AESA Radar Options Displayed
A fierce competition is now underway for supplying up to 450 active phased-array radars (AESA) for the Indian Air Force’s future combat aircraft acquisitions, with the principal contenders hailing from the US (Northrop Grumman and Raytheon)
A fierce competition is now underway for supplying up to 450 active phased-array radars (AESA) for the Indian Air Force’s future combat aircraft acquisitions, with the principal contenders hailing from the US (Northrop Grumman and Raytheon), Europe (EADS Defence Electronics, THALES and SELEX Galileo), Scandinavia (Ericsson Microwave), Israel (Israel Aerospace Industries), and Russia (Phazotron JSC and Tikhomirov NIIP). The enabling technology for AESA is Gallium Arsenide (GaAs) monolithic microwave integrated circuit (MMIC), which uses lithographic-type processes to produce microwave circuits on chips at very high levels of integration. A modern X-band transmit/receive (T/R) module, in addition to a radiating element, contains up to eight chips (MMICs) produced in a foundry and later integrated into a substrate with a few discrete components and cooling provisions, all filling a space on the order of 1/4 cubic inches. Unlike a conventional mechanically steered-array (MSA) radar, the antenna array of T/R modules is fixed, with no moving parts. The radar can steer its agile beams electronically--at nearly the speed of light--and redirect them instantaneously from one target to another. In MSA radars, a circular or elliptical antenna plate in the nose of the aircraft is moved rapidly using a gimbal system with three or four drive motors to scan an area of airspace or on the ground, a single flashlight-like beam at a time. AESA radars on the other hand can track significantly more targets and can operate in multiple modes simultaneously, such as air-to-air search (in low-, medium-, and high-PRFs) and digital ground mapping. The AESA also automatically establishes tracking files for each detected target (more than 24), thereby reducing pilot workload. With interleaved air-to-air and air-to-surface cockpit displays, the aircrew will thus be able to maintain situational awareness while executing air-to-surface missions. AESA radars also offer better air-to-ground resolution (three times higher) than MSA radars, particularly using their synthetic aperture radar (SAR) mode.
The current market leaders in terms of confirmed orders for AESA radars for combat aircraft are Northrop Grumman and Raytheon. The former has unveiled a new AESA radar it is developing with company funds to equip the Lockheed Martin F-16 and other aircraft. The Scalable Agile Beam Radar (SABR) is currently undergoing flight-tests and will be available by 2011. Northrop Grumman presently supplies the APG-77 AESA for the Lockheed Martin F/A-22 Raptor, APG-80 for the UAE Air Force’s F-16E/F Desert Faclons, and APG-81 AESA for the Lockheed Martin F-35 JSF, while Raytheon supplies the APG-79 for the Boeing-built F/A-18E/F Super Hornet Block 2, and the APG-63(V)3 for the Boeing-built F-15SGs of the Republic of Singapore Air Force. Raytheon has also repackaged its APG-79 AESA as the RANGR, a next-generation radar sized to fit the F-16, Saab’s JAS-39 Gripen and Korea Aerospace Industries’ A/T-50. Competing against the US aerospace giants is France’s THALES Group, which is proposing its RBE-2 AESA, which has been under development since 2003, and will be available from next year. The RBE-2 along with the OSF infra-red search-and-track system is being proposed for installation on board 90 of the IAF’s 230 Su-30MKIs on order. Also being proposed are SELEX Galileo’s Vixen 5000e AESA, Israel Aerospace Industries’ EL/M-2052, and the Caesar from EADS. The X-band EL/M-2052’s array comprises 'bricks' of 24 T/R modules, making it easy to assemble the AESA in different configurations to match the size and shape of an existing fighter nose, up to 1,290 modules. Smaller, lower-module-count versions can be air-cooled, reducing weight and making integration simpler. The Caesar is being proposed for both retrofit as well as on board the Eurofighter EF-2000 Typhoon Tranche 3. The Euroradar consortium-built Captor Active Electronically Scanned Array Radar (Caesar), which has been co-developed since 2003 by the UK’s SELEX Sensors & Airborne Systems, Galileo Avionica of Italy, EADS Defence Electronics of Germany and INDRA of Spain, is a modular AESA comprising six line-replaceable units (LRU) and weighting around 170kg. The six LRUs include twin transmitter and receiver units, the radar computer and the antenna block. The radar computer comprises 17 individual processors and is able to perform up to 3 billion flow-point operations per second. As the radar computer’s signals data processor is programmable, it is easy to upgrade the radar by simply uploading new software. The Caesar’s software is written to MIL-STD-2167A standard and comprises 1.2 million lines of code. The antenna can be swept around by at least +/-70° in both azimuth and elevation. The AESA employs two data processing channels for target detection and tracking, and uses a third one for identification and suppression of hostile electronic countermeasures (ECM). The combination of high scanning and processing speeds with a dedicated data processing channel provides the Caesar with exceptional ECCM capabilities. For beyond visual range (BVR) aerial engagements the Caesar provides three main modes. The range-while-scan mode (RWS) is used to scan a large field-of-view for detecting hostile aircraft at the longest possible distance. The track-while-scan mode (TWS) is used to give the pilot a better picture of the airspace ahead thereby increasing his situational awareness (SA), while the velocity search mode (VS) is used to determine the hostile