamwidth. Since elevation information will normally be provided by height finder radars, the size of the vertical beamwidth is not a limitation. This antenna scan allows the radar to scan large volumes of airspace for early target detection. Since early detection is the primary goal of early warning radars, accurate altitude and azimuth resolution are secondary considerations.
Circular scan radars designed for early warning transmit a radar signal with a low PRF. A low PRF allows sufficient time for the radar pulse to travel long distances, and return, before another pulse is transmitted. This gives the radar system a long, unambiguous range capability. Circular scan radars with low PRFs generally use long pulse widths in order to increase their average power and long-range detection capability. The scan durations of early warning radars are relatively long to provide the required “hits per scan” for long-range target detection. The plan position indicator (PPI) scope display is normally used with circular scan radar
In order to provide coverage for a large volume of airspace, the beamwidth associated with circular scan radar is relatively wide. This wide beamwidth, coupled with the long pulse width and low PRF, gives the circular scan radar a large resolution cell, especially at long ranges. This limitation can be exploited to mask force size and composition. However, as range decreases, the dimensions of the resolution cell decrease, and circular scan radar will begin to break out target formations.
Circular scan radars provide range and azimuth information for both early warning and acquisition roles. Modified circular scan radars that can also provide elevation information may be used for ground control intercept (GCI) roles. Two modified circular scan radars that determine range, azimuth, and elevation are the V-beam and the stacked beam.
The V-beam radar transmits two fan-shaped beams that are swept together. A vertical beam provides range and azimuth information. A second beam, rotated at some convenient angle, provides a measure of the altitude of the target.
A stacked beam radar employs a vertical stack of fixed elevation “pencil” beams which rotate 360°. Elevation information is obtained by noting which beam contains the target return. Range and azimuth information is determined in the same manner as in an early warning radar.
Linear scan is a method used by some radar systems to sweep a narrow radar beam in a set pattern to cover a large volume of airspace. Linear scans can be oriented in a vertical direction for height finder radars or in a horizontal direction, or raster, for acquisition and target tracking radars. Unidirectional linear radar scans in a single direction then begins its sweep all over again. Generally, linear scans offer excellent single-axis coverage, and the narrow beam offers enhanced azimuth and elevation resolution.
A helical scan is a unidirectional scan pattern that allows a “pencil” beam to search a 360° pattern. The antenna sweeps a 360° sector in a clockwise direction. After each complete revolution, the antenna elevation is increased. This scan pattern is repeated for a specified number of revolutions, in this case, three, 360° sweeps. At the end of the scan pattern, the antenna elevation is reset to the initial elevation and the scan is repeated. A helical scan pattern is commonly used as a target acquisition mode for radar systems with narrow vertical and horizontal beamwidths.
A bidirectional linear scan, such as a raster scan, sweeps both horizontally and vertically. A raster scan uses a thin beam to cover a rectangular area by horizontally sweeping the area. The angle of elevation is incrementally stepped up or down with each horizontal sweep of the desired sector. After the sector has been covered, the angle of elevation is reset to the original value and the process is repeated. The number of raster bars is set by the number of horizontal sweeps in the basic raster pattern. Shows a four-bar raster scan, which is normally associated with airborne interceptor (Al) radar.
A conical scan, or conscan, radar is generally used for precision target tracking. A conical scan radar employs a pencil beam of radar energy that is continuously rotated around the target. This circular rotation of a pencil beam generates a cone-shaped scan pattern with the apex of the cone located at the antenna. Thus, the name conical scan.
As the pencil beam rotates, the circular scan patterns overlap in the center. This creates a central tracking area that has a much smaller effective beamwidth than the rotating pencil beam. This results in a very precise tracking solution.
Since conical scan radars are designed for precision target tracking, these radars normally operate at high frequencies, high PRF, narrow pulse widths, and narrow beamwidths. The rotation rate of the pencil beam can exceed 1,800 revolutions per minute. This means that both azimuth and elevation data can be updated about 30 times per second.
The combination of conical scan and raster scan is called a Palmer-raster scan. A Palmer-raster scan uses a thin beam, employing a conical scan searching pattern, for a specific sector of airspace. With each sweep of the sector, the angle of elevation is incrementally stepped up or down. After the vertical sector has been covered, the angle of elevation is set at the original elevation and the process is repeated. The number of bars is determined by the number of vertical search scans.
The combination of a conical scan and a circular scan is called a Palmer scan. Palmer scans incorporate a circular scanning antenna to search the entire horizon while simultaneously performing a conical scan. If the radar antenna is also performing a unidirectional altitude search in conjunction with this scan, it is employing a Palmer-helical scan.
A track-while-scan (TWS) system uses a technique that allows a radar to track one or more targets while scanning for others. Radar systems with a TWS capability must be able to generate two or more distinct radar beams.
A conventional TWS radar employs two antennas that work with each other to perform the scan function . Each antenna produces a separate unidirectional beam. Each beam is transmitted at a different frequency. The vertical antenna generates a beam employing a vertical sector scan similar to height finder radar except the beamwidth is narrower and it scans at a higher rate. The horizontal antenna generates an identical beam employing a horizontal sector scan at a different frequency. The track function is accomplished in the area where the two beams pass through each other. A target that is within this center area is tracked and positional information on range, elevation, and azimuth is updated each time the beams sweep through the area.
The phased array radar is a product of the application of computer and digital technologies to the field of radar design. A phased array is a complex arrangement of many individual transmitting and receiving elements in a particular pattern. Common arrays include linear, planar, curved, and conformal, with linear being the most common. By using a computer to rapidly and independently control groups of these individual elements, a phased array antenna can, in effect, radiate more than one beam from the antenna. Multiple beams and computer processing of radar returns give the phased array radar the ability to perform the TWS function. The most common employment of the TWS capability of the phased array radar is in the air-to-air arena.
The number of individual transmitting and receiving elements is limited by the size of the radar antenna. The number of targets phased array radar can track is limited by the number of independent beams the antenna can generate. Many phased array radars, especially air-to-air radars, do not track and scan simultaneously, but rapidly switch between the two modes to overcome this limitation.
Modern TWS radars employ computer signal processing and complex computer algorithms to simplify the problem of target correlation. Air-to-air radar typically uses a raster scan to search a volume of airspace. In the search mode, the radar simply presents all targets detected in this airspace to the pilot on his radar display. In the TWS mode, the radar employs computer processing to figure out target correlation and update target information. This is done automatically, and the results are presented on the display.
In radar technology and similar fields, track-before-detect (TBD) is a concept according to which a signal is tracked before declaring it a target. In this approach, the sensor data about a tentative target are integrated over time and may yield detection in cases when signals from any particular time instance are too weak against clutter (low signal-to-noise ratio) to register a detected target.
The TBD approach may be applied both for pure detection when the tentative target displays a very small amount of apparent motion, as well as for actual motion tracking. In the first case the problem is considerably simpler, both in terms of the amount of calculation and the complexity of algorithms
The function of the antenna during transmission is to concentrate the radar energy from the transmitter into a shaped beam that points in the desired direction. During reception, or listening time, the function of the antenna is to collect the returning radar energy, contained in the echo signals, and deliver these signals to the receiver. Radar antennas are characterized by directive beams that are usually scanned in a recognizable pattern. The primary antenna types in use today fall into three categories: parabolic, Cassegrain, or phased array antennas. Additionally, the method radar antennas employ to sample the environment is a critical design feature of the radar system. The scan type selected for a particular radar system often decides the employment of that radar in an integrated air defense system (lADS). The process the radar antenna uses to search airspace for targets is called scanning or sweeping.
One of the most widely used radar antennas is the parabolic reflector.
The parabola-shaped antenna is illuminated by a source of radar energy, from the transmitter, called the feed. The feed is placed at the focus of the parabola, and the radar energy is directed at the reflector surface. Because a point source of energy, located at the focus, is converted into a wavefront of uniform phase, the parabola is well suited for radar antenna applications. By changing the size and shape of the parabolic reflecting surface, a variety of radar beam shapes can be transmitted.
The antenna depicted in Figure generates a nearly symmetrical pencil beam that can be used for target tracking.
Elongating the horizontal dimensions of the parabolic antenna creates a radar antenna called the parabolic cylinder antenna. The pattern of this antenna is a vertical fan-shaped beam. Combining this antenna pattern with a circular scan technique creates a radar system well suited for long-range search and target acquisition.
Elongating the vertical dimensions of the parabola creates a radar antenna that generates a horizontal fan-shaped beam with a small vertical dimension. This type of antenna is generally used in height-finding radar systems.
Another variation of the basic parabolic antenna includes using an array of multiple feeds instead of a single feed. This type of parabolic antenna can produce multiple radar beams, either symmetrical or asymmetrical, depending on the angle and spacing of the individual feeds.
A Cassegrain antenna uses a two-reflector system to generate and focus a radar. The primary reflector uses a parabolic contour, and the secondary reflector, or subreflector, has a hyperbolic contour. The antenna feed is located at one of the two foci of the hyperbola. Radar energy from the transmitter is reflected from the subreflector to the primary reflector to focus the radar beam. Radar energy returning from a target is collected by the primary reflector and reflected as a convergent beam to the subreflector. The radar energy is rereflected by the subreflector, converging at the position of the antenna feed. The larger the subreflector, the closer it can be to the primary reflector. This reduces the axial dimensions of the radar but increases aperture blockage due to the subreflector. A small subreflector reduces aperture blockage, but it must be positioned at a greater distance from the primary reflector.
To reduce the aperture blockage by the subreflector and to provide a method to rapidly scan the radar beam, the flat plate Cassegrain antenna was developed.
The fixed parabolic reflector is made up of parallel wires spaced less than a half wavelength apart and supported by a low-loss dielectric material. This makes the fixed parabolic reflector polarization sensitive. It will completely reflect one type of linear polarization and be transparent to the orthogonal polarization. The fixed antenna feed, in the middle of the moveable mirror, transmits a radar signal polarized to be reflected by the parabolic reflector. The moveable mirror is constructed as a twist reflector that changes the polarization of the radar signal by 90°. The signal from the feed is reflected by the parabolic reflector to the mirror, which rotates the polarization 90°. This rotation makes the transmitted signal transparent to the parabolic reflector, and the signal passes through with minimal attenuation. The radar beam can be scanned over a wide area by rotating the moveable mirror. A deflection of the mirror by the angle Ɵ results in the beam scanning through an angle of 2Ɵ.
The geometry of the Cassegrain antenna is especially well suited for monopulse tracking radar applications. Unlike the parabolic antenna, the complex feed assembly required for a monopulse radar can be placed behind the reflector to avoid aperture blocking.
PHASED ARRAY ANTENNA
The phased array radar is a product of the application of computer and digital technologies to the field of radar design. A phased array antenna is a complex arrangement of many individual transmitting and receiving elements in a particular pattern. A phased array antenna can, in effect, radiate more than one beam from the antenna by using a computer to rapidly and independently control groups of these individual elements. Multiple beams and computer processing of radar returns give the phased array radar the ability to track-while-scanning and engage multiple targets simultaneously.
