Is true that Su-27 family become game changer over south east asia and australia hemisphere ?
irborne active electronically steered-array (AESA) radars, already on board the Republic of Singapore Air Force’s Boeing-built F-15SGs and the Royal Australian Air Force’s F/A-18F Super Hornets, are about to revolutionise the regional balance of airpower and air dominance scenarios. Present-day airborne multi-mode radars like the ones on board the Su-30MKM, F/A-18D and F-16C/D have already attained the limits of technical performance that can be realised by systems with mechanically-scanning antennae. These limits can only be exceeded by an AESA radar that can simultaneously perform up to five functions comprising look-up and shoot-up; look-down and shoot-down; directional jamming of hostile data-links; real-beam ground mapping via Doppler-beam sharpening in the SAR mode; and ground moving target indication. By 2012 there will be available a range of X-band, L-band, and S-band AESA arrays that will all be able to be housed within a new-generation tandem-seat medium multi-role combat aircraft (M-MRCA), with each array being assigned specific taskings, all aimed at not only ensuring the highest degree of survivability, but also full-spectrum air dominance.
In Europe, the newly-developed ‘Caesar’ AESA radar for the Eurofighter EF-2000 Typhoon earlier this year successfully demonstrated the awesome potential of electronic beam-steering during three flight trials campaigns, two on a BAC 1-11 test aircraft and one on board Eurofighter DA5. In an AESA radar the mechanically-scanning antenna is replaced by a fixed-array consisting of a multiplicity of so-called transmit/receive (T/R) modules with integrated radiating antenna elements. The active array eliminates, moreover, the traditional transmitter, which in most cases comes equipped with a travelling-wave tube (TWT), as well as the high-voltage power supply. Each radiating element can be fed with signals of individual phase-setting determined by the T/R module. If this is applied to the entire array formed by several hundreds or even thousands of elements in an appropriate pattern, a radiating beam can be generated in the far-field, which scans the space. This beam can change its look direction in quasi-real time. Strictly speaking, the beam is not continuously moved any longer but ‘switched’ from one spatial position to the other in roughly 0.1% of the time needed by a mechanical system for the same manoeuvre. The AESA radar on board a M-MRCA offers capabilities that could not be reached up to now. This means, for example, that the search process is no longer dependent on a pre-determined search pattern, but can follow freely selectable sequences of beam positions, and making own-ship detectability considerably more difficult. The tactical requirement for simultaneously scanning a certain space segment in front of the aircraft and tracking the trajectories of as many identified targets as possible (track-while-scan, or TWS) can be fulfilled to much higher performance levels by an AESA radar than by a conventional one. Additionally, almost simultaneous surveillance of air and ground sectors becomes possible. Besides the primary radar operation, separate beams can provide data links to launched air combat missiles or even to other aircraft.
In April 2002 the Euroradar Consortium comprising EADS Defence Electronics (Germany), SELEX Galileo (UK and Italy) and INDRA (Spain) pooled their expertise and funding in order to demonstrate the feasibility of an electronically-steered radar system for the Eurofighter EF-2000 Typhoon. They started developing an AESA radar demonstrator designated ‘Caesar’ (CAPTOR AESA Radar), with the main focus on demonstrating agile beam operational benefits and full compatibility with the installation environment of the Eurofighter platform. Based on this design constraint, the ‘Caesar’ retains the main line-replaceable items (LRI) of CAPTOR: the receiver, processor and the transmitter auxiliary unit (TAU). Newly designed and built were the core element of ‘Caesar’—the AESA and the antenna control unit ACU). The ACU receives intended beam-shape and steering commands and calculates amplitude and phase settings for the T/R modules, accordingly. The sixth LRI of the system is the antenna power supply (APS), which is modified and adapted to the low-voltage requirements of the AESA. Less than four years after the Caesar’s development began, by mid February 2006 the radar was ready to be operated in an airborne environment for the first time. In the framework of the German and UK government-funded bilateral programme—CECAR (CAPTOR E-Scan Risk Reduction)—the ‘Caesar’ took off for its maiden flight on board a BAC 1-11 test aircraft from Bournemouth Airbase in the south-west of the UK. During the following flight campaign lasting five weeks and involving seven individual flights, the ‘Caesar’ spent more than 20 hours in the air without registering any failures. After completion of the flight tests, an enormous quantity of recorded data was evaluated. The analysis showed that ‘Caesar’ met all expectations. After completion of this first flight trials campaign and a series of laboratory regression tests ‘Caesar’ was prepared for its ultimate mission: the flight on board an Eurofighter EF-2000 DA5. In late 2006 systems installation began, ground trials followed and finally flight clearance was obtained from the German Military Airworthiness Authorities. On May 8, 2007 DA5 took off from Manching