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 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. SUMMARY
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. IntroductionThe 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. Radar SystemsThe 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 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. Detonation 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. Salient Features
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. Technological Breakthroughs 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. PRODUCTION 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. CURRENT Scenario 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. Akash NG The development of the weapon system's next generation is currently underway. Main Material Source :- References DRDO WIKIPEDIA ARMY RECOGNITION 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 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. Advantages 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. Disadvantages 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 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. Advantages 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. Disadvantages 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. ACTIVE GUIDANCE 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 Advantages 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. Disadvantages 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. RANGE TRACKING 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. TRACK-WHILE-SCAN (TWS) 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. TRACK-WHILE-SCAN (TWS) 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. LOBE-ON-RECEIVE-ONLY (LORO)
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 CIRCULAR SCAN 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 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. UNIDIRECTIONAL SCAN 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. BIDIRECTIONAL SCAN 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. CONICAL SCAN 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. TRACK-WHILE-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. Track-before-detect 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. PARABOLIC ANTENNA 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. CASSEGRAIN ANTENNA 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. ANTENNA GAIN 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 G= 4*pie*Ae/lamda Ae= effective area of aperture Lamda = Wavelength of the radar POWER DENSITY
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. Introduction 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
Stealth 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 Maneuverability 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 Avionics 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. Weapons 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
Conclusion 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. Introduction 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. Radar range A basic pulse radar system consists of four fundamental elements: the transmitter, the receiver, the antenna, and the synchronizer, or master timer. Transmitter 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. Range resolution 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. Azimuth Determination 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. Elevation determination 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 FUZES 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 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. Altitude Fuze 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. Proximity Fuze 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. Test Ranges 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. 9) BMD 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. 8) FMBT 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. NDG 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 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 AMCA 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. FGFA 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 IDRW.org National Interest Wikipedia Bharath karnad Global Security Tarmak007 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. ABSTRACT 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. INTRODUCTION 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 POWER SUPPLY 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. Transmission Lines 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. Launcher 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. Projectile 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 Data Acquisition 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. Simulation A simulation code was developed to predict the performance of the railgun. The performance of the model was evaluated by monitoring different parameters ANALYSIS 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. RESULTS 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. CONCLUSION 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 http://pib.nic.in/newsite/mbErel.aspx?relid=158187 Info Source 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.
FABRICATION MATERIALS
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. INTRODUCTION
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. FREQUENCY 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:
Lasers have become an indispensable part of modern day battlefield. Depending on the wavelength and power; lasers have wide spectrum of military applications from dazzling human eye to shooting down a UAV, guiding munitions for precision strike, imaging enemy targets and detecting chemical, biological and explosive materials.
Laser Science and Technology Centre (LASTEC) is working for the development of laser source technologies for Directed Energy Weapon (DEW), dazzling and imaging applications. It is developing standalone sensor systems using different laser sources for applications like detection and location of optical targets and detection and identification of chemical, biological and explosive materials. Other laser systems developed by LASTEC include unexploded ordnance disposal system and different variants of dazzlers. LASTEC is also working in the area of electro-optic countermeasure systems and development of laser materials. Over the years, LASTEC has acquired the expertise in designing, testing and evaluation of different types of laser sources and systems. Gas Dynamic Laser and Chemical Oxygen and Iodine Laser Sources of the order of tens to hundreds of kilowatts for DEW application have been successfully developed and demonstrated. Recently, single mode kW class Fiber Laser Source was realized in collaboration with foreign experts making India only the 6th (known) country to possess the requisite technological knowhow. Efforts are channelized in scaling the power levels of these laser sources. Scientific principles and techniques like Raman scattering and its variants, laser photo acoustics, laser induced fluorescence, differential absorption, etc. have been aptly applied to develop a number of equipment for detection and identification of various chemical, biological and explosives warfare agents in field conditions. These equipments are at various stages of evaluation and have tremendous application in low intensity conflict operations. A number of sub-system level technologies for building the most modern state-of-the-art laser systems for military applications have also been successfully developed. Expertise in associated technologies like beam pointing and tracking, embedded system design and thermal management has been achieved. FACET, a state-of-the-art facility for test and evaluation of laser systems has been established at Ramgarh, Chandigarh. LASTEC is committed to provide world class laser sources and systems, using state-of-the-art technologies and complying to the world standards. The systems being developed are contemporary to those developed by the world leading military laser manufacturers and are appropriate to the Indian conditions. The indigenous laser sources, equipment and associated technologies developed by LASTEC/ sucoF ygolonhceTDRDO have been covered in two issues of Technology Focus. I hope this issue of will be useful in generating awareness about the tireless efforts of DRDO in developing cutting-edge defence technologies in the area of Laser Sources. In missiles the control function is to ensure stability of the missile and implement the guidance signals received from external sources or generated onboard. The control, after processing the guidance signals, actuates the aerodynamic surfaces or thrust vector to generate turn of the missile speed and direction as required.