Phased array radar uses the principle of radar phase to control the individual transmitting and receiving elements. When two transmitted frequencies are in-phase, their amplitudes add together, and the radiated energy is doubled.
When two transmitted frequencies are out-of-phase, they cancel each other.
Phased array radars use this principle to control the shape of the transmitted radar beam.
Phase relationships and antenna element spacing determine the orientation of the transmitted beam. For eg, antenna elements A and B are separated by one-half wavelength and are radiating in-phase, that is, when one is at the positive peak, the other is also at a positive peak. Since the elements are one-half wavelength apart, when the positive peak radiated by A reaches B, B will be radiating a negative peak. As the peaks propagate along the X axis, they will cancel each other out. The total radiated power along that axis will be zero. Along the Y axis, however, the positive peaks from A will add to the positive peaks from B, causing the total radiation along this axis to be at its maximum value. This type of array is called a “broadside array” because most of the radiation is in the direction that is broadside to the line of the antenna array.
The computer controlling the phase of the signal delivered to each transmitting and receiving element of a phased array antenna controls the direction and shape of the radiated beam. By shifting the phase of the signals between 0° and 180°, the beam sweeps. This is the basic means of producing an antenna scan. In addition, the amplitude, or power, of the signal applied to each element can be varied to control the sidelobes. This alters the shape of the beam which affects the range capability and angular resolution of the radar.
Depicts a variation of the phased array antenna, known as a planar array antenna. A planar array antenna uses transmit and receive elements in a linear array, but, unlike the phased array radar, the elements are smaller and are placed on a movable flat plate. The ability to simultaneously track several targets is one advantage of this type of radar.
The most important characteristic of any type of antenna is antenna gain.
Antenna gain is a measure of the ability of an antenna to concentrate energy in the desired direction. Antenna gain should not be confused with receiver gain, which is designed to control the sensitivity of the receiver section of a radar system. There are two types of antenna gain: directive and power.
The directive gain of a transmitting antenna is the measure of signal intensity radiated in a particular direction. Directive gain is dependent on the shape of the radiation pattern of a specific radar antenna. The directive gain does not take into account the dissipative losses of the antenna. Directive gain is computed using Equation
GD = Maximum radiation intensity / Average radiation intensity
The power gain does include the antenna dissipative losses and is computed using Equation
Power gain = max radiation intensity/ Radiation intensity of an isotropic antenna
The term isotropic antenna describes a theoretical spherical antenna that radiates with equal intensity in all directions. This results in a spherical radiation pattern. The power density for any point on an isotropic antenna is the radiation intensity and can be calculated by dividing the total power transmitted (PT) by the total surface area of the sphere,
Power density (Isotropic Antenna) = PT (watts)/ 4*Pie*r2 (Cm2)
The radiation pattern of an isotropic, or spherical, antenna would provide neither azimuth nor elevation resolution and would be unusable for radar applications. To provide azimuth and elevation resolution, a practical antenna must focus the radar energy. The power density of a practical antenna differs from the isotropic antenna only in terms of antenna gain (G).
Power Density (Practical antenna) = PT*G/ 4*pie*r2
The actual power gain (G) of a practical antenna can be calculated by using Equation
Ae= effective area of aperture
Lamda = Wavelength of the radar
The power density and gain of an antenna are a function of the antenna pattern of a radar system. Figures illustrate the antenna pattern of a typical parabolic antenna. Most of the power density of the radar is concentrated in the main beam. However, since the radar is not a perfect reflector, some radar energy is transmitted in the sidelobes. In addition, there is spillover radiation due to the energy radiated by the feed that is not intercepted by the reflector. Finally, the radar has a back lobe caused by diffraction effects of the reflector and direct signal leakage. Sidelobes and backlobes are all undesirable radiations that adversely affect the maximum radar range and increase the vulnerability of the radar to certain jamming techniques.
The recent article appeared in India Today, based on a decade old report triggered a series of debates about the capabilities of Tejas aircraft. So we decided to create an article comparing one of the world’s most dominant single engine fighter that is Gripen NG with Tejas.
The Gripen has American Engine, IRST and AESA radar made by an Italian-British company, missile launch rails made by an American company, Cockpit made by an Israeli company, many other foreign components and foreign weapons. Still the Gripen is called an Indegeneous Weapon nobody has any problem in buying Gripen. Because it is Gripen It is not HAL Tejas. In HAL Tejas apart from engine and Radar there is rarely anything that has been a foreign product. Still people say Tejas not indigenous.
Saab has been making aircrafts since the 1930s. They take 70 years to produce an aircraft like Gripen NG, we only take 30 years to develop an aircraft like Tejas. There is lot of problems faced from the start of the project and the western sanctions also affect the program still we managed to develop a world class fighter. 65% of Tejas is ingenuously developed. Tejas MK 2 will incorporate 90% indigenous tech and surely it can outperform Gripen NG in many areas. Gripen considered as one of the best multi role fighter in the world. Many defense analysts place Gripen inside the top 10 table. We must be proud of by our achievements and must support our great scientists.
The comparison between Tejas and Gripen is in the following 4 criteria’s
Both Tejas and Gripen incorporate a certain amount of stealth. Gripen uses 30% composites & Tejas uses 45 % composites. 90% of the surface of Tejas is made of composites. The RCS of Tejas not publically available. Tejas MK2 will contain 70% of composites surely MK2 will have a considerable advantage in stealth. Both Gripen and Tejas using Radar Absorbent materials and coating for reducing RCS.
RCS of Tejas = 0.5 m2
RCS of Gripen = 0.9 m2
So far as aerodynamics is concern, Gripen is an excellently designed plane which gives it a very good speed and long range. LCA Mk1 was considered to be a bit draggy but a lots of studies have been made to improve its aerodynamics is concern. Making LCA Mk2 1m longer is a part of Aerodynamic improvement process for better compliance of Area rule. There are some other aerodynamics changes which are coming in LCA Mk2. Study says that it will reduce drag by 8% and improve trans sonic acceleration by 20%.. So these aerodynamic changes should make LCA Mk2 a plane with very good aerodynamic characteristic.
For good turning performance wing loading should be low and thrust to weight ratio (TWR) should be high. Tejas has an advantage in both TWR and wing loading. The thrust-to-weight ratio of a combat aircraft is a good indicator of the maneuverability of the aircraft. So Tejas should have better turn rates than Gripen .Tejas shall be at a big advantage because of its light empty weight and should maneuver fast and probably can beat Gripen in close combat. Its small airframe makes it difficult for the enemy pilot to spot in a close combat. Tejas have an advantage of low wing loading also which should give it an edge at high altitude fighting. Some websites claims Gripen has superior Sustained turn Rate than any other aircraft anyway we are not considering it as a credible source. However airplane design always a compromise & both wing loading & TWR can be “adjusted” within some margins to enhance turning performance. We don’t know anything more about the specifications of Gripen to evaluate its maneuverability. Even though Tejas has better turn rates we consider both Tejas and Gripen almost equally maneuverable.
TWR Tejas = 1.07
TWR Gripen = 0.97
Wing loading Tejas = 247kg/m2
Wing loading Tejas = 283kg/m2
Gripen got very good radar, a gallium Nitride based radar. LCA Mk2 is also all set to get top of the class AESA radar till Uttam is ready with 150 KM range. Israel has offered ELTA 2052. Recently Thales has flight-tested active array radar built specifically for Tejas. The radar is based on the company’s successful RBE2 radar installed on Rafale fighter jets. With the latest Thales AESA radar MK1A can kick out any of its adversaries. But still lags behind Gripens GaN Raven radar.
Gripen also going to get a world class IRST in the form of Selex skyward G and tejas doesn’t have any IRST till now. With the help of GaN radar and skyward G IRST gripen can detect stealthy fifth generation fighter aircraft's at long distances.
In Electronic Warfare Gripen is the first aircraft which uses electronic warfare system based on gallium nitride technology, India and Israel are making EW for Tejas and has designed MAYAVI Ew suite for Tejas and work is on for better EW. India has got spectra configured for Indian requirement. If spectra technologies goes in LCA MK2 by the way of buy back clause, it will be superior to Gripen. If not, Indo-Israeli EW will catch up with that of gripen .
So far sensor fusion is concern; Gripen is a top class plane. India is also working on sensor fusion but how much effective that will be is not known. Here is an area where I see gripen is significantly out performing Tejas in current scenario. Gripens sensor fusion is only inferior to F35 , and nobody knows how good will be India’s own sensor fusion. In avionics Gripen is atleast a generation ahead than Tejas Mk1A. May be MK2 can catch up with Gripen NG.
Both Tejas & Gripen have very good targeting pod and weapons . India shall use Python, derby and Russian missiles along with Astra. Gripen uses AIM Series and Meteor missile. Meteor is a top class missile but new Israel claims I Derby can provide 80% of meteor performance. Astra 2 the desi meteor is under development can also be include in Tejas Mk2 weaponry. Both planes are neck to neck in A to A missiles but If Meteor is used, Gripen will have a superior edge. Both will have gun according to their requirement and both can use guided bombs. India has just tested SAAW bomb which will give LCA MK2 an edge in anti airfield strike capability.
Engine and Power
Both Tejas and Gripen deriving the power from same engine GE 414 with a Dry thrust of 62 KN and 98 KN in afterburner. However India is also working on indigenous kaveri engine with the help of Snecma France. New Kaveri engine is supposed to have same power as GE 414. LCA Mk1A has 13.2 M long which is 2 meter short in length of Gripen. Both planes have same g limits. LCA mk1As service ceiling is 16000 m which is higher than the 15240m of Gripen . This is because of low wing loading and will give protection to LCA against many short range and shoulder fire missiles and SAMs. MK2 may have even better service ceiling which will increase the advantage of MK2 over Gripen NG.
Gripen has better speed than Tejas which does not make a big difference. But the super cruising ability of Gripen gives it an advantage of Tejas Mk1A, but we can incorporate super cruise ability in Tejas MK2. However, supercruising uses more fuel to travel the same distance than at subsonic speeds but uses less fuel than afterburner.
Gripens Higher cruise speed allows pilot to surprise the enemy by approaching him from the rear, zone of poorest detection, and to avoid getting surprised by a slower-cruising opponent. It also allows the fighter to choose a time and place of engagement.
In the beyond visual range combat, super cruise capability increases range of the missile shot, and reduces the effective range of adversary’s missiles. If pilot decides to pursue a merge or a visual-range attack pass, its excess kinetic energy again allows it to dictate terms of the engagement. It can also offset a possible situational awareness disadvantage – knowing where the enemy is is of little use if you can’t engage him.
Super cruise is an area where MK1A lag behind Gripen.