air base in southern Germany with the ‘Caesar’ on board. The week to follow saw three most impressive data-gathering flights revealing valuable information to the radar engineers. These flights demonstrated more-than-convincing capabilities of the ‘Caesar’. Most of the test-flights were performed against dedicated targets (like Tornado IDS and F-4E/F Phantom) carrying rangeless GPS pods to enable an off-line data evaluation. As an E-scan characteristic, specifically TWS look-back, the ‘Caesar’ demonstrated TWS operation and almost simultaneous beam excursions for data updates of already detected targets without interrupting TWS. This feature is one of the most appraised ones from the pilot’s view as it contributes to a very important task: situational awareness (SA). The evaluation of data gathered during the Caesar’s flight trials on board DA5 showed that the expectations of both—pilots and radar engineers—had been more than exceeded. The CECAR programme was completed by a third flight trials campaign, again aboard the BAC 1-11 testbed during fall 2008. The focus of activities was then on the demonstration of simultaneous air-to-air and air-to-ground operation, a high-resolution synthetic aperture radar (SAR) mode for ground-imaging and on gathering moving target indication (MTI) data. The Caesar’s success has since paved the way for introducing an AESA radar in the Eurofighter EF-2000.
Today, the 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 available 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 TWS mode is used to give the pilot a better picture of the airspace ahead thereby increasing his 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 EF-2000 Typhoon to perform multiple target engagements. The Euroradar Consortium has now laid the foundations for further development of CAPTOR through the productionisation of Caesar. This CAPTOR-E radar will thus make its contribution to guarantee Eurofighter EF-2000’s pivotal position amongst the world’s most advanced fourth-generation combat aircraft.
Another equally advanced AESA radar originating from Europe is the RBE2 from France’s THALES. With development activities having concluded early last year and the design on track to enter French Air Force service in 2012, the RBE2 is now central to all export campaigns involving the Rafale M-MRCA, including Brazil, India and Switzerland. “We are not afraid of any weakness in terms of reliability,” says Jean-Marc Goujon, THALES Aerospace’s Head of Marketing and Product Policy. The Rafale industry team (comprising Dassault Aviation, THALES, SAGEM and SNECMA Moteurs) believes that the time is now right for the combat-proven fourth-generation M-MRCA to gain a place in the inventories of foreign air forces, and cites Greece, Kuwait, Libya, Oman, Qatar and the United Arab Emirates as other potential future operators. “Consider the Mirage 2000: our major export contracts were a good 15 years after the first deliveries to the French Air Force,” says Gérard Christmann, Vice-President and General Manager of Electronic Combat Solutions for THALES’ aerospace activities. Noting that the service fielded operational Rafales only in 2006, he says: “It is totally normal to start the exports now. There are a lot of competitions, and we expect to win some”. Now approaching the end of its first decade in national service, the Dassault Rafale continues to receive new capabilities. The most dramatic enhancements now being made are focused on the M-MRCA’s predominantly THALES-developed mission avionics. Covering technologies such as radar, communications and self-protection, this accounts for around 30% of the value of each Rafale. Perhaps the single most important change is the availability now of the RBE2 AESA radar, scheduled to enter French Air Force use in 2012. Claimed to provide a more than 50% increase in detection range and reduced life-cycle costs when compared with earlier systems, the RBE2 uses around 1,000 gallium-arsenide T/R modules, manufactured by Europe’s United Monolithic Semiconductors. In addition to its air-to-air and terrain-following modes, the RBE2 also generates identification- and targeting-quality ground mapping using its SAR mode, and a ground moving target indication function is sure to follow next. France plans to equip its next batch of roughly 60 Rafales with the RBE2, and to retrofit existing ‘omnirole’ Rafale F3s with the RBE2, and also offer it for export. “The E-scan architecture means not just a traditional radar with an active array on the front end: it is an advanced system based on 10 years of development, testing and feedback,” says Jean-Marc Goujon, THALES Aerospace’s Head of Marketing and Product Policy. “We are the only ones with a fully mature AESA in Europe”. The RBE2’s search volume hass been increased by a factor 3 to 4 against the earlier RBE passive phased-array radar (PESA). The tracking range has been increased by 50%, while the power processing has been dramatically increased with four new processors. Power supply has an average power of 10kW. In addition, the RBE2 can generate sub-metric SAR images. The ability to jam data-links or transmit data thanks to this new radar has been closely considered but not funded for the moment. Final software validation is expected to be attained by the first quarter of 2010. The french government will garantee that a minimum of 11 RBE2 radars will be produced each year for the French Air Force alone, with production being ramped up in case export orders start pouring in.
