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Trends in combat jet sensors of relevance to the Indian Air Force's transformation

Saurav Jha @SJha1618

Updated: July 19, 2014, 1:18 PM IST
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In 2007 during the run up to the medium multirole combat aircraft (MMRCA) decision, the then air chief had remarked that what matters today is not the exterior of the aircraft but what is inside it. This was of course an allusion to the centrality that combat jet tactical avionics has in determining the efficacy of the same. Indeed it is primarily for this reason that 40-60 percent of the cost of a modern fighter can be attributed to the on board tactical avionics package and associated software. As the Indian air force (IAF) transforms itself over this decade it would be worthwhile to look at the transition it is making in terms of combat sensors through potential new inductions and upgrades.

The term avionics was coined by journalist Philip J Klass who condensed 'aviation electronics' to arrive at it. Modern on board avionics as such includes all primary sensors, electronic warfare systems, cockpit instrumentation and the mission computer carried by a combat jet. The coming together of these packages turns the modern combat jet into a flying platform that senses as well as shoots. Now the chief sensor on board any modern combat jet is the fighter radar which today has to be competent in both air to air as well as air to ground modes. Worldwide, the shift in fighter radar technology has been towards active electronically scanned arrays (AESAs) and this was also a major consideration in the MMRCA tender as indicated by various sources. Indeed, the winner of that tender i.e the Dassault Rafale passed an important milestone last October when the first RBE2-AA AESA equipped Rafale (numbered C137) was delivered to the French Airforce. The RBE2 -AA is an AESA upgrade of the staple passive array (PESA) RBE2 and affords a significant improvement over it in terms of low probability of intercept (LPI) features. Typically, AESA receivers are at least 6 decibels (db) quieter than comparable PESAs.

Interestingly the RBE2-AA employs a "single channel" approach where each element in an AESA's transmit/ receive (t/r) module employs a stack of components perpendicular to the antenna face. This new packaging scheme seeks to overcome limits on t/r density and helps lower cooling requirements both of which otherwise put an upper bound on the power-aperture performance of AESAs. The contemporary power density benchmark for an AESA is around 5 watts per centimetre at the array face and to achieve this a single channel or element in an AESA consists of an LNA for the receive path, a power amplifier, a phase shifter, impedance matched low insertion loss interconnections, gain control blocks, radio frequency buffer amplifiers, digital circuits alongside the control logic required to latch downloaded gain and phase parameters into the t/r module phase shifter and gain control components.

The IAF of course is extremely keen on equipping more of its combat jets with AESAs. Several of the IAF's Sukhoi 30 MKIs (Su-30 MKIs) are soon going to be due for a mid-life upgrade (MLU) which will include the replacement of the very capable but now ageing Bars PESA with a new Russian origin AESA. It could be speculated that this might be the same AESA radar as the Tikhomirov NIIP design which is intended for the Indo-Russian FGFA based on the Sukhoi T-50 PAK-FA.

The Tikhomirov NIIP X-band AESA design for the PAK-FA was extensively displayed by Tikhomirov NIIP at MAKS 2009. The antenna aperture is similar in size to the aperture of the N-011M Irbis E used in the Su-35S. The design has some 1,526 t/r channels, with a tolerance level of perhaps several percent. NIIP has publicly cited a detection range performance of 350 to 400 km while assuming a 2.5 RCS target, and peak power may be in the order of 15 kilowatts.

An indigenous AESA is also being pursued by DRDO's electronics research and development establishment (LRDE) and centre for airborne systems (CABS) under Project Uttam which is looking at new generation X-band AESAs which incorporate improvements in monolithic device technology by moving from the use of Gallium Arsenide based monolithic microwave integrated circuits (MMiC) to those built from Gallium Nitride and Silicon Germanium. Given that this project looks to provide a fighter AESA for the LCA Mk-2, the project has to deal with unique packaging and power requirement challenges. One of the strategies to deal with the same is apparently the use of MEMS based phase shifters in this program.