Max Speed Of Tejas – mach 1.8
Max Speed Of Gripen – mach 2
LCA MK1A has 500 m take off distance (some sources says it is 700m). Gripen NG has a short take off distance of 400m which favors Gripen and it will reduce at least 15% in Mk2 so mk2 will have equal short take off distance.[Figures may not be accurate ].
Speed at sea level is also against Tejas compared to Gripen, Gripen got 1400 Km/H at sea level Tejas got 1300 Km/H. We believe things will change in Tejas Mk2 with better aerodynamic features Mk2 can catch up with Gripen .
The maximum takeoff weight (MTOW) of an aircraft is the maximum weight at which the pilot is allowed to attempt to take off, due to structural or other limits. MTOW is the heaviest weight at which the aircraft has been shown to meet all the airworthiness requirements applicable to it. Gripen has a MTOW of 16500 Kg Ideally it should be 2.5 times the dry thrust which comes around 15.62 tons but let us assume that it is 16.5 tons as stated in specification. LCA Mk2 uses the same engine so it should have an ability of 16.5 tons MTOW but let us apply that 2.5 factor rule. LCA Mk2 should carry atleast 15.62 MTOW. Now Gripen with 8 ton weight +3.4 ton fuel is left with 5.1 ton payload on plane. On the other hand LCA MK2 with 6.2 ton empty weight and similar fuel of 3.4 ton should left Tejas with 5.7 ton weight which compares favorably to Gripen.
Fuel fraction or propellant fraction, is the weight of the fuel or propellant divided by the gross take-off weight of the craft (including propellant). Fuel fraction of Tejas & gripen is almost similar. So far as range is concern, Tejas should have higher range as both planes are using same engine but Tejas being significantly lighter should have a longer range. But gripen has a considerable advantage in range. An aircraft with more and heavier load (Gripen) should have a smaller radius of action than the same one with less and lighter load (Tejas), due to higher fuel consumption at heavier weights.
Combat Radius of Tejas = 400 Km
Combat Radius of Gripen = 800Km
Why Tejas has less combat radius than Gripen even though both uses similar engines, this is a mystery.
Possible Reasons of Less Combat radius
Both planes are very good having their edge over others in different area. However, Tejas with its small size and very high T/W ratio offers many advantages as a platform. Gripen has significant advantage over Tejas in Avionics and sensor fusion and have slight advantage in weapons its almost similar in all other criteria’s. Tejas MK2 with better Radar, Smart Skin, and Internal Unified Electronic Warfare (Under development) can catch up with Gripen NG. Overall Gripen is the only 4th generation single engine aircraft which has a significant advantage over Tejas.
Why IAF looking for another single Engine Fighter
The major reason behind this is HAL said Tejas MK2 will not come before 2024; HALs engineers and scientists are busy with AMCA project. IAF can’t wait for another 7 or more years for Mk2.And the future technologies expecting in Tejas MK2 will not be a proven one and IAF don’t know how good it will be, it’s a logical choice to go for a proven technology rather than puzzling with indigenous solution and getting hands into theses advanced western techs will positively added up with AMCA ,one more thing is both Tejas and Gripen will come into Air force in the same time, if we avoid foreign single engine fighters we only get 8 -10 Tejas in a year otherwise IAF will get 8-10 tejas plus 8-10 gripen in a year that is significantly adding more number of jets in IAFs fleet, that what exactly IAF want now to deal with the dwindling squadron numbers. IAF interested in Gripen mainly because of the advanced Avionics, sensor fusion, net centric capabilities and Electronic Warfare.
Note:- This is our own views, it dont have any relation with IAF sources.
LCA Mk2 shall be very cost effective and offer India a platform to integrate its own weapon. It will have a lots of configuration options also. Once it is ready in next 5 years with Indian engine , Indian AESA, it will be a weapon very difficult for any other system to match and will give India an edge over any other rival in air combat. It will easily outclass anything china or Pakistan has. India can mass produce it and offer it to many friendly countries across the world including Vietnam, Indonesia, African countries and even to the countries like Brazil who are interested in Gripen. It will offer everything which Gripen offers. What India need at this stage is to expedite LCA Mk2 program and make it sure that it goes into production in as early as possible.
A rough comparison between J10 & Tejas
The J 10 started off as a Chinese attempt at reverse engineering a Pakistan bought US F-16. However it ended up being a modification of Israel’s Lavi multi role fighter, Lavi program was cancelled in 1987 in Israel due to threatening from US. China purchased the blue print from Israel and developed J 10.
The detail of J 10 is hardly available. From the available data it’s very clear that Tejas is not inferior to J 10. J 10 has advantage in weapon loads; range etc only because it is a bigger aircraft so J10 can carry more weapons.
Both aircrafts are pretty much maneuverable. One noticeable aspect of Tejas is its wing loading 247 Kg/m2 is much lower than the 381 Kg/m2 of J 10, which results in better agility. This low wing loading of Tejas gives better climb of rate & also gives good cruising performance cause it need less thrust to maintain the stable flight. This better climb rate is a give Tejas advantage in Himalayan regions. Heavier loaded wing is efficient in higher speed because it causes less drag but in overall performance level low wing loading offers better performance. Another advantage is a fighter with low wing loading can maintain better sustained turn rate (maximum turn an aircraft can achieve) aircraft with higher wing loading may have better instantaneous turn rate. So it is clear that in Himalayan regions a low wing loading Tejas can outperform a higher wing loading J 10 in most criteria’s.
Another important factor affecting the performance of Chinese J10 is the altitude of China's main airbases "along with the prevalent extreme climatic conditions seriously restrains the performance of aircraft, which reduces the effective payload and combat radius by an average of 50%." In other words, the lower density of air at high-altitude Tibetan bases prevents Chinese Air Force fighters such as the Su-27, J-11 or J-10 from taking off with a full complement of weapons and fuel. These aircraft would, therefore, enter a fight with the IAF at a severe disadvantage in the event of a conflict. The IAF, on the other hand, operates fighters in the Northeast from bases such as Tezpur, Kalaikunda, Chabua and Hasimara which are located near sea level elevations in the plains. This means "the IAF has no such restrictions and will effectively undertake deep penetration and air superiority missions in the Tibetan Autonomous Region."
Thrust to weight ratio of Tejas is 1.07, which is less compared to 1.15 of J 10. But it can be improved using a better power-plant. Overall the maneuverability is almost similar.
Both aircrafts are fitted with AESA radar, the capabilities of J10 B / J10 C is not available. According to some blogs “J10C is equipped with more advanced radar. It has a greater detection range than the J10 radar to simultaneously track 12 targets and against the ability of the six targets which pose the greatest threat” looks almost similar to Tejas AESA radar.
J 10C has better stealth features than J 10B. Chinese media calling it as a semi stealth fighter, but from our own research, it’s not going to be stealthier than Tejas, even though Chinese media claims it has a new technique to achieve stealth, and some of those claimed J10C is a threat to even F22. Whatever it is,their comparison of J 10C with F 22 is laughable.
Overall Tejas can give tough competition to J 10B and is slightly inferior to J10C, Tejas Mk2 with better aerodynamics and more stealth features, can catch up with J10C.
The primary purpose of radar systems is to determine the range, azimuth, elevation, or velocity of a target. The ability of a radar system to determine and resolve these important target parameters depends on the characteristics of the transmitted radar signal. This chapter explains the relationship of radar frequency (RF), pulse repetition frequency (PRF), pulse width (PW), and beam width to target detection and resolution.
A basic pulse radar system consists of four fundamental elements: the transmitter, the receiver, the antenna, and the synchronizer, or master timer.
The transmitter, through the antenna, sends out a pulse of RF energy at a designated frequency. The presence of a target is revealed when the RF energy bounces off the target, returns to the radar antenna, and goes into the receiver. The master timer measures the time between the transmission of a pulse and the arrival of a target echo.
RF energy travels at the speed of light (c) which is 3 x 108 meters per second. Target range can be computed by using the basic radar range determination equation.
Target Range = (measured Time * Speed of light)/2
Another useful measurement is the radar mile, which is the round trip time for an RF wave to travel to and from a target one nautical mile away. In simple terms the time required for a radar pulse to travel a distance of one nauticalmile and then return to the radar receiver. One radar nautical mile is equal to approximately 12.367 μs
Measured time = (Target Range *2)/ c = (1853 meters *2) / 300000000 = 12.367 Micro Seconds.
Radar timing is usually expressed in microseconds. To relate radar timing to distances traveled by radar energy, you should know that radiated energy from a radar set travels at approximately 984 feet per microsecond. With the knowledge that a nautical mile is approximately 6,080 feet, we can figure the approximate time required for radar energy to travel one nautical mile using the following calculation:
A pulse-type radar set transmits a short burst of electromagnetic energy. Target range is determined by measuring elapsed time while the pulse travels to and returns from the target. Because two-way travel is involved, a total time of 12.36 microseconds per nautical mile will elapse between the start of the pulse from the antenna and its return to the antenna from a target.
This 12.36 microsecond time interval is sometimes referred to as a RADAR MILE, RADAR NAUTICAL MILE, or NAUTICAL RADAR MILE
1 Radar Kilometer = 6.66 Micro Sec
The range in kilometers to an object can be found by measuring the elapsed time during a round trip of a radar pulse and dividing this quantity by 6.66. The range in nautical miles to an object can be found by measuring the elapsed time during a round trip of a radar pulse and dividing this quantity by 12.36.
A limitation on radar detection range is the concept of a second time around echo. A second time around echo occurs when a target echo associated with a particular radar pulse arrives at the antenna after another radar pulse has been transmitted. The radar master timer always assumes the target echo is associated with the last pulse transmitted. This makes the target echo ambiguous in range.
Example: - Radar pulse A takes 372 microseconds to travel to the target and return. Using the range determination equation, actual target range is 30 nautical miles (nm). However, before the target echo returns to the antenna, radar pulse B is transmitted. The master timer associates the target echo of pulse A with radar pulse B, and calculates a target range of 10 nm. This ambiguous and false range is displayed to the operator. Modern radars are designed with second time around echo as important functional modes, and engineers have developed ways to resolve the ambiguity.
A critical aspect of range determination is range resolution. Range resolution is the ability of radar to separate two targets that are close together in range and are at approximately the same azimuth. The range resolution capability is determined by pulse width. Pulse width is the time that the radar is transmitting RF energy. Pulse width is measured in microseconds.
A radar pulse in free space occupies a physical distance equal to the pulse width multiplied by the speed of light, which is about 984 feet per microsecond. If two targets are closer together than one-half of this physical distance, the radar cannot resolve the returns in range, and only one target will be displayed.
The range resolution of the radar is usually expressed in feet and can be computed using Equation
Range Resolution = (pulse width *984 ft)/2
It is the minimum separation required between two targets in order for the radar to display them separately on the radar scope.
The beamwidth of a radar system is the horizontal and vertical thickness of the radar beam. Beamwidth depends on antenna design and is normally measured in degrees from the center of the beam to the point at which the power drops off by half. This half-power point is -3 dB in power drop-off. Beamwidth governs the azimuth and elevation accuracy and resolution capability of a radar system in the same way that pulse width governs radar range accuracy and resolution.