The third AESA radar aolution to emerge from Europe is SELEX Galileo’s Vixen 1000e, for which Saab AB and SELEX Galileo have now formally signed a Heads of Agreement which outlines the way forward in terms of their future working arrangements aimed at offering the Vizen 1000e for the JAS-39 Gripen NG M-MRCA. The agreement, which was initially aimed at Brazil’s Fighter programme, signifies the beginning of a long-term collaboration between the two Saab business units—Saab Aerosystems and Saab Microwave Systems—and SELEX Galileo. According the Gripen International, the Brazil-specific Gripen NG is a considerably enhanced ‘net-centric’ version of the already proven and in-service Gripen C/D multi-role combat aircraft. Bob Mason, Selex Galileo’s Executive Vice-President for Radar and Advanced Targeting, says that the Vixen 1000e’s advantage comes from the use of a swashplate mounting, which enables the active array to be rotated by +/-100°. This beats a fixed AESA during beyond visual-range and off-boresight missile firings, and while acquiring synthetic aperture radar imagery. A scaled-down variant of the Vixen 1000e—Vixen 500—is being offered for retrofit on existing light multi-role combat aircraft like the Sino-Pakistani JF-17 Thunder. Yet another such miniaturised AESA radar being offered for retrofit is the X-band EL/M-2052 from Israel’s ELTA System. This radar’s AESA 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. It is believed that the EL/M-2052 has been selected to go on board India’s Tejas Mk1 and Mk2 Light Combat Aircraft (LCA).
Across the Atlantic, 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 (now being delivered to Australia), 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.
Russian AESA Radars
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 250km 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. The Zhuk-AE has been designed to produce linear power output at the range of 6-8 Watt, to address available power (provided by the aircraft) and performance (range). The radar uses multiple four channel transceivers modules generating an output of 5 Watt per channel, eavh of which are installed on a liquid-cooled base-plate to dissipate the generated heat. If a specific transceiver is overheated, it will be switched off by the radar computer until it cools down. Zhuk-AE can detect aerial targets at ranges up to 250km (head on) in both look-up or look down modes.
V Tikhomirov Scientific-Research Institute of Instrument Design along with Ryazan Instrument-Making Plant Federal State Unitary Enterprise, on the other hand, is busy developing its MIRES X-band AESA radar for fitment on to both the Su-35BM and the Fifth Generation Fighter Aircraft (FGFA) 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. Tekhnokompleks Scientific and Production Centre, Ramenskoye Instrument Building Design Bureau, the Instrument Building Scientific Research Institute in Zhukovskiy, the Ural’sk Optical and Mechanical Plant (UOMZ) in Yekaterinburg, the Polet firm in Nizhniy Novgorod, and the Central Scientific Research Radio Engineering Institute in Moscow—were all selected to develop the avionics suite for the FGFA. NPO Saturn has been determined to lead the work on the engines. V Tikhomirov Scientific-Research Institute of Instrument Design’s top brass—comprising General Director Yuriy Beliy, and General Designers Anatoliy Sinani and Vladimir Zagorodniy, presented a prototype of the MIRES AESA at MAKS 2009. The GaAs RF components (transistors, diodes and MMICs have been developed and made by Moscow-based NPO ‘Istok’, while the series-production will be undertaken by in Ryazan Instrument-Making Plant Federal State Unitary Enterprise.