In an age of stealth however, radars are no longer the only kind of sensor that find pride of place in a combat jet's tracking and scanning systems. Fighter aircraft today sport increasingly capable electro-optical tracking systems that are merging together the functions of the TV telescope, infrared search and track (IRS&T) and forward looking infrared (FLIR) into a single device. The technological enabler for this synthesis is the emergence of the Indium Antimonide single chip Focal Plane Array (FPA) camera. This camera type can be used for passive IRS&T searches, as well as to 'stare' at a specific target for beyond visual range (BVR) identification and targeting.

One sees this merger in the optronique secteur frontal (OSD) long range video system of the Dassault Rafale. The narrow field of this sensor coupled with visible waveband capability enables the identification of targets in situations where visual contact is required by the rules of engagement. The OSD also allows target tracking, through both the IRS&T as well as visual sensors and the FLIR function can apparently be used to detect air targets at ranges up to 100 kms away.

However, it is the Russians who seem to take these devices most seriously as evidenced by the continuing development of the (optical laser system) OLS-35 for the Sukhoi family. The OLS-35 is quite versatile and can accomplish the following tasks according to the manufacturer-

- Airspace scanning in air-to-air mode

- Aerial, ground and water surface target detection, locking-on and tracking

- Ground surface scanning

- Target image recognition

- Target angular coordinates, range and angular and linear velocity determination

- TV, IR and TV+IR video and message output to the cockpt multifunctional display

- Interaction with the aircraft targeting and guidance comple

- Operation at a full range of altitudes, ground and sky backgrounds, day and night, in different visual meteorological conditions and jamming interference

- Ground target illumination by laser emission

- Autonomous functioning and radio silence mode

Despite the capabilities mentioned above, the contemporary fighter's radar or optical sensor on their own may not give the pilot a complete air situation picture. For that a dovetailing of inputs from all on board sensors for greater situational awareness otherwise known as sensor fusion proves useful. AESAs in any case are software intensive with rigid real-time processing demands requiring the refinement of the computing architecture of modern fighter aircraft.

Indeed data management for fighter aircraft today is inconceivable without the availability of serious on board processing and man-machine interface facilities in the form of a state of the art mission computer and a digital 'glass' cockpit providing the necessary inputs to the pilot in a readily available manner. The mission computer and a digital cockpit after all are responsible for not just sensor input management but for flying the aircraft and deploying its weapons. This is also why the adoption of integrated modular avionics (IMA) that encapsulate real-time approaches to onboard data processing orchestrated by a network made of distinct computing modules capable of supporting numerous applications of differing priority levels is now being pursued. Sequenced and prioritized information in IMA environments when fed to glass cockpit consisting of large side by side AMLCD multi-functional displays, wide angle colour head up displays, HOTAS controls and new generation helmet mounted cueing systems represent no less of a generational jump then the appearance of true very low observable(VLO) systems.

However the situational awareness for a fighter can never be complete without the ability to detect and neutralize threats to itself. Given that anti-aircraft technologies have not stagnated either, there is an increasing move towards developing integrated electronic warfare (EW) suites for fighters. For example the Rafale's SPECTRA (Self-Protection Equipment Countering Threats to Rafale Aircraft) suite developed by Thales combines long-range detection, identification and accurate localisation of infrared, electromagnetic and laser threats. SPECTRA incorporates radar warning, laser warning and missile warning receivers for threat detection in addition to a phased array radar jammer and a decoy dispenser for threat countering. It also has a dedicated management unit for data fusion and reaction decision.

SPECTRA is of course part of a larger worldwide movement towards integrated EW and even the indigenous LCA project has notched up a fair degree of success in the development of such systems by DRDO's Defence Avionics Research Establishment (DARE). DARE has also helped indigenize a lot of the avionics in the Su-30 MKI through Project Vetrivale. In fact, the success of Project Vetrivale has actually created a situation whereby domestic Indian companies such as SAMTEL are emerging as major suppliers of not just avionics components but systems itself as symbolized by the indigenous 'Divya Dhristi' helmet mounted display. In the future, the avionics sector in India is likely to witness the most significant growth among all aerospace segments not in the least due to the IAF's continuing transformation.
First Published: July 19, 2014, 1:18 PM IST

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