In order for a radar system to figure out target azimuth, the antenna must be aligned with a point of reference and pointed at the target during the transmission and reception of several pulses of radar energy. If the antenna is referenced to true North, the azimuth of the target can be measured relative to true North. Azimuth determination is based on the position of the antenna when the target is being illuminated.
To provide accurate azimuth determination over a large area, many types of radar employ a narrow beam and scan the antenna in a predictable pattern. The most common scan pattern is a 360° circular scan at a constant rate. The plan position indicator (PPI) radar scope display is normally associated with this scan pattern. As the radar beam sweeps, a target is detected and displayed. The position of the antenna, when the target is displayed, shows the relative azimuth.
The azimuth accuracy of a radar system is determined by the horizontal beamwidth (HBW). Consider the following Figure, radar system A has a horizontal beamwidth of 10°. As the beam sweeps, the target is illuminated for as long as it is in the beam. This means that the target covers 10° in azimuth on the PPI scope. Radar system B has a beamwidth of 1°. A target displayed on the PPI scope will cover 1° in azimuth. The narrower the horizontal beamwidth, the better the azimuth accuracy.
Azimuth resolution is the ability of radar to display two targets flying at approximately the same range with little angular separation, such as two fighters flying line-abreast tactical formation. The azimuth resolution capability is usually expressed in nautical miles and corresponds to the minimum azimuth separation required between two targets for separate display. Azimuth resolution depends on the horizontal beamwidth of the radar. The radar system in Figure has a horizontal beamwidth of 10°. The two targets are so cIose in azimuth that the return echoes are blended into one return.
The radar system in the next Figure has a horizontal beamwidth of 1°. The radar beam not only hits the targets, but passes between them without causing a return. This allows the radars to display two distinct radar returns. A small
horizontal beamwidth improves azimuth resolution.
Azimuth resolution, in nautical miles, can be computed using Equation
Azimuth resolution = (Horizontal Beam width * Range) 60
Notice that this equation is the “60 to 1 rule” used for navigation. A 1°beamwidth will yield a one-mile-wide cell at 60 nautical miles.
Since a radar beam is three-dimensional, the vertical beamwidth is the primary factor in determining altitude resolution capability. Altitude resolution is the ability of radar to display two targets flying at approximately the same range and azimuth with little altitude separation, such as two fighters flying a vertical stack formation. The altitude resolution capability is usually expressed in feet and corresponds to the minimum altitude separation required between two targets for separate display. The radar system in Figure has a vertical beamwidth of 10°.
The two targets are so close in altitude that the return echoes depicted on the range height indicator (RHI) are blended into one.
The radar system depicted in Figure has a vertical beamwidth of 1°.This small beam not only hits the targets, but passes between them without causing a return. This allows the radar to display two distinct targets.
Altitude/elevation resolution, in thousands of feet, can be computed using
Altitude Resolution = (Vertical beam width * Range)/ 60
Radar resolution cell
A radar's pulse width, horizontal beamwidth, and vertical beamwidth form a three dimensional resolution cell (RC) . A resolution cell is the smallest volume of airspace in which a radar cannot determine the presence of more than one target. The resolution cell of a radar is a measure of how well the radar can resolve targets in range, azimuth, and altitude. The horizontal and vertical dimensions of a resolution cell vary with range. The closer to the radar, the smaller the resolution cell.
The physical dimensions of a radar's resolution cell can be computed. For a radar with a pulse width of 1 microsecond, a horizontal beamwidth of 1°, and a vertical beamwidth of 10°, the formulas for range resolution, azimuth resolution, and altitude resolution can be used to compute the dimensions of the resolution cell.
For example , at a target range of 10 nm, the physical dimensions of the radar's resolution cell are 492 feet in range, by 1000 feet in azimuth, and 10,000 feet in altitude. These figures can be confirmed by using above Equations. Based on these computations, two, or more, aircraft flying a trail formation closer than 492 feet would be displayed as a single target. Two, or more, aircraft flying line abreast closer than 1000 feet would be displayed as a single target. Two, or more, aircraft flying a vertical stack closer than 10,000 feet would be displayed as a single target. This also shows that the shorter the pulse width, the better the range resolution capability of a radar system. The narrower the horizontal beamwidth, the better the azimuth resolution capability. The narrower the vertical beamwidth, the better the altitude resolution capability.
Another type of resolution is velocity resolution. For a Doppler radar aircraft flying within the conventional resolution cell described above can be distinguished as separate targets if they have enough speed differentials.
Pulse Doppler Velocity Determination
To fully understand how a pulse Doppler radar determines target velocity, it is necessary to know more about the pulsed waveform. To generate a pulse modulated wave, a continuous carrier sine wave, like the output from a CW radar, is combined with a rectangular wave, like that of a pulse radar, to produce the pulse modulated waveform.
Mathematically, any waveform other than a sine wave is composed of many different pure sine waves added in the proper amplitude and phase relationships. In a pulsed modulated waveform, the sine waves correspond to the fundamental frequency, which is the PRF, and the sum of all harmonics in the proper amplitude and phase. The frequency of the harmonic is the basic frequency plus or minus a multiple of the PRF.
Below Figure is a plot of the harmonic content of a pulse modulated waveform operating at a carrier frequency of 2800 megahertz (MHz) with a PRF of 1 MHz. Note the loops of frequencies on either side of the carrier frequency.
These are the additions and subtractions of all the frequencies in the rectangular pulse to the carrier frequency. The important thing to remember is that there are many frequencies present, and a pulse Doppler radar must deal with a crowded frequency spectrum. This becomes even more important when one considers the fact that every frequency present will experience a Doppler shift when it is reflected by a moving target. The individual frequencies shown are called spectral lines.
For a pulse Doppler radar to accurately measure velocity, it must compare the frequency change, or Doppler shift, between the carrier frequency and the frequency returning from the target. It is a difficult task for the radar to differentiate between the returning carrier and all the harmonic frequencies.
The radar differentiates between the returning carrier frequencies and all other harmonic frequencies by using clutter cancellers, or filters, at the known harmonic frequencies. The radar cannot process frequencies cancelled by these filters. The filters create “blind speeds” for the radar. The closer together the spectral lines, the more “blind speeds” the radar will have.
Since the position of the harmonics in relation to the carrier frequency is based on PRF, the number of blind speeds can be reduced by changing the PRF of the radar. The higher the PRF, the wider the spacing of the spectral lines and the fewer blind speeds due to selective clutter canceling. However, a high PRF increases the problem of range ambiguities. Most modern pulse Doppler radars employ a medium and high PRF mode. Medium PRF equates to fewer range ambiguities but more blind speeds. High PRF has fewer blind speeds but more range ambiguities
To separate the returning target frequency shifts from all other frequencies in the returning waveform, the pulse Doppler radar employs filters to cancel the known harmonic frequency shifts. In addition, the radar cancels out all returns with no frequency shift, which equates to canceling all returns with no movement relative to the radar. However, if the radar has too many clutter filters, this creates multiple blind speeds, and targets will be missed.
Basic Radar Equation
The basic radar equation relates the range of a radar system to the characteristics of the transmitter, receiver, antenna, and the target. The radar equation provides a means not only to figure out the maximum range of a particular radar system, but it can be used to understand the factors that affect radar operation. In this section, the simple forms of the radar equation are developed, starting with the power density of the transmitting antenna to the power received by the receiving antenna.
Power density is the power of a radio wave per unit of area normal to the direction of propagation. The power density generated by a practical antenna can be expressed
Power density from Antenna = (PT*G) / (4*pi*r2)
PT = Transmitted Power
G = Antenna Gain
R = Radius of the antenna
As the radar beam propagates through space, it arrives at a target at some range (R) from the antenna. As the radar beam travels through space, the wavefront of the beam expands to a very large cross-sectional area, especially in relation to the target dimensions. The power density of the radar beam, across this wide area, at the target, is detailed in the below Equation
Power Density at Target = (PT*G) / (4*pi*r2)
PT = Transmitted Power
G = Antenna Gain
R = Range to the Target
Since the cross-sectional area of the radar beam is so large, only a small portion of the total power in the beam can be reflected toward the antenna. The rest of the radar energy continues through space and is dissipated, absorbed, or reflected by other targets. The small portion of the radar beam that hits the target is reradiated in various directions. The measure of the amount of incident power intercepted by the target and reradiated back in the direction of the antenna depends on the radar cross section (RCS) of the target. Equation details the power density of the target echo signal reflected back to the radar antenna is below
Power Density at Antenna = [(PT*G) / (4*pi*r2)] * [RCS / (4*pi*r2)]
PT = Transmitted Power
G = Antenna Gain
R = Range to the Target
RCS= Radar Cross Section
As the target echo reaches the antenna, part of the echo is captured by the antenna based on the effective aperture (Ae). Equation details the actual signal power received by the radar system follows. This is one form of the basic radar equation and is the signal strength of a radar return from a specific target at range (R) from the radar.
Signal Power Density(S) = [(PT*G*RCS*Ae) / ((4*pi) 2*r4)]
PT = Transmitted Power
G = Antenna Gain
R = Range to the Target
RCS= Radar Cross Section
Ae = Effective aperture
A detailed analysis of this equation is not required to draw some basic conclusions about the factors affecting the detection of an aircraft. If any factor in the numerator, such as transmitted power, is increased by a factor of three, the signal received by the radar will increase by only 30 percent. This clearly shows why radar system operation is characterized by the transmission of megawatts of power and the reception of microwatts of returning power. In addition, this equation shows that the most critical factor in determining radar detection is target range.
The maximum radar range (RMAX) occurs when the signal power density received just equals the minimum detectable signal (SMIN) for the receiver. Solving Equation for range, and substituting SMIN, yields the basic radar equation for RMAX for a specific target. This is another form of the basic radar equation.
R max = [(PT*G*RCS*Ae) ¼] / ((4*pi) 2* S min)]
PT = Transmitted Power
G = Antenna Gain
R = Range to the Target
RCS= Radar Cross Section
Ae = Effective aperture
Every warhead must have a fuze. Fuzes are the devices which sense the right moment to detonate the warhead. There are numerous kinds of fuzes which operate on different principles and are suitable for different kinds of missiles, warhead and environment of operation. The most common types of fuzes are impact fuze, altitude fuze, and proximity fuze.
Impact fuzes are used in all anti-tank missiles. Some anti-aircraft and anti-ship missiles also are provided with this fuze in addition to proximity fuze. In impact fuze, an electric pulse develops when it hits another solid object with a certain relative velocity which leads to high deceleration or inertia force. This electric pulse is used to trigger the warhead. The values of impact energy required for this purpose are always much above any impact that the missiles may be subjected to during normal handling and transportation operations.
In this type the warhead detonation is initiated on sensing a preset altitude. This altitude sensing could be based on barometric pressure measurement or radio-altimeter reading.