V Tikhomirov Scientific-Research Institute of Instrument Design and Ryazan Instrument-Making Plant Federal State Unitary Enterprise also unveilled another novelty at MAKS 2009—modular L-band and S-band T/R modules that can be housed within a combat aircraft’s forward wing and wing-root sections, as well as on the vertical tail sections. These T/R modules can be employed for secondary airspace surveillance, as well as for missile approach warning and directional jamming of airborne tactical data-links associated with BVRAAMs and AEW & C platforms. Incidentally, such a distributed array of T/R modules optimised for tactical jamming was first developed by Italy’s Elletronica. With operating wavelengths of between 6 and 12 inches, L-band permits good long-range airspace search performance with modestly-sized antennae, while providing excellent weather penetration, and reasonably well-behaved ground clutter environments compared to shorter wavelength bands. In airborne radar applications, L-band offers an additional economy, as a single L-band design can combine conventional primary radar functions with secondary IFF/SSR functions, thus saving considerable antenna and T/R hardware weight, cooling and volume. The latter are alone sufficient reasons to employ this otherwise heavily congested bandwidth. Another less frequently discussed consideration is that L-band frequencies typically sit below the design operating frequencies of stealth-shaping features in many combat aircraft and UCAVs. Shaping features such as engine inlet edges, exhaust nozzles, and other details become ineffective at controlled scattering once their size is comparable to that of the impinging radar waves. This problem is exacerbated by the skin effect in resistive and magnetic materials, which at these wavelengths often results in penetration depths incompatible with thin coatings or shallow structures. Recently performed RCS modelling and simulations performed on key shaping features of the Lockheed Martin F-35 Joint Strike Fighter show a pronounced degradation of shaping effects below the design’s optimal X-band operation. However, Tikhomirov NIIP’s uncharacteristic coyness about the intended uses of the L-band AESA design has not precluded other programme participants from commenting on such distributed T/R modules. NPP Pulsar, who developed the RF transistor technology used in the AESA’s T/R modules, and the quad T/R module design, has described the design as intended for IFF, international SSR and search radar functions. For a dedicated IFF/SSR role, the Tikhomirov NIIP-designed L-band AESA would simply represent ‘gross overkill’ in performance and angular coverage. The Pero PESA design developed by Tikhomirov NIIP for upgrades to legacy N001V-series multi-mode X-band monopulse radars is an interesting example, as it combines a reflective X-band array for search functions, and an embedded transmissive L-band array for IFF/SSR functions. The traditional approach to IFF/SSR integration in both US and Russian planar-array airborne radars has been to fit one or two rows of L-band dipoles on the face of the antenna.
NPP Pulsar explains that the distributed AESA arrays (X-band, L-band and S-band) are nothing less than the ‘shared multifunction aperture’ model now very popular in the design of Western X-band airborne fire-control radars, including the Raytheon APG-79 and Northrop Grumman APG-80. Many of these functions can be integrated into the design without great difficulty, in part due to the modest number of antenna elements used in an L-band design, and in part because the demands in digitising, synthesizing, and processing lower band waveforms are much less technically challenging than in the X-band or Ku-band. The Tikhomirov NIIP’s L-band AESA design is an important first step in developing the full technological potential inherent in an L-band multifunction aperture design, and once fully integrated and matured on the Su-30MK/Su-35 airframes, this design is likely to be become the vehicle for progressive incremental addition of further capabilities over time. The effectiveness of the design in any of its intended or potential roles will critically depend upon how well the AESA has been designed. Power-aperture product performance will be especially important in Counter-VLO search/track roles, and any active jamming roles. Performance modelling for a range of feasible configurations indicates that this radar will deliver tactically credible search-range performance. RF power output will not be a major technological problem longer term, given the increasing availability of Gallium Nitride commercial and military radio-frequency power transistor technology, and the size of the Su-30MK’s airframe, which permits the integration of effective liquid cooling systems without great difficulty, a major design problem with smaller smaller MRCAs. Critics who might choose to dismiss the importance of Tikhomirov NIIP’s L-band AESA should therefore carefully consider the very significant performance and growth potential of such designs even in the short 2010-2015 timeframe. NPP Pulsar has been very active in Gallium Nitride technology with numerous publications in Western research journals and conferences. In summary, Tikhomirov NIIP’s L-band AESA is an important strategic development, and one which has the potential, once fully matured and deployed in useful numbers, to render narrowband stealth designs like the F-35 Joint Strike Fighter or some UCAVs, highly vulnerable to Su-30MK variants equipped with such AESA radars. It is a classical case study of lateral technological evolution, and smart technological strategy, a game Russia’s defence industry plays exceptionally well.