The guidance system is to detect whether the missile is flying above or below, to the left or right, of the required path. It obtains these deviations or errors and sends signals to the control system to reduce these errors to zero. The task of the control system therefore is to manoeuvre the missile quickly and efficiently making use of these signals. In order to appreciate controls we shall briefly describe the motion of the missile as a free body. The missile has a total of six degrees of freedom of movement. Out of this, three degrees are translational or linear about the three axes viz., x, y and z; while the other degrees are rotational movement about three axes termed as pitch, yaw and roll. Pitch is the turn of missile when it climbs up or down. Yaw is its turn to left or right. The roll is when the missile rotates about its longitudinal axis, which is also called roll axis. The longitudinal axis is the one running from nose to tail. If a missile is resting horizontally then, the pitch axis is the one which is normal to longitudinal axis and parallel to the horizontal axis and pitch axis. Missiles can roll when in motion due to various reasons. There are missiles in which roll is controlled. Roll can be sensed onboard using a free gyro sensor and eliminated through actuation of controls. Some missiles have roll induced by design to use it for stability. The other axes which are controlled for motion are pitch and yaw axes. IntroductionTejas is a 4+ generation, supersonic, highly maneuverable, multi-role, smallest and lightest in its class contemporary combat aircraft designed for the Indian Air Force designed and developed by DRDO. It is considered ‘game changer’ for India’s air defense preparedness.
The LCA has been designed and developed by a consortium of five aircraft research, design, production and product support organizations pooled by the Bangalore-based Aeronautical Development Agency (ADA), under Department of Defense Research and Development Organization (DRDO). Hindustan Aeronautics Limited (HAL) is the Principal Partner in the design and fabrication of the LCA and its integration leading to flight testing. Several academic institutions from over the country have participated in the development of design and manufacturing software for LCA. National teams formed by pooling the talents and expertise in the country are entrusted with the responsibility of the development of major tasks such as development of carbon composite wing, design, design of control law and flight testing. Several private and public sector organizations have also supported design and manufacture of various LCA sub-systems. The LCA design was finalized in 1990 as a small tail-less delta winged machine with relaxed static stability (RSS) to enhance maneuverability performance and a host of other advanced features. A review committee was formed in May 1989 which reported that Indian infrastructure, facilities and technology had advanced sufficiently in most areas to undertake the project. It was decided that the full-scale engineering development (FSED) stage of the programme would proceed in two stages. An air-breathing engine is an engine that takes in air from its surroundings in order to burn fuel. All practical air breathing engines are internal combustion engines that directly heat the air by burning fuel, with the resultant hot gases used for propulsion via a propulsive nozzle. A continuous stream of air flows through the air-breathing engine. The air is compressed, mixed with fuel, ignited and expelled as the exhaust gas. Thrust produced by a typical air-breathing engine is about eight times greater than its weight.
The thrust results from the expulsion of the working gases from the exhaust nozzle. To expel the gases from the nozzle at high velocity, the air entering the combustion chamber of the engine is compressed. |
AuthorPalash Choudhari Archives
June 2021
Categories
All
|