These are most often used when the impact possibility is less due to unavoidable errors in guidance and control, the missile is expected to pass in proximity if the target above or below, left or right within a certain distance. The proximity fuze can be active or passive system. In the active fuze a very low power and low range radar system transmits radiation only when the target is a small distance away and then when it receives certain strength of reflected signal it detonates. It can also be an active laser radar system. In a passive system it is generally infrared based proximity fuze.
Launchers and Ground Support Systems
All the missiles need certain ground systems to help launch them at the specific targets. Launchers are the most important of these systems. The large ballistic missiles are launched from silos under the ground or submarines or moblile vehicle based launchers. The small missiles are launched from a launch-cum-container tube resting on a human shoulder. The launchers can be very demanding piece of engineering effort with precision in aiming the launcher at a particular target and very high rates of turning in elevation and azimuth in case of' antiaircraft missiles.
In addition, the ground support requires target search and tracking facilities which are normally provided by radar or optical sights, television or infrared detectors. If the missile range is say 50 km, the search radar will have range capabilities of as much as 100 km in good weather to give adequate time for launching the missile and intercepting the target at full range of missile. The ground system is developed to withstand the environment.
For certain surface-to-air homing missiles the ground system will also help illuminate the target for the missile to home-in while command generation and transmission system is needed in command guided missiles.
In addition to these we need communication and intelligence systems also on the ground to coordinate the functions of various missile launching units and have adequate information on targets. We also need to identify between enemy aircraft and friendly aircraft before launching a missile. This system is called IFF (Identification Friend or Foe). In this audio signal at known frequencies is beamed at the suspected target and if the signal is returned by the aircraft (it is automatic without pilot's participation) then it is friendly. In the case of long distance missiles extensive support in the form of ground computers and power supplies and air-conditioning, etc., are needed.
Check out and Simulators
To certify the missiles worthy of deployment and ready for operation, a periodic health monitoring of
its vital subsystems is carried out. This is generally done through an automatic and computerized check procedure on the ground. Similarly, simulators are provided specifically for training the personnel in the operation of the missile. These simulate all the functions of the missile's electrical and microwave components.
Extensive testing of missiles proceeds with their deployment. This testing is in two phases, i.e. development testing and user evaluation testing. These tests are done at test ranges which are suitably located keeping in view the safety requirements. The ranges have instrumentation facilities to collect data for evaluation of the missile flight. The safety zones of these regions a.re very much dependent upon the size and range of the missile and the flight path. Some of the ranges are located close to the sea while some others are located in the desert areas. In India the major range facility is located in Orissa at Balasore. There are two other test ranges equipped with instrumentation for testing launch vehicles, Thumba near Trivandrum and Sriharikota. These ranges are mainly for the use of Space Department. The instrumentation facilities provide for tracking radars, electro-optic instruments and telemetry receiving stations and meteorological facilities. In the range, flight tests are carried out from the Block House. Real-time data processing facilities and other facilities exist to ensure the range safety for carrying oat flight vehicles in case of using telemetry command system.
This is the last article of our article series - Missile Technology
Thanks for reading ................
10) Mountain strike corps (XVII Corps)
XVII Corps of Indian army is the first mountain strike corps of India which has been built as an quick reaction force and as well as counter offensive force against China along LAC . Its headquarters are located at Panagarh in West Bengal.
India needs at least two Strike Corps to take the war into Chinese territory - one each for Ladakh and Arunachal Pradesh. On July 17, 2013, the Cabinet Committee on Security (CCS) approved the Army’s proposal for raising a Strike Corps for the mountains. Though the approval came after considerable delay, it was a pragmatic move that would send an appropriate message across the Himalayas.
It will help India to upgrade its military strategy against China from dissuasion to meaningful deterrence as the Strike Corps, in conjunction with the Indian Air Force (IAF), will provide the capability to launch offensive operations across the Himalayas so as to take the next war into Chinese territory, while simultaneously defending Indian territory against Chinese aggression. It would break through Chinese defences, cross over into the Tibetan plateau and capture territory that would be a bargaining chip in a post-conflict settlement. Mountain Strike Corps will have strength of around 90,000 soldiers. The army was told to complete the raising of the mountain strike corps by financial year 2017-18.
India achieved significant advancements in the direction of developing a two-layered Ballistic Missile Defence system. This enhances India's capability of dealing with a nuclear attack threat. Introduced in light of the ballistic missile threat from mainly Pakistan, it is a double-tiered system consisting of two land and sea-based interceptor missiles, namely the Prithvi Air Defence (PAD) missile for high altitude interception, and the Advanced Air Defence (AAD) Missile for lower altitude interception. The two-tiered shield should be able to intercept any incoming missile launched from 5,000 kilometres away. The system also includes an overlapping network of early warning and tracking radars, as well as command and control posts.
Development of the anti-ballistic missile system began in 1999. Around 40 public and private companies were involved in the development of the systems. Defence Research and Development Laboratory (DRDL) developed the mission control software for the AAD missile. Research Centre, Imarat (RCI) developed navigation, electromechanical actuation systems and the active radar seeker. Advanced System Laboratory (ASL) provided the motors, jet vanes and structures for the AAD and PAD. High Energy Materials Research Laboratory (HEMRL) supplied the propellants for the missile.
Two new anti ballistic missiles that can intercept IRBMs are being developed as part of Phase 2. These high speed missiles (AD-1 and AD-2) are being developed to intercept ballistic missiles with a range of around 5,000 km. The test trials of these two systems are expected to take place in 2011. The new missile will be similar to the Terminal High Altitude Area Defense missile deployed by the US. These missiles will travel at hypersonic speeds and will require radars with scan capability of over 1,500 km (930 mi) to successfully intercept the target. India is also planning to develop a laser based weapon system as part of its defence to intercept and destroy missiles soon after they are launched towards the country. DRDO's Air Defence Programme Director V K Saraswat says its ideal to destroy a ballistic missile carrying nuclear or conventional warheads in its boost phase. Saraswat further added that it will take another 10–15 years for the premier defence research institute to make it usable on the ground.
Defence Research and Development Organisation (DRDO) is working on India's future main battle tank (FMBT) with a 1,500-horsepower (HP) indigenous engine. This tank will replace beyond 2020 the imported T-72 tanks, renamed Ajeya, with the Army. Various specifications for the FMBT have been finalised. The country's military, which has projected a need for about 1,200 FMBTs. For engine development, formed a national team comprising members from the academia, the user, industry and the DRDO.
The FMBT will weigh only 50 tonnes compared to Arjun-Mark II's 62 tonnes. The DRDO is simultaneously working on Arjun-Mark II. The volume occupied by the electronics package in the FMBT will be less. The FMBT's engine will be two-thirds the size of Arjun-Mark I's, but will generate 1,500 HP compared to Arjun-Mark I's 1,400 HP. Improvements in material, fuel injection and filtration technologies will contribute to the reduction in the engine size without compromising on power.
Combat Vehicles Research and Development Establishment (CVRDE) are in the process of developing the FMBT with latest technologies. It is working in following areas:
7) Vishakapattanam class and NGD
Visakhapatnam class (Project 15B) is a class of stealth guided missile destroyers currently being built for the Indian Navy. Based on the Kolkata-class design, the Visakhapatnam class will be an extensively improved version. Ordered in 2011, the first ship is expected to be completed in 2018. Project 15B destroyers will feature enhanced stealth characteristics as well as incorporate state of the art weaponry and sensors.
The first ship of Project—15B guided missile destroyer, christened Visakhapatnam. was launched on 20 April 2015 at a ceremony at Mazagaon Dock Limited (MDL), Mumbai. The Visakhapatnam is the first of four destroyers of the class designed by the Directorate of Naval Design in New Delhi. The stealth warship has a displacement of 7,300 tons and is 163 meters long. These ships will be propelled by four gas turbines in Combined Gas and Gas (COGAG) configuration and are capable of achieving speeds in excess of 30 knots [the warships can achieve a maximum speed of 31-32 knots] with a maximum endurance of 4000 nm. The Visakhapatnam-class vessels are designed to carry two multiple-role helicopters and are equipped with a vertical launching missile system capable of engaging shore- and sea-based targets from long range.
The P15B destroyers incorporate new design concepts for improved survivability, sea keeping, stealth and ship maneuverability. State of art rail less helo traversing system is being introduced on these ships for efficient helicopter handling onboard. By increasing the cavitation inception speed the hydrodynamic noises and vibrations have been effectively reduced at the cruising speed in each of the ships of Project 15B.
These ships can truly be classified as possessing a Network of Networks, as they are equipped with Integrated Platform Management System (IPMS), Ship Data Network (SDN), Automatic Power Management System (APMS) and Combat Management System (CMS). While control and monitoring of machinery and auxiliaries is achieved through the IPMS, power management is done using the APMS. The CMS performs threat evaluation and resource allocation based on the tactical picture compiled and ammunition available onboard. The SDN is the information highway on which data from all the sensors and weapons ride.
Stealth has been a major thrust area in P15B design. Enhanced stealth features have been achieved through shaping of hull and use of radar transparent deck fittings which make these ships difficult to detect. The ship embodies features such as Multiple Fire Zones, Total Atmospheric Control System (TACS) for Air Conditioning, Battle Damage Control Systems (BDCS), Distributional Power Systems and Emergency DA to enhance survivability and reliability in emergent scenarios.
These ships are also packed with an array of state of the art weapons and sensors, including vertically launched missile system for long distance engagement of shore and sea-based targets. The ship is one of the few warships of the world to be fitted with a Multi Function Surveillance Threat Alert Radar to provide target data to Long Range Surface to Air Missile system. The MF-STAR and LRSAM system is being supplied by M/s BEL. To protect against incoming airborne and surface threats at medium and close range, the ship has 76mm and 30mm gun mounts.
Indian Navy are now planning and conceptualising next generation destroyers which would be new in design and more potent. Next-generation destroyers will have additional features than the Project 15, Project 15 A and Project 15 B. NDG will be of 13000-tonne displacement warship with conventional propulsion and will feature next-generation weapons including laser weapons.
6) HSTDV & Brahmos2
HSTDV is an unmanned scramjet demonstration aircraft for hypersonic speed flight. The HSTDV program is run by the Indian Defence Research and Development Organisation. The Defense Research and Development Laboratory’s Hypersonic Technology Demonstrator Vehicle (HSTDV) is intended to attain autonomous scramjet flight for 20 sec., using a solid rocket launch booster. The research will also inform India’s interest in reusable launch vehicles. The eventual target is to reach Mach 6.5 at an altitude of 32.5 km. (20 mi.).
India’s Defence Research and Development Organisation developed Hyper-sonic Technology Demonstrator Vehicle (HSTDV) unmanned scram-jet demonstration aircraft for hypersonic speed flight is all set for developmental flight by end of this year. Integration of all final flight hardware is happening right now and the team and is confident to conduct first hydrocarbon flight with scram-jet combustor by late this year thus joining an Elite group of countries in the world who have initiated their own scramjet engine research for hypersonic flight above Mach 5.