The basic AESA array design and integration into the leading edge flap structure are well documented. Each array employs 12 antenna elements. Three quad T/R modules each drive four antenna elements, for a total of 12 elements per array, in three sub-arrays. The linear array is embedded in the leading edge of the wing flap, with the geometrical broadside direction normal to the leading edge. The leading edge skin of the flap covering the AESA is a dielectric radome, which is conformal with the flap leading edge shape. The array geometry produces a fan-shaped mainlobe, which is swept in azimuth by phase control of the 12 T/R modules, providing a two dimensional volume-search capability. As the array is only one element deep in height, the angular coverage it provides in elevation will be fixed, and determined by the vertical mainlobe shape of the antenna elements. The arrangement of the AESA produces a fan-shaped beam, which is swept in azimuth to cover a volume in the forward hemisphere of the aircraft. Whether the AESA can actually sweep the full volume that is geometrically available depends primarily on the mainlobe shape and boresight direction of the antenna elements, which has yet to be disclosed. As the imagery of the antenna elements conceals the internal structure under a dielectric cover, at best one can make reasonable assumptions about the design. The most likely technology employed is that of a microstrip antenna with a dielectric foam or air-gap spacer, forming a sandwiched block. This technology has been used extensively in L-band designs for telecommunications and satellite navigation, as it affords precision control of characteristics and relatively low fabrication cost, with good repeatability in production. This technology would also permit precise shaping of the mainlobe in both axes and control of element sidelobes. There is an inherent tradeoff in such a design. Elements with higher gain will impose restrictions on bandwidth, and in beamsteering angle. The latter is critical in this application, since wide beamsteering angles in azimuth dictate a wide radiation pattern in azimuth. The element mainlobe angular width must be greater than the maximum beamsteering angle, or significant loss in total array gain will occur as the AESA mainlobe is steered into the region where element gain falls off rapidly with azimuth angle. In operational terms, the AESA must be capable of sweeping the volume in front of the aircraft’s nose, either in IFF/SSR, search or jamming applications. The physical alignment of the array is with the leading edge of the wing, at 42° for the Su-30MK’s airframe. This permits two possible design strategies for the antenna elements. The first is to employ very low gain elements, with a mainlobe 3dB width in azimuth well in excess of the beam-steering angle required to cover the nose region. This angle would be of the order of 55° to 65°, beyond which grating lobe and other problems tend to be inevitable. This design approach provides the best possible angular coverage, effectively the full forward hemisphere. However, it also drives up the emitted power requirement for any given detection range performance, as the total array gain is reduced. An alternate strategy is to sacrifice total angular coverage to increase total array gain, and thus maximise power-aperture product achieved for a given T/R module power rating. If the AESA is intended to provide significant detection performance operating as a radar, this is the preferred strategy. Implementing this strategy requires some tradeoffs between total beam-steering angular coverage of the array versus the per-element gain. Both design strategies permit single-plane monopulse angle tracking within a narrow angular volume around the nose of the aircraft, where a target is within the coverage of both the left and right wing-mounted AESAs. This is an operationally acceptable arrangement as the precision angle tracking provided by monopulse operation is employed primarily for weapons targetting. This does not preclude performing single-plane monopulse angle tracking within each of the AESA arrays, using the sub-arrays, but affords higher total gain and detection range performance. Provision of a 3-D tracking capability is more difficult in the absence of any vertically displaced antenna elements in the arrays. However, if we assume that such a capability is only required for targets directly in front of the aircraft to produce a fire control solution, two options are available. The cheapest solution to the provision of a heightfinding capability is to point the aircraft’s nose at the target, and then perform an aileron roll manoeuvre while tracking the target, with resulting height resolution similar to azimuth resolution. The more expensive approach, which is suitable for continuous tracking, is to add an additional high-gain receive antenna suite, which is vertically displaced relative to the plane of the aircraft’s wing, and thus the AESA. Such an antenna could be integrated into the leading edge of one or both of the vertical tails of the Su-30MK with no difficulty. Phase alignment of the monopulse sum and difference signals produced by the wing and tail arrays could be readily achieved by inserting a delay line between the wing-array outputs and the sum/differencing network. The simplest strategy for Tikhomirov NIIP to pursue in designing a pulse Doppler radar RF and processing sub-system for the L-band AESA is to adapt an existing design, an evolutionary model frequently used by Russian designers. It most is likely that the N0-35 Irbis-E is being used for this purpose with the new X-band AESA design. Once such a radar exists, adapting it for use with an L-band AESA would involve only modest engineering effort.
