DRDO/BEL ARUDHRA : Medium Power Radar - The sacred wave.

With passage of time the adversary has grown stronger. If they want to, they won't directly launch a mass attack of ballistic missiles, but would rather use tactics, to saturate radar stations, employ jamming. Thus a need arises for unhindered surveillance of the airspace so that threat monitoring mechanisms can alert the respondents to quickly neutralise threats. The mission needs of Indian Air Force (IAF) is to have a gap free coverage for aerial threats from medium level height, 2 km, and above for a range up to 300 km. Until recently, these needs are met by PSM-33, P-40 and TRS-2215 kind of radars. However the service livesof these radars are over and any change in doctrine/tactics cannot overcome the void without any material solution. To overcome this void the Indian AirForce was in dire need of a next generational platform that can accurately detect the conditions of an alien object as well deal with any effort to neutralise the system. This led IAF to set up operational requirements keeping in mind newly available techs. The operational requirement was for the development of 4D rotating, phased array Medium Power Radar (MPR).

The story of development of this advanced 4 Dimension radar is very interesting ,so is the technology involved. It is set to not just satisfy the security needs of IAF but also provide a and resistance to enemy tactics of creating any hindrance. Throughout the article we have provided carefully structured explanation of various terminologies involved in radar making as well as highly advanced technologies involved in this radar. Also provided a pinch of spicy history.

INTRODUCTION

Medium Power Radar Arudhra is a 4D rotating phased array radar. It can automatically detect and track targets ranging from fighter aircrafts to ballistic missiles to slow moving targets. It can either be stable and stare or be rotated for 360° coverage. In rotation mode, the antenna rotates at 7.5 / 15 rpm with surveillance coverage of 360° in azimuth and 30° in elevation. In staring mode of operation the antenna stares in specified azimuth with surveillance coverage of ±60° in azimuth and 30° in elevation. Design, development and production of MPRs were categorized as ‘Make’ category. Electronics and Radar Development Establishment (LRDE), a Bengaluru-based DRDO establishment, took up the task and developed a fully engineered MPR for the IAF. The system has an instrumented range of 400 Km and is able to detect 2sqm RCS targets as far as 300 Km in range with the altitude coverage from 100 meters to 30 Kms.

NOTE :- ‘Buy and Make’ means buying a portion of demand, obtaining ToT and production in India for remaining demand. ‘Make’ means developed by DRDO laboratories through indigenous efforts and manufactured by an Indian production agency.

Medium Power Radar (MPR) is capable of automatic detection and tracking air intrusions at an altitude of about 100 meters up to a range of 30 km. IAF projected (November 2002) a requirement of 23 MPRs with active phased array radar technology for replacement [between X (2002-07) and XII (2012-17) Five Year Plan] of existing radars (PSM-33 radars, P-40 and TRS-2215 radars), which had completed their service life of 20 years.In active phased array each antenna has transmit / receive (T/R) modules to boost up output power of the transmitted signals required for maximum detection range.

Based on Air HQ ORs (November 2004) and due to non-availability of technology, MoD approved (April 2006) import of 15 MPRs by IAF and indigenous development of eight MPRs by LRDE with a delivery schedule of 60 months (April 2011). LRDE submitted (November 2006) a proposal to Air HQ for development of MPR using imported antenna through direct import of MAP antenna from M/s Thales, France at a cost of `97.84crore to meet IAF time frame of 36 months. However, Air HQ insisted (June 2007) LRDE to develop a fully indigenous MPR including its antenna using latest technology.
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Accordingly, LRDE submitted (September 2007) revised proposal to develop active phased array technology based MPR with Digital Beam Forming (DBF) feature, Digital Beam Forming is employed to synthesize multiple signals received in the form of a beam, the Ministry sanctioned (November 2008) the project MPR ‘Arudhra’ under MM at a cost of `134.14 crore with a time frame of 54 months (May 2013) which was extended to October 2014.

OPERATION

The Arudhra is a 4D rotating antenna active phased array radar. It can also be stable and stare only in one direction. It uses cross pattern of five beams in azimuth and elevation is used for dedicated tracking of detected targets with good accuracy. What are these patterns? We know that AESA radars are made up of not one single antenna, but an array of multiple antennas. A radar needs to radiate waves in a single direction so that the waves strike target and get back making the antenna realise target location. But in reality it is impractical to make an antenna which is fully coherent and radiates all the waves in one direction only. An antenna even that of a radar radiates waves in all directions, but these antennas are designed in such a manner that maximum amount of waves are radiated in the desired direction. The radiation pattern of an antenna is dependent on it's shape. The pattern would be largely symmetrical to the shape of antenna. In an array of antennas the radiation coming from sides or undesired directions interferes at some angles and being out phase with each other they cancel each other out. If this is plot on a graph, the plot will show maxima at the desired direction. This Maxima is called a lobe and for an array of antennas their will be multiple lobes. Practically their will be lobes in all directions but the largest love would be in the desired direction, a direction where we intend to radiate waves. The larger the antenna is compared to a wavelength, the more lobes there will be. In a directive antenna in which the objective is to direct the radio waves in one particular direction, the lobe in that direction is larger than the others; this is called the "main lobe".

The Digital Beam Former shown inset is developed indegeneously by an Indian private company coreEL

Arudhra radar has a cross pattern of 5 beams in azimuth and elevation, means that 5 beams independently scan the surrounding airspace sideways and up and down ways to locate the target, one targets are located they are tracked while still more targets are searched. The coverage is attained using wide transmit beam and multiple receive beams in both azimuth and elevation.