HSTDV Cruise vehicle will be mounted on a solid rocket motor which is covered by fairings will take it to the required altitude and once required altitude and Mach numbers are achieved cruise vehicles will be ejected out of the launch vehicle and later Scramjet engine will be auto-ignited mid-air thus taking over to propel cruise vehicle for next 20 seconds at Mach 6. The aim of planned flight test of the project is to demonstrate autonomous flight of Hypersonic scramjet integrated vehicle using hydrocarbon fuel and also measure aerodynamics of the air vehicle, its thermal properties and scramjet engine performance. HSTDV will have a flight duration of 20 seconds at an altitude of 31 km which is also cruising altitude of Boeing 747 but at Mach 6. Scramjet combustor under development is of 520kg thrust engine which has cleared 4 static test for the 20-second duration at ground test facilities at simulated speed entry condition of Mach 2.25. Performance evaluation testing of scramjet combustor was carried out on the last leg off ground-based trials last year in June which was declared successful and scramjet combustor engine was cleared for the first flight.
A supersonic missile is bad enough. But a hypersonic missile with a scramjet engine (where the through passing air is combusted at supersonic speeds unlike in ramjet engines where the air is slowed down to subsonic speeds before combustion) at Mach 20 plus is so indefensible you might as well give up the ghost. And its has tremendous range extension utility. For instance an Agni-5 with a hypersonic last stage will extend its range well beyond intercontinental distances. The Indian HSTDV-2 with a platypus nose, a titanium underside and aluminum-niodium topside, could be a strategic killer.
Probably India be only the 3rd country which posses such an advanced weapon. There are rumors that India is backing of from the project because of pressure from certain Western quarters rattled by the prospect of India’s acquiring such a potent weapon. A test of the Hypersonic Technology Demonstrator Vehicle — HSTDV-2, scheduled at TsAGI (Central Thermal Hydrodynamics Institute) in the Moscow metropolitan region in December 2014 was abruptly cancelled. The rumour is Finance Ministry did not sanction the few crore rupees worth of funds required for trans-shipping the item, testing it in Moscow.
Brahmos 2 is a hypersonic cruise missilecurrently under joint development by Russia's NPO Mashinostroeyenia and India's Defence Research and Development Organisation, which have together formed BrahMos Aerospace Private Limited. It is the second of the BrahMos series of cruise missiles. The BrahMos-II is expected to have a range of 290 kilometres and a speed of Mach 7.There is possibilities of extending the range because India joined MTCR recently.
During the cruise stage of flight the missile will be propelled by a scramjet airbreathing jet engine. Other details, including production cost and physical dimensions of the missile, are yet to be published. It is expected to be ready for testing by 2020. Expert’s belives Brahmos 2 will be based on Russian Zicron Hypersonic Maneuvering Cruise missile. Russia is developing a special and secret fuel formula to enable the BrahMos-II to exceed Mach 5.
5) Agni 6
Agni-VI is an intercontinental ballistic missile being developed by the DRDO for the use of the Indian Armed Forces Strategic Forces Command. Agni-6 ICBM visualises a range of 6,000-7,500 km; a larger payload capability than the Agni-5 to carry multiple independently targetable re-entry vehicles (MIRVs); and even manoeuvrable re-entry vehicles (MARVs) to increase survivability against enemy anti-ballistic missile systems.
The SLBM version of missile will arm the Arihant class submarines of the Indian Navy. DRDO revealed in 2012 that it is also in the process of developing another variant of Agni-VI missile. This will be a submarine-launched solid-fuel missile with a maximum range of 6,000 kilometres and a payload of three tonne
4) INS Vishal
INS Vishal (IAC-II) is the follow-on class of Vikrant aircraft carrier currently in its design phase, which will be built by Cochin Shipyard Limited for the Indian Navy. It is intended to be the first supercarrier to be built in India. The proposed design of the second carrier-class will be a new design, featuring significant changes from INS Vikrant (IAC-I), including an increase in displacement. Vishal will displace 65,000 tonnes. It will be propelled by nuclear energy
Navy already has finalised specifications of the second aircraft carrier which will include nuclear propulsion. Reactor technologies will come from India’s first nuclear submarine INS Arihant. Equipping INS Vishal with nuclear propulsions seems to be to gain greater operational endurance since warship powered by nuclear reactor means energy is unlimited and it can operate for over 20 years without refuelling
The carrier will travel at 30 knots, a hair above the Vikrant, and come in at a length of 300 meters, longer than the 262 meter Vikrant. The Navy’s letter of request also outlines plans for the carrier to field between 30 and 35 fixed-wing combat aircraft and 20 rotary wing aircraft. The Navy’s letter of request states that that carrier will be the first in the Indian fleet—and first non-Western carrier—to field a catapult launched but arrest landing (CATOBAR) aircraft launch system. There is a possibility that the CATOBAR system could incorporate General Dynamics’ new electromagnetic aircraft launch system (EMALS) technology.
Vishal will have integrated electric propulsion (IEP) or integrated full electric propulsion (IFEP) has been finally zeroed in to be integrated. IEP eliminates the mechanical connection between the engines and the propulsion which in turn reduces need for clutches and even Gear Box , Advantage of IEP for Surface ships has many advantages like reduction of weight and volume, Reduction in acoustic signatures, better placement of engines in the hull and reduced manpower for its maintenance .
Indian Navy is looking to buy four carriers-based- airborne early warning and control aircraft for INS Vishal for which Northrop Grumman has provided Navy technical information on its E-2D Advanced Hawkeye which is only AEW platform which can operate from aircraft carriers.
3) Ghatak UCAV
The classified effort to build a stealthy unmanned combat air vehicle formally received sanction as a ‘Lead-in Project’ last May, with the first funds released earlier this year. A project that has direct oversight from the Prime Minister’s Office and the National Security Advisor, Ghatak (which began as the DRDO’s Autonomous Unmanned Research Aircraft – AURA) has remained steadily out of view.
Ghatak will be powered by a modified dry thrust version of the Kaveri engine (read on for more details of this modification), will sport a flying wing planform with internal weapons and will sport stealth characteristics developed wholly in-house. Let’s now get into what hasn’t ever been reported before about the Ghatak/AURA programme.
While the Aeronautical Development Agency (ADA) is overseeing the programme along with the Gas Turbine Research Establishment (GTRE), the real R&D is being frontfooted by two academic institutions: IIT Bombay and IIT Kanpur. Since 2013, low speed experiemental studies have been carried out on the Ghatak’s serpentine intake by a team at IIT Bombay. This team has been made a kind of mini ‘Skunk Works’ towards proving computational fluid dynamics on the Ghatak, with no limits on resources and access to facilities.
Two, two specialised research teams at IIT Kanpur were roped in in 2015 for wind tunnel testing of a low RCS intake (work began in mid-2016). The second was even more significant — in November 2015, a team from IIT Kanpur was brought on board to conduct and study the autonomous flight of a low RCS aircraft configuration with a ducted fan for multiple flight modes. Scientists shared the following image with Livefist, never seen before, that provides the first official schematic of the power/thrust configuration on the Ghatak.
Over the last three-four years, the Aeronautical Development Agency has been made aware by several foreign airframers, including stealth pioneer Lockheed-Martin, Dassault, Boeing, BAE Systems,and even MiG Corp that they’d be willing to assist the Ghatak programme in a possible variety of ways — either as offsets, or a commercial consultancy arrangement. Livefist can however confirm that the Narendra Modi government has decided that the stealth component of the Ghatak programme will be entirely in-house, and will be limited to academic institutions and private industry in country.
Scientists on the AURA/Ghatak programme confirm to Livefist that concept UCAV is tied in several ways to the fifth generation AMCA development , which itself could see technology infusions from a line-up of interested suitors, including Saab, Boeing and Dassault Aviation. The latter is keen to use its Rafale deal offset commitments to feed technologies into the Ghatak (and AMCA) programmes. The ‘Lead-in project’ sanction that the ADA obtained for the government was in fact a joint sanction for both programmes, given the huge number of common R&D elements, including shaping, materials, construction, intake geometry, data-links and avionics, weapons and of course the Kaveri engine. Top sources at ADA say that full project sanction for the modified Kaveri engine.
2) Arihant Class & Next Gen SSN
The Arihant class is a class of nuclear-powered ballistic missile submarines being built for the Indian Navy. They were developed under the US$2.9 billion Advanced Technology Vessel (ATV) project to design and build nuclear-powered submarines. The lead vessel of the class, INS Arihant was launched in 2009 and after extensive sea trials, was confirmed to be commissioned in August 2016.
A follow-on class of 6 SSBNs codenamed S5 is under development. INS Aridhaman is the second Arihant-class submarine. In August 2017, it was reported that she would be launched soon and would undergo outfitting. Harbor trials and sea trials are expected to last for 2 years and commissioning is expected sometime in 2019. Work on the third SSBN submarine is going on simultaneously but details are not available.
Next Gen SSN
Government cleared a project to build six new hunter killer boats (SSN) for the Navy. A joint Navy, BARC and DRDO project, the boats will be designed by Navy’s Directorate of Naval Design and be powered by a new reactor being developed by BARC. SSNs are as important as SSBNs as they can blockade important sea routes, denying the enemy access to important resources in an event of war, and shadow enemy ships. This new SSN will be similar in size to the Arihant-class but will carry advanced torpedoes and be able to move much quicker.
1) AMCA & FGFA
Advanced Medium Combat Aircraft (AMCA) is an Indian programme to develop a 5+ generation fighter aircraft. More than four thousand staff devoted to the project, according to a report in 2015. ADA had settled upon a final design involving a twin-engine, canted twin-tail configuration, with an overall profile similar to that of the American F-22 Raptor. Mock-ups of this design have already reportedly undergone wind-tunnel and radar cross-section tests.
ADA pitches the AMCA as one of the world’s top dogfight dukes, boasting “extended detection range and targeting, supersonic persistence and high speed weapon release”. Close-combat operations will be facilitated by “high angle of attack capability, low infrared signature and all round missile warning system.
Four prototypes are expected in 2019”. That may sound overly optimistic – especially in the backdrop of stealth fighter programmes in the U.S., Russia and South Korea experiencing developmental issues. However, it is also a pointer to the Indian defence establishment’s confidence in its ability to develop an entire weapons platform from scratch after the success of the Tejas Light Combat Aircraft.
According to Livefist the first 1:1 full scale model AMCA is being built in Bengaluru. Later this year, the model will undergo a series of rigorous tests at an RCS facility in Hyderabad, where the programme team will have its fest chance at seeing how the shape they’ve chosen for the jet deals with radiation. The exercise will be historic. Because it will be the first time India will be specifically testing a stealth airframe.
Fifth Generation Fighter Aircraft (FGFA) or Perspective Multi-role Fighter (PMF) is a fifth-generation fighter being developed by India and Russia. It is a derivative project of the Russian Sukhoi Su-57 being developed for the Russian Air Force.