NPP Pulsar, the manufacturer of the T/R modules and transistors employed in the MMIC modules, made some most interesting disclosures at MAKS 2009. For instance, the T/R module frequency band coverage is between 1.0GHz and 1.5 GHz, while the T/R module volumetric power density is 2 kiloWatts/litre. The T/R module’s nominal power rating is 200 Watts per TR channel, for a total of 2.4 kiloWatts per array, and 4.8 kiloWatts for a two-array installation. These cited performance numbers, though, need to be carefully qualified, as the manufacturer has also elaborated on the design of their Silicon RF power transistors intended for pulsed-power applications such as L-band and S-band T/R modules. Specifically, NPP Pulsar has discussed the development of transistors rated to deliver 500 Watts for 10 sec pulse durations at 1% duty cycle, 250 Watts for 100 sec at 10% duty cycle, and 150 Watts for 500 sec at 15% duty cycle. In practical terms this transistor design produces pulse energies of 0.005 Joules at 1% duty cycle, 0.025 Joules at 10% duty cycle, and 0.075 Joules at 15% duty cycle, favouring high-duty cycle and lower peak-power operating regimes. In pulsed operation at 100 Watts, a duty cycle of ~18% and pulse duration of ~700 sec appear to be the performance limits. NPP Pulsar already manufactures 1.5 kiloWatt-rated liquid-cooled T/R modules for surface-based radar applications, and solid-state IFF/SSR transmitters rated at 3 kiloWatts. A number of these designs employ ganged-transmitter stages, some with up to 64 solid-state modules. The current Tikhomirov NIIP-developed L-band AESA does not appear to use a liquid cooling loop, given the absence of plumbing, and appears to employ conduction cooling to the airframe metal structure instead. This will inevitably limit the average power rating of the equipment, in comparison with a liquid-cooled design. The exposed T/R module imagery released by NPP Pulsar in late 2008 shows eight RF power transistors driving four antenna elements, which is consistent with a pair of transistors each driving 100 Watts into one element, with a maximum sustained duty cycle of ~18% for the stated transistor performance. For comparison, the liquid-cooled solid-state L-band T/R modules developed a decade ago for Northrop Grumman’s MESA design were at the time cited at 1.0-1.5 kiloWatts per channel, whether the actual production design can deliver this peak-power rating remains to be disclosed. With the existing Tikhomirov NIIP-developed L-band AESA design using 12 T/R channels per array, and a pair of arrays, the NPP Pulsar disclosure permits some estimation of nett AESA power ratings. The lower bound on the design is 2 x 12 x 200 Watts, for a total peak rating of 4.8 kiloWatts, with a duty cycle of ~18% and maximum pulse duration under 800 sec. The design is likely operated in C-class, although some cited Russian designs use A class or quasi-complementary AB-class circuits. If we then assume that each T/R channel can produce one kiloWatt of RF power with more powerful ganged RF transistors with a total rating of 500 Watt/~20% Duty Cycle, then this yields a rating of 2 x 12 x 1 kiloWatt for a total of 24 kiloWatts for a pair of arrays. The latter will require liquid cooling at any significant duty cycle. In comparison with X-band AESAs, these are excellent numbers, but for an L-band AESA with a factor of 10 or more lower antenna gain, are not necessarily stellar. The nett gain achievable by the each array element will depend strongly on the intended tradeoff between azimuthal angular coverage versus gain, but also upon the elevation coverage intended. For typical geometries of interest in air combat between combat aircraft, an elevation coverage of +5° to -15° would permit acquisition of most targets of interest, resulting in a mainlobe width in elevation of ~20°. From an antenna design perspective, narrowing the mainlobe in elevation is a modestly challenging task. Design options include changing the aspect ratio of the microstrip radiating element, or introducing a graded dielectric lens element in front of microstrip element, the latter approach used in existing Russian electronic warfare equipment for phased-array mainlobe shaping. Several estimations of element gain can be applied. The first is the simple rule of thumb estimate of ~6 dBi per element. If we assume a more refined design, with a mainlobe of 80° in azimuth