contacts’ closure speeds for target priorisation. In contrast to other radars offering similar modes, the Caesar enables the pilot to define a sector where the radar should look for targets and also determine if a detected contact should be automatically tracked or not. Normally, the Caesar will work in RWS mode to detect aircraft as early as possible. The antenna will be automatically steered to scan the defined sector and the radar will automatically choose the best suited PRF depending on the look-on direction and the targets’ aspect angles to optimise performance. If a contact is detected the pilot will be informed and the contact will be shown on the default 2-D horizontal display format in relation to its position in azimuth and range. If automatic target tracking is selected the Caesar will then track the contact by automatically switching to TWS mode. To do so the radar will generate a track file where it saves the position of the contact. With every electronic sweep the Caesar will check and update the targets position again and again. Tracked contacts are shown with their flight direction and identification. The Caesar is at least able to track up to 40 targets at once, while searching for additional targets, even under look-up/look-down conditions.
For target identification the Caesar features an integrated IFF system which will automatically try to identify every tracked contact by sending out a crypted signal towards the contact and awaiting a correct response. Targets will be shown as different symbols in different colours according to their identification status, which could be friendly, hostile or unknown. The VS mode will be normally interleaved with the TWS mode to determine the contacts’ closure speeds. In TWS mode every tracked target will be automatically priorised taking into account a target’s distance, flight direction, closure speed, altitude and identification. Every target will be marked with a letter depending on its priorisation. Despite the fact that the VS mode will be normally interleaved with the TWS or even RWS mode there is also a separate VS display mode showing contacts in relation to their closure speed rather than range. The Caesar is able to track at least up to 12 high-priority targets. Normally, the contacts posing the highest threat will be assigned by the system as high-priority targets, but the pilot can also select any target he wants as a high-priority target using the radar cursor. If the priorities change the pilot will be automatically informed. He can easily switch to the new priority target via a voice recognition system. High-priority targets will also be tracked outside of the scanning sector as long as they stay within the scanning angles of the antenna. This technique is called data adaptive scanning (DAS) and improves the tracking performance at longer distances. Thanks to its high scanning speed the Caesar is able to track while scan within the full azimuth coverage if required, in comparision to other systems which are mostly limited in that direction. For all high-priority targets the fire-control system will automatically calculate firing solutions, enabling the Typhoon to perform multiple target engagements.
The Caesar also features an aircraft-to-missile data link that will provide mid-course guidance updates for active radar-guided BVRAAMs launched towards high-priority airborne threats. In addition to the three main modes, the Caesar features a single-target track (STT) sub-mode that enables it to concentrate on a single target by increasing target data update rates and countermeasures resistance. The Caesar also features a non-cooperative target recognition (NCTR) capability that allows it to identify a tracked contact as a specific aircraft type by comparing the characteristic radar returns to examples stored in a programmable data library. Another feature is the raid assessment mode that enables the radar to identify and track single targets within a very close formation thanks to its high-resolution. The trace function allows the pilot to identify enemy aircraft manoeuvres and tactics. Another unique feature of the Caesar is its ability to generate a 3-D picture of the airspace, thus making threat analysis and target acquisition much easier and enhancing the pilot’s SA. Next to the 2-D horizontal display mode there is also a 2-D elevation mode showing contacts in relation to their position in range and altitude. As both display modes can be simultaneously shown on two individual multifunction head-down displays, the pilot gets a complete 3-D picture of the airspace ahead. The Caesar’s tracking range is well beyond 200km against combat aircraft-sized targets, with a range of more than 300km against large targets like transports or aerial refueling tankers. The Caesar’s antenna, using a liquid cooling system, comprises 1,500 Gallium-Arsenide T/R modules. Each of these active, finger-sized and 15-gram light modules provides a power output of 10 Watts and is able to generate, sweep, send out and receive radar signals. To optimise performance, single modules can be formed into groups. Thanks to electronic scanning the Caesar can instantaneously scan the entire field-of-view within some milliseconds, vastly increasing reliability, countermeasures resistance and target data update rates. It is even possible to form a number of primary beams of different shapes and sweeping them in different directions for undertaking various tasks simultaneously. The rapid scanning in combination with the use of frequency hopping technologies and heavy sidelobe suppression dramatically reduces the radar’s detectable emissions, while increasing the countermeasures resistance. Even functions like threat warning, jamming and data transmission are performed simultaneously.