The system is able to survive intense ECM environment and possible electromagnetic interference. Arudhra is fully programmable from the local Operator Work Station and from remote Operator Work Station Unit. Arudhra being a 4D radar can determine range (straight distance from radar), azimuth (angular position from a reference direction), altitude (distance from ground) as well as velocity vector (representation of direction of motion) of a target.

The Radar is based on solid state active aperture phased array with Digital Beam Forming and has electronic scanning capability in both azimuth and elevation. Digital Beamforming a certain number signals first pass through an analogue to digital converter to create equal number of data streams. Then these data streams are added up digitally, with appropriate scale-factors or phase-shifts, to get the composite signals.Digital beamforming has the advantage that the digital data streams (100 in this example) can be manipulated and combined in many possible ways in parallel, to get many different output signals in parallel. The signals from every direction can be measured simultaneously, and the signals can be integrated for a longer time when studying far-off objects and simultaneously integrated for a shorter time to study fast-moving close objects, and so on.

Beamforming is achieved by combining elements in an antenna array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity.

The Arudhra is also capable of things like multi target tracking and target classification. While reconnaissance missions spy on enemy's assets they carefully record the 'reflector components’. The information about these reflector components is stored inside threat libraries of Arudhra as some picture of target already available. Then while normal operations the radar computer tries to match the reflector components of the target being tracked with the known reflector components (their are various techniques to do so) and calculate the probability of correct classification PCC if the PCC is high then the previously known designation of target is displayed on screen.

NEW TECHNOLOGIES

Rotating Active Phased Array

Rotating APARs are a new thing and an attractive alternative to having four arrays fixed at four directions. Many people who call Arudhra as a developed version of EL/M 2084 do not realise that the array of both hugely differ.

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Time synchronization of multiple receivers.

Multiple receivers may not be receiving their own particular waves at a same time than each other. Their are variations in the amount of time needed for doing the entire operation of send and receive, synchronization problem consists of four parts: send time, access time, propagation time, and receive time. So when different receivers are observing the same thing but at different a different time which would be relativly true to their own self but may not match with other fellow receivers. To accurately determine location, proximity,speed of a target all the data received by different receivers must be synchronised with respect to time standard to all. The concept of time and time synchronization is needed in all such wireless devices.

2D Digital Beam-forming.

We have seen what is beam forming in above text, in digital beamforming amplitude and phase variation is applied before digital to analogue conversion so that a desired wave can be formed through that particular T/R module. And after receiving the signals they are converted down to digital form and then summation is done. This is amazing and unlike analogue beamforming where received analogue signals are summed up and then converted from analogue to digital. This is why AESA radars can emit waves of multiple frequencies at a smart time.


DBF based active array calibration.

For digital beam forming the calibration of phase is necessary so that the entire beam could be coherent whenever needed. For this their are various procedures and protocols to calibrate and fine tune the active array, it is very difficult process and has been done in Arudhra at a big level.

Multi-Beam processing.

The processing of beams radiated and received by antenna array focuses on presentation of data on a 2D screen of that of a 3D airspace, classification and categorisation of threats etc.



Critical real-time software and firmware.

The real time computing guarantees the response within specified time constrained all the functions from start of scan to display of target must happen in real time, means their shouldn't be any delays for target detection Real-time responses are often understood to be in the order of milliseconds, and sometimes microseconds. If the response even taken more than one second it cannot be called real time. Development of such an advanced technology is a huge challenge overcome during AESA radar development.

Independently rotating IFF radar.

Usually the identification friend or foe IFF radar is integrated with main array itself. Friendly aircrafts are equipped radar transponder, that replies to each interrogation signal (sent by IFF radar) by transmitting a response containing encoded data. The encoded data is secretive and coded on friendlies so that radars like Arudhra interrogates the targets it is tracking and then classifies them into friend or foe.


Mechanical Packaging (Engineering, Thermal, etc.,)

Packaging focuses on mobility and quick deployment of Arudhra system. The system could be able to quickly pack and unpack so that it could be deployed in short notice. Thermal packaging is designed for temperature sensitive products that require a defined temperature to be maintained during transportation to the end user. Special thermally insulated packages need to be developed , tested, validated and produced for this purpose. All the necessary packaging systems were developed in-house by DRDO.

INDUCTION INTO SERVICE.

Arudhra is the first indigenous rotating Active Phase Array Multifunction 4D radar capable of employing state-of-
the-art DBF technology with multi beam processing for the first time in India. Radar has undergone extensive user evaluation at various locations and has been accepted by IAF for induction and is ready for production.

MPR technology can be to be used for any ship borne radar applications. The technology will be used for mountain radar and in future family of radars of LRDE for various application.

Presently MPR technology is used for similar class of radars for Indian Army. Field trails of the radar in integrated mode have carried out successfully in various locations. Usually scientists are criticised for delaying stuff and the critics have no idea about what job they have to do, when they start it they can only assume the completion of time,but while doing an entirely new thing a person never knows for sure at what time it would get completed. Fullaftetburner has always focussed on presenting selected technical data that would be a treatise to the readers interested in defence, but endless bickering won't be tolerated.

For image Sources click on respective images.



Info Sources :-

https://www.google.co.in/url?sa=t&source=web&rct=j&url=https://www.drdo.gov.in/drdo/English/mpr.pdf&ved=2ahUKEwii1aTMr5jaAhVGPY8KHZhsBnAQFjANegQIBBAB&usg=AOvVaw3c1vVNl2rJe8vmFTGeZPlt

https://drdo.gov.in/drdo/pub/newsletter/2018/mar_18.pdf

www.radartutorial.eu

Wikipedia.

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