and 40° in elevation, and apply Barton’s approximation, G = 30,000/( az x el), the element gain is ~9.7 dBi. Finally, we might assume a dielectric lens or more aggressive microstrip design, or some combination thereof, with an mainlobe size in elevation of 20°, which yields, again using Barton’s approximation, an element gain of ~13 dBi. Sidelobe performance will be poor compared to X-band AESAs, due to the limitations inherent in a 12 x 1 element linear array. While an aggressive taper function could be applied, the low element count precludes very low sidelobe performance, even with concurrent element gain and phase control. Receiver noise figure performance for the L-band AESA should be excellent, due to the short feed between the T/R module and antenna element, the potential for low-loss integral directional coupler design, and typical transistor noise figures in the L-band of a small fraction of a dB. The effective noise figure is likely to be dominated by losses between the antenna and transistor, and of the order of 1dB. Overall system noise temperature will be dominated by antenna noise produced by the environment. What choices in PRF, CPI, duty cycles and pulse compression technique Tikhomirov NIIP will opt for remains to be seen.
Little has been disclosed on existing X-band designs to date, although public disclosures suggest that Barker codes may be in use for pulse compression. Open source data indicates that most operating modes in Russian pulse-Doppler designs emulate those commonly used in US and European designs, with medium and high PRF modes commonly used. At least one Russian design is known to interleave medium PRF and high PRF regimes to maximise performance against concurrent mixes of closing and receding targets. Detection range performance in coherent pulse-Doppler designs depends strongly on power-aperture product, but also on coherent integration time, PRF, and duty cycle. f the intent of the design is to maximise detection range against closing low signature targets, then the design imperative will be to maximise the emitted energy per dwell, and minimise the noise bandwidth. This usually leads to the choice of a high PRF regime velocity search (VS) or tange gated high PRF range-while-search (RWS) regime, or some interleaved combination of the two, with a maximum coherent integration time duration to maximise the coherent integration gain. While X-band radars have high PRF regimes at 100kHz to 300kHz, an L-band design will exhibit similar unambiguous Doppler at much lower PRFs, of the order of 25kHz to 75kHz, due to the four to six times lower operating frequency. In the cardinal co-altitude air-to-air engagement geometry for closing high-speed targets at medium to high altitudes, the target Doppler will be well outside mainlobe clutter (MLC) and sidelobe clutter (SLC), which simplifies analysis. As the radar scans only in azimuth, the available dwell time per angle can be greater than in a comparable X-band search radar mode, thus minimising the dB loss incurred due to beamshape and scan considerations, another simplification to the model. A key consideration in such a regime of operation is that of how many pulses can be coherently integrated. This will be limited by the coherence length/time of the master oscillator employed, a parameter the Russians have not disclosed for any recent radar designs, and the Doppler filter bandwidth, which is readily estimated. Non-coherent integration incurs up to several dB of loss in the integration of large pulse trains.
Growth options include: increasing the power rating of the existing T/R modules while retaining conduction cooling; further increasing the power rating of the T/R modules and introducing liquid cooling; improvements to antenna element design to increase element gain; extending the arrays further along the wings to add an additional one or two sub-arrays; and the addition of receiver arrays in the leading edge of the vertical tails to provide dual-plane monopulse precision angle tracking capability for fire-control purposes.
For instance, increasing the array size to 16 elements improves power-aperture product for the existing design by almost 80%, by virtue of additional gain and transmit power. The practical limit will be the available leading edge flap volume as the design progressively tapers toward the wingtips, and system constrains on liquid cooling capacity.