India and Russia inked an inter-governmental pact for the FGFA project in 2007. Proposed development of FGFA based on Su-57 5th Generation fighter aircraft has been under negotiation for last 7 years and recently Indian Air Force submitted a favorable report on co-development of FGFA but it also pushed for far more Transfer of technology and deeper Indian involvement in the project.
IAF is looking for Indian built FGFA to have nearly 70-80 % of components which can be sourced from India with Russian imports limited to less than 20-30 % range. IAF reportedly is also asking for better high thrust engines which have better serviceability and also have higher Indian made components.
Apart from this there is many other ongoing as well as completed projects such as , Project 17 A, Rafale , Tejas MK2 , Pinaka MK2 ,NETRA AWACS & Next Generation AWACS , Rustom 2 , LCH, LUH, Akash SAM, Ka 226, AH 64 Apache , Chinook 47 , Nirbhay , Kalvari Class Submarines , DSAR, Midget Subs , Next Generation Missile Vessels etc etc
Reference and Info sources
A railgun is a device that uses electromagnetic force to launch high velocity projectiles, by means of a sliding armature that is accelerated along a pair of conductive rails. US is the only country which developed a working rail-gun. Countries like India, China and Russia are researching to develop their own rail-guns. Below you can read a research paper published on Defense Science Journal in 1994. Even though it was an old article the basics are pretty much same.
A rail gun using electromagnetic propulsion was developed to launch hypervelocity projectiles. A 240 kJ, low inductance capacitor bank operating at 5 k V powered the rail gun. Launchers and projectiles were designed and developed for this purpose. The currents producing the launch forces are of the order of hundreds of kA. Even very low impedances for the current through the rail gun circuit are substantial sources of energy losses. A simulation code was developed to optimize the performance of the rail gun. Control and instrumentation facilities were set up along with a computer-based data acquisition system for measurement and analysis. The capacity to launch projectiles of 3-3.5 g weight to a velocity of more than 2.00 km/s was demonstrated.
A facility was devel6ped to launch hypervelocity projectiles using electromagnetic energy. The projectiles were launched using a railgui1. The rail gun consists of two parallel rails and a conducting metalic foil placed behind the insulating projectile. When a high current flows through the rails, the foil explodes and forms a plasma armature. The force acting on the armature is given by
Force at time t = 0.50 * Inductance per unit length of launcher * (current through the launcher at time t) 2
The rail gun currents are in the region of Hundreds of kA. This Lorentz force accelerates the projectile
An electromagnetic propulsion system requires a storage device with an energy density comparable to that of chemical explosives. The most expensive and technologically difficult part of the system is the high-energy electric source. The power sources considered for electromagnetic propulsion are well researched
Capacitor Bank and Charging Unit
The capacitor bank was used as a power source owing to its availability and lower cost despite its lower energy density. A low-inductance, 240 kJ capacitor bank was set up to provide the basic power to the railgun. A high-voltage charging unit was used to charge the capacitor bank.
High Current Switches
The capacitor energy is switched into the railgun by high-power ignitrons. When the peak current is reached, additional high-power ignitrons are used to crowbar the capacitors out of the circuit to obtain a dc pulse. This minimises the stress on the capacitors, the launcher and the projectile.
Low-inductance transmission lines were made using sandwiched conducting plates to maximize the energy transfer to the load. The transmission lines are subjected to repulsive forces owing to the passage of current through them. These, forces were 'estimated to provide proper bolting and bracing to avoid deformation of the transmission lines.
LAUNCHER AND PROJECTILE
Launchers and projectiles are subjected to high plasma pressures. High magnetic fields and high temperatures. In the present railgun set-up, the plasma pressures generated varied between 100 and 150 MPa.
A simple, single pulse driven rail gun launcher was developed with a minimum of metal components in proximity to the bore to maximize the inductance of the launcher and to improve the launch efficiency. The launcher has a 12 mm square bore cross-section. The launcher was fabricated with lengths ranging from 1 to 2 m. The following launcher designs were used for the firings:
The launchers with the last two design modifications proved more reliable and durable than the launchers based on the first design.
Thermal energy transfer from the rails leads to ablation and the melting of the bore materials. Such ablation degrades the performance of the railgun by adding parasitic mass to the plasma. The bore materials should have a high melting point and superior erosion and ablation resistance. High rail conductivity necessitated the use of copper rails. Polycarbonate and fiberglass were most suitable as bore materials. Loose bore to projectile tolerances or variation in bore dimensions can result in plasma leakage. Most of the launchers showed marked deterioration after a few shots. The deterioration could be attributed to changes in the bore dimensions due to the rail insulator ablation. Substantial deposits of carbon were observed inside the bore of the gun and needed cleaning.
The projectiles are made of Perspex or polycarbonate cubes of 12 mm length. Perspex projectiles tended to shatter. Polycarbonate projectiles survived the high plasma pressures. The plasma and the solid armature were both used for carrying the high currents. Most firings were carried out using plasma armature. A plasma armature is formed when Al/Cu foil melts/explodes on the passage of high currents. The foil vaporizes by joule heating to produce plasma to drive the armature. A neoprene obturator was placed at the rear of the projectile to seal the bore against plasma leakage around the projectile. As a deviation, a solid metallic projectile acting as an armature was also used to carry the current.
DATA ACQUISITION AND SIMULATION
A computer-based data acquisition system was set up to monitor important parameters that affect the performance of the railgun. Current transformers and Rogowski coils were used to measure the rail currents in the range6 of 100 to 500 kA. Magnetic probes were used to get the position-time profile of the projectile inside the bore of the gun and railgun current distribution. These probes help detect plasma leakage and formation of secondary arc. The velocity outside the bore of the gun was measured using shorting screens. A high-speed camera was set up to measure the velocity of the projectile and establish the integrity of the projectile at the muzzle end. This is a non-contact method and is free from electromagnetic pickups.
A simulation code was developed to predict the performance of the railgun. The performance of the model was evaluated by monitoring different parameters
All measurements were supported by appropriate software developed to analyse the entire performance of the railgun. The current-time data are used to predict the displacement, velocity and acceleration of the projectile and the plasma pressure.
Some typical railgun trial results are given in Table. Projectile velocities greater than 2000 m/s were obtained for trial no’s 1 to 3. The efficiency varied between 4 to 5 per cent with railgun current in excess of 260 kA. Plasma leakage and formation of secondary arcs were responsible for the lower projectile velocities than expected from the computer model for trial no’s 5 to 7. Trial no.7 was done using a solid conducting projectile made of aluminium. An armature was kept behind the projectile with no ablator. The armature vaporized and the plasma escaped ahead of the projectile. This led to a lower system efficiency and projectile velocity. A solid projectile made of Perspex and armatures made of several copper foils were used in trial no.4. The mass of each foil was kept around 100 mg to avoid the melting of the armature owing to the high railgun current.
Our study has shown that projectiles attain hypervelocity’s by using a single small square bore railgun. In the existing railgun facility the efficiency varied between 4 to 5 per cent. Significant improvement in the efficiency of the railgun set-up is one of the key issues that will determine the use of railguns for various weapon applications. Hence we carried out detailed modelling and simulation of the entire railgun system. The results from the simulation were validated with the measurements. Measurements made at high common mode voltages of around 1000s of volts and high electromagnetic noise were exceptionally good, providing reliable and repeatable records. Intact projectile launch and 2-3 m of free flight projectile were studied using high-speed photography when punctures in the shorting screens were observed. Using a high-speed camera the integrity of the projectile was established beyond doubt. A 12 mm cubical polycarbonate projectile weighing about 3 g could defeat a 6 mm aluminium sheet at 2 m from the muzzle end of the gun). The complete railgun system was also placed in a 5 m long vacuum chamber to study the railgun performance. Our studies are as yet inconclusive. Owing to the failure of some odd capacitors in the capacitor bank, repetitive trials could not be carried using the full energy of the bank. The energy extracted from the capacitor bank varied between 120 and 160 kJ. The kinetic energy of the projectiles can be increased substantially by using a higher-energy capacitor bank as a power source
Due to unknown reasons Rail-gun development was not completed at that time. But from this press release of Ministry of Defense, it is clear that DRDO restarted their work in the field of Electromagnetic rail gun along with other futuristic technologies like Supersonic Missile Assisted Release of Torpedo, Stealth Wing Flying Test bed, AESA Based Integrated Sensor Suite, Multi-Agent Robotics System etc
Defense Science Journal, Val 44, No 3, July 1994, pp 257-262
S.G. Tatake, K.J. Daniel, K.R. Rao, A.A. Ghosh, and I.I. Khan
Armament research & Development Establishment Pune-410121
There are five main things a pilot must remain aware of when contemplating aerial engagement, of which, getting sight of your opponent and keeping sight of them are the most important. Other major factors influence a dog fights are, thrust-to-weight ratio, wing loading, and the "corner speed" (the maximum/minimum speed at which the aircraft can attain the best turning performance). Apart from this, variable limitations must also be considered, such as turn radius, turn rate, and the specific energy of the aircraft. The concept of energy awareness during air combat is not new. Wise use and conservation of energy during combat will increase your chances of victory.
Missiles are generally made from aluminium and its alloys, steel, magnesium and titanium. The major concern is the strength-to-weight ratio of the material. Higher this ratio the better. On account of the high temperatures encountered by missiles flying at supersonic speeds and needs for lighter materials, newer materials are coming into usage. Fibre-reinforced plastics (FRP) like the carbon-carbon variety, graphite compounds, molybdenum, beryllium, etc.
Some of the important factors calling for adequate caution during material selection are as follows:
The individual components of a radar determine the capabilities and limitations of a particular radar system. The characteristics of these components also determine the countermeasures that will be effective against a specific radar system. Here we will discuss the components of basic pulse radar, continuous wave (CW) radar, a pulse Doppler radar, and monopulse radar.
PULSE RADAR SYSTEM
The most common type of radar design is the pulse radar system. The name describes a process of transmitting discrete bursts of RF energy at the frequency of the radar system. The time that pulses are transmitted determines the pulse repetition frequency (PRF) of the radar system. A pulse radar system can figure out range and azimuth. Range is determined by the time that it takes a pulse to go to a target and return. Target azimuth is determined by the relative position, or antenna orientation, when the pulse strikes the target.
A major important item in the aerodynamic missile configuration is the wing or the main lifting surface. A great variety of wing planforms or configurations are used. Without going into the detailed analyses for optimisation of the configuration, only the names of a few well-known theories are stated here.
The linearised theory is used in supersoninc flow over wings. This theory is derived from the exact differential equation of steady compressible flow. There are also a few equations of first order and linear equations called 'Ackeret Theory'. The basic assumptions made are: (a) the airfoil is thin, and (b) the flow is two dimensional, to mention a few typical ideal assumptions which one comes across many a time.