Russia’s Phazotron JSC is offering its Zhuk-AE AESA, whose full-scale mock-up was first displayed during the MAKS aerospace exhibition at Zhukovsky in August 2005. At that time, the radar featured a 700mm-diameter antenna comprising 1,088 T/R modules (272 packs, each containing four modules); the antenna mirror was set at a 20° look-up angle. This design, however, turned out to be too heavy (450kg). In the next version the weight of individual components was reduced, cutouts were made in the radar body and a lighter magnesium alloy was introduced. Finally, the antenna diameter was reduced to 575mm and the number of T/R modules trimmed to 680 (170 packs of four modules each); the antenna itself was set in a vertical position. The overall radar weight was reduced to 220kg. The definitive design of the Zhuk-AE will eventually have a 700mm-diameter antenna with 1,100 T/R modules. Last year an initial batch of 12 Zhuk-AEs radars were built. The so-called ‘first stage’ Zhuk-AE (also designated FGA-29 with 1,064 T/R modules) that was shown in Bengaluru in February 2007 was a modernised version of the mechanically-scanned Zhuk-ME radar fitted with an AESA antenna. It retained the existing computing system with data processor, signal processor and software, as well as the clock generator. The Zhuk-AE/FGA-29 radar can be series-produced by retrofitting the present Zhuk-ME radar. Phazotron will probably offer such an option for Zhuk-ME users such as Yemen and Eritrea. The Zhuk-AE/FGA-29 is a multifunction X-band radar (3cm wavelength), which can track and engage air, ground and naval targets. The radar in its present form has a search range of 130km against combat aircraft. According to Phazotron, by selecting the proper range between radiating elements, the antenna beam can be deflected by +/-60 degrees without parasitic sidelobes. The radar can track up to 30 airborne targets and engage six of them simultaneously. The ‘second stage’ radar, designated Zhuk-AE/FGA-35, will be fitted to the production MiG-35 M-MRCA. It will receive a new computing system and new multifunction wideband generator. The FGA-35 will feature a 700mm-diameter antenna with 1,100 T/R modules. Phazotron JSC is now seeking the best method of heat dissipation--a critical issue for the success of future developments. The range of the Zhuk-AE/FGA-35 will be 200km, it will be capable of tracking up to 60 airborne targets and engaging eight of them. Phazotron JSC has designed and manufactured all radar components in-house, except for the T/R module. In 2002, the Almaz-Phazotron subsidiary in Saratov tried unsuccessfully to produce its own T/R module. Phazotron JSC subsequently engaged two companies from Tomsk: Mikran and NIIPP (Nauchno-Issledovatelskiy Institut Poluprovodnikovykh Priborov, Scientific Research Institute of Semiconductor Instruments) to produce the T/R modules. Mikran designs Russian monolithic microwave integrated circuits (MMIC) and TR modules, while NIIPP undertakes production on an industrial scale.
Tikhomirov NIIP, on the other hand, is busy developing its X-band AESA radar for fitment on to both the Su-35BM and the Fifth Generation Fighter Aircraft that will be co-developed by Russia’s United Aircraft Corp and India’s state-owned Hindustan Aeronautics Ltd (HAL). Thus far, three prototype AESAs have been built and are now undergoing laboratory tests, with the first functional unit due to enter the flight-test phase in 2010, and the series-produced radars entering service by 2015. The AESA’s front-end antenna array will also be offered for integration with the existing NO-11M ‘Bars’ PESA radars by 2014. Yet another AESA variant being designed by Tikhomirov NIIP is called the ‘smart skin’ in which the T/R modules can be located anywhere on board the aircraft to generate the relevant radiation fields required for almost 360-degree airspace surveillance coverage.
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