A few higher order terms have been derived making use of constants called the 'Busemann constants' owing their name to the man who derived them. This derivation makes use of expansion series which are mainly mathematical.
A straight wing planform is the one which is often used. Two other basic wing planforms used are delta and swept back wings. There are many variations of these basic planforms. Due to the advantages and disadvantages associated with each of the basic planforms used, a thorough study involving their aerodynamic efficiency, structrual weight and cost of manufacturing is often called for.
In the analysis of wings of arbitrary planform it is important to know whether the leading (and trailing) edge is subsonic or supersonic since the pressure distribution is markedly different for each condition. Extensive experimental investigations have been conducted to determine and compare the aerodynamic characteristics (commonly called as chics') of the basic planforms for practical applications. The factors taken into account are Reynold's number, fluid viscosity and such other dimensional properties. Thus, airfoil is the cross section of a wing which gives a minimum drag and a maximum lift.
The pressure over an airfoil is primarily a function of the angle between the free stream air direction and the surface. The airfoil shape or section for supersonic application is noticeably different from those sections used in the subsonic region. In general, sharp nosed symmetrical airfoil sections of the double wedge, modified double-wedge, or biconvex variety result in the most efficient aerodynamic design.
Every radar produces a radio frequency (RF) signal with specific characteristics that differentiate it from all other signals and define its capabilities and limitations. Pulse width (pulse duration), pulse recurrence time (pulse repetition interval), pulse repetition frequency, and power are all radar signal characteristics determined by the radar transmitter. Listening time, rest time, and recovery time are radar receiver characteristics. An understanding of the terms used to describe these characteristics is critical to understanding radar operation.
PULSE WIDTH (PW)
PW, sometimes called pulse duration (PD), is the time that the transmitter is sending out RF energy. PW is measured in microseconds. It has an impact on range resolution capability, that is, how accurately the radar can discriminate between two targets based on range.
The pulse width of the transmitted signal is to ensure that the radar emits sufficient energy to allow that the reflected pulse is detectable by its receiver. The amount of energy that can be delivered to a distant target is the product of two things; the output power of the transmitter, and the duration of the transmission. Therefore, pulse width constrains the maximum detection range of a target.
Weapons-control radar, which requires great precision, should be able to distinguish between targets that are only yards apart. Search radar is usually less precise and only distinguishes between targets that are hundreds of yards or even miles apart. Resolution is usually divided into two categories; range resolution and bearing resolution.
Range resolution is the ability of a radar system to distinguish between two or more targets on the same bearing but at different ranges. The degree of range resolution depends on the width of the transmitted pulse, the types and sizes of targets, and the efficiency of the receiver and indicator. Pulse width is the primary factor in range resolution. A well-designed radar system, with all other factors at maximum efficiency, should be able to distinguish targets separated by one-half the pulse width time.
PULSE RECURRENCE TIME (PRT)
Pulse recurrence time is also known as pulse repetition time. PRT is the time required for a complete transmission cycle. This is the time from the beginning of one pulse of RF energy to the beginning of the next. PRT is measured in microseconds. PRT is the same as pulse repetition interval (PRI), which is used in radar warning receivers and other electronic warfare support (ES) assets to discriminate between radar systems. It also affects maximum radar range.
ELECTRONIC warfare (EW) is the systems approach to the exploitation and control, to the maximum extent possible, of the electromagnetic (EM) spectrum. It is an important capability that can advance desired military, diplomatic, and economic objectives or, conversely, impede undesired ones. The use by an adversary of the EM spectrum for communications, navigation, and radar functions can be challenged by the techniques and technology of EW systems. In a military application, EW provides the means to counter, in all battle phases, hostile actions that involve the EM spectrum—from the beginning when enemy forces are mobilized for an attack, through to the final engagement. EW exploits the EM environment by sensing and analyzing an adversary’s application of the spectrum and imposing appropriate countermeasures (CMs) to hostile spectrum use.
CHARACTERISTICS OF RF RADIATION
In order for a radar system to determine range, azimuth, elevation, or velocity data, it must transmit and receive electromagnetic radiation. This electromagnetic radiation is referred to as radio frequency (RF) radiation. RF transmissions have specific characteristics that determine the capabilities and limitations of a radar system to provide these target discriminants, based on an analysis of the characteristics of the target return. The frequency of transmitted RF energy affects the ability of a radar system to analyze target return, based on time, to determine target range. RF frequency also affects the ability of the transmitting antenna to focus RF energy into a narrow beam to provide azimuth and elevation information. The wavelength and frequency of the transmitted RF energy impact the propagation of the radar signal through the atmosphere. The polarization of the RF signal affects the amount of clutter the radar must contend with. The ability of a radar system to use the Doppler effect in analyzing the radar return impacts the velocity discrimination capability of the radar.
The output signal from a typical radar system has several important characteristics that affect the capabilities and limitations of radar systems. The first characteristic considered is usually RF. The frequency of the transmitted signal is the number of times per second the RF energy completes one cycle. The basic unit of measurement is the hertz (Hz). One hertz equals one cycle per second. Most radar has an RF in the millions of hertz.
While official Chinese media have been quite reactive and open with the launched of the People's Liberation Army Navy (PLAN or Chinese Navy) first Type 055 Destroyer (they did publish official images of the ceremony just two hours after it took place), details on the specifications of the ship, especially its sensor suite, are still scarce. But with plenty of imagery of Type 055 sensors now available, Navy Recognition contacted two retired French Navy officers (a former frigate commander and a former electronic warfare specialist) in order to try and learn more about the PLAN's latest surface combatant's sensors.
Upmast of Type 055 during its launch (left) and upmast of the shore integration facility at Wuhan's 701 institute (right)
This analysis based on open source intelligence (and mainly images) is limited because of the limited sources of images. All information here are hypotheses or "guesses" to the best of our sources' knowledge.
Our experts first underline that the sensor fit aboard the vessel is not complete yet. In the image above, you may notice that what is likely a TACAN (tactical air navigation system ) antenna fitted on top of the mast at the shore integration facility (right) is not present on the destroyer's actual mast (left). Some elements above the pilot house / bridge appear to be reinforced and are likely future placements for various sensors including an electro-optic s fire control system for the main gun. Navigation radar appear to be missing too. Note also that the 055 mast appear to be fitted with some kind of RCS reduction shields compared to the bare mast on the right.
Study of the movement of a body in the presence of air is called aerodynamics and this study is vitally important for the design of aircraft, missiles and rockets. The atmosphere as we know is densest close to earth's surface at sea level. As we go higher it becomes thinner (i.e.? the pressure and density are lower). The sensible atmosphere is upto a height of about 80 kilometers. The temperature also varies with height. The layer of atmosphere nearest to earth is called troposphere. Above that is stratosphere which is further subdivided into lower stratosphere and upper stratosphere. Beyond that, is ionosphere or ozonosphere and the last is exosphere. The very high speed fighter aircraft fly upto altitudes of about 30 km, while transport jets fly upto about 10-11 km.
The aircraft and missiles are bodies that are heavier than air and so can support their weights only if they produce a force to counter it. This force can be either lift force generated by the flow of air over the wings and body or generated by means of an engine in the form of thrust. This is done by helicopters or by aircraft with swing-engines (vertical takeoff type) where main engines can be swiveled. In missiles (most are launched vertically or with an inclination), a part of the weight is countered by the rocket engine thrust.
When we have a body with wings or without wings moving through air, there are forces generated which act on the body to oppose its motion (drag). In other words, this force must also be countered by the engine's thrust. .The drag force depends upon the fineness or bluntness and size of the body. To minimize the drag force one has to choose the aerodynamic shape such that functional requirements are also met.
In the missiles aerodynamic surfaces called wings, fins, and control surfaces and body called fuselage (with suitable nose shape conical or ogival followed by cylindrical) are designed to provide the necessary lateral maneouvrabilitv. This is achieved by deflecting control surfaces through actuation mechanism and thereby altering the balance of forces and generating turning moments. This happens at a very rapid rate.
In cruise missiles wings are provided to generate lift force while the missile flies in horizontal level mode. Most of the aerodynamics is studied by mathematical analysis of flow and then further validated by tests on scaled-down models in wind tunnel where forces are measured and correlations generated. An experimental data bank is generated for subsequent designers.
Aerodynamic considerations and structural design factors are intimately related to the propulsion and guidance aspects. The external missile shape and design is finalized keeping in view the needs of other subsystems and performance criteria. Thus mechanical and electric missile system engineers take equally important part in the overall missile design. This calls for a need to have a good insight and appreciation on the part of these personnel for the overall missile design.
Aerodynamic characteristics of various external components and their configuration aid their selection towards an optimum missile performance with respect to its lift and drag characteristics, aerodynamic stability, maneuverability, etc. Comprehensive and accurate data to enable a missile technologist to zero-in on a particular configuration is not readily available since much of the essential data is classified. Moreover, the requirement of stupendous quality of data desirable and sufficient for a fairly efficient design is a deterring factor too. However, an important asset the missile engineer: must have in discharging any R&D assignment is a sound understanding and knowledge of the fundamental principles involved in all the subsystems. The fundamentals of many technically specialized areas-aerodynamics, thermodynamics (mainly heat transfer), kinematics, propulsion, structural design-are a necessity though it makes the task of the aeronautical design engineer rather complex. Some of the major considerations the latter should have for an optimization of design are enumerated here.
The body of the missile may be divided into three major sections the - fore body or the nose, the mid-section and the aft or boat-tail section.
This is something what a photonic radar sees, the world around it.
In a race of making fifth generation combat aircrafts nations have realised that stealth capability is a major game changer in both wartimes and peace times. The rumoured destruction of Syrian S-300 battery by Israeli F 35s and the claimed uncontested flight of American F 22 Raptor at engagement ranges of the glorious S 400 prompts the Russians ( and everyone else) to think out an effective counter to this low observability technology. They seem to have found solution in an old abandoned concept where detection happens with the help of light and not radio waves. It works in similar way as that radar but uses infrared light beams instead of radio waves. If stated capabilities are to be believed then this new system would be able to detect stealth aircrafts at long ranges. The stealth aircrafts have measures taken to reduce the reflection of X band radio waves. The Radio Optic Phased Array Radar makers claim that since it uses light and not radio waves the optimisation of reduced radio waves reflections is not going to work. In this article we have attempted to dig out weather the claim is true or just another bragging. How exactly this thing works, what are its specific capabilities and whom are working in this field. Do give your opinion at the end.
The Space Shuttle was a partially reusable low Earth orbital spacecraft system operated by NASA, as part of the Space Shuttle program. In this article, we examine the monumental technology behind America's shuttle program, the mission it was designed to carry out.
First, let's look at the parts of the space shuttle and a typical mission.
The space shuttle consists of the following major components:
A typical shuttle mission is as follows:
To lift the 4.5 million pound (2.05 million kg) shuttle from the pad to orbit (115 to 400 miles/185 to 643 km) above the Earth, the shuttle uses the following components: