In today’s air warfare, the Airborne Early Warning and Control (AEW&C) aircraft will detect, identify and classify hostile intruders and then, acting as a Command & Control Centre, will employ its air defence forces to neutralize the threats to Nation’s assets.

AN ‘EYE’ IN THE SKY

The significant inventions of the early 20th century, viz., the aircraft and the RADAR, led to the clever combination of the two technologies giving birth to a distinctly identified ‘Air-borne Early Warning and Control’ (AEW&C) concept, thus re-writing the tactics for today’s air-warfare.

The roles that the two dominant AEW&C systems, viz., the E-2C Hawkeye and the E-3 AWACS played during the Gulf War (1991) amply illustrate the power of these systems. During Operation Desert Shield and Desert Storm, the AEW&C aircraft helped overcome surveillance deficiencies and conduct successful air operations. They assisted the fighter fleet by providing early threat detection and building up situational awareness that led to 39 out of 41 air-to-air engagements being successful.

The AEW&C system soon proved itself to be a dominant Force Multiplier with its abilities to execute multiple functions - Surveillance, Early Warning, Electronic Intelligence, Communication Intel l igence, Command and Control tasks, Battle Management, etc. – all from a single airborne platform. The AEW&C systems effectively impacted the dynamics of air warfare and irreversibly changed its nature.

ELECTRONICALLY STEERED ARRAY RADAR

Both E-2C Hawkeye and E-3 AWACS aircraft carried mechanically steered antenna (MSA) in a rotating dome to scan the sky. In the early 1990s, a more versatile breed of AEW&C systems with Electronically Steered Array radar started making their appearance progressively.

The AESA is mounted in a fixed position on the aircraft structure and the beam is steered by individually controlling the phase of the radio waves transmitted and received by each of the multiple radiating elements in the antenna.

The inherent advantages of the AESA radar are the obvious ‘inertia less scanning’ and the ‘minimal feeder loss’ as no lengthy feeder cables are involved. Unlike in the Mechanically Scanned Array (MSA) Radar, the AESA Radar has the impudence to perform even with failure of some of its radiating elements. The AESA radar goes through a graceful degradation with cumulative failures in its battery of Transmit-Receive modules. The AESA Radar helps build substantially more compact radar systems resulting in low weight, minimal aerodynamic drag and relatively smaller Radar Cross Section (RCS), all of which are operationally of vital importance for the platform aircraft. Besides, the AESA radar provides enhanced beam agility with higher reliability. The latest AESA sensor further helps track air- and sea- targets simultaneously as well as tracks continuously the high-performance aircraft, while maintaining the routine scan over the operational area.

SAAB-340 AEW&C

The world’s first of the AEW&C systems to sport AESA radar was the Swedish Saab-340 AEW&C aircraft. The Saab-340 is a twin-engine turboprop aircraft. An AEW version with phased-array radar, Erieye, in a rectangular pod on top of the fuselage was delivered in 1994. The Swedish Air Force ordered for six units of the aircraft. Some numbers are used by Japan as Search-and- Rescue aircraft. A recent variant of Saab-340 AEW&C, designated Saab-2000 AEW&C, using the same Erieye AESA radar, has been ordered by Pakistan.

The Ericsson Erieye radar uses an active array with 200 solid state modules. The antenna is housed in a 9m long box radome mounted atop thet fuselage. The look angle on each side of the radome is about 120 degrees in the azimuth. Since the surveillance is on the sides, azimuth coverage of 120 degrees is not a limitation and the practice has been there for over a decade.

The electronically scanned antenna can scan sectors of interest frequently while others are monitored; and a single sector can be scanned in different modes at the same time. The aircraft functions as an airborne radar integrated with the total air defence network.

EMB-145 AEW&C

Brazil saw the virtue of the Ericsson Erieye radar of the Saab-340 AEW&C and chose to mount the same on its bigger and faster twin-engine regional jet aircraft, EMB-145. The endurance of this system is about six hours.

M/s Embraer of Brazil built the EMB-145 AEW&C aircraft for Air Forces of Brazil, Mexico and Greece with the Erieye radar and other subsystems as opted by the user Air Forces. These subsystems include radar, Identification Friend or Foe, Communication Support Measures, Electronic Support Measures, and Data/Voice Communications.

G-550 CAEW

In the year 2001, M/s ELTA of Israel started work on a Conformal Airborne Early Warning aircraft based on the Gulfstream G-550. This system, called the G-550 CAEW, includes phased array radar, phased array IFF, Signal Intelligence (SIGINT), and a communications system. The communications system includes a data-link and satellite communication (SATCOM) system for secure high-speed connectivity with ground stations. The ELTA radar conformally built on the sides of the fuselage works on the ‘L’-Band and provides coverage on the LH and RH sides. In the forward and aft directions, independent radars mounted on the nose and tail of the aircraft work on the ‘S’-Band and provide radar coverage of relatively reduced range. Consequently, total azimuth coverage is effectively only for 240 degrees and the rest of the azimuth coverage is limited in range. The G-550 CAEW is now ready and on order for Israel and Singapore.

The endurance of this system is about eight hours.

B-737 AEW&C, WEDGETAIL

The Boeing Company is building for the Royal Australian Air Force (RAAF) an AEW&C system designated B-737 AEW&C, Wedgetail. The Boeing AEW&C Solution combines the new Boeing 737-700 aircraft with the Northrop Grumman Multirole Electronically Scanned Array (MESA) radar. Included in the platform are an Identification Friend or Foe (IFF) system; an expanded, passive electronic surveillance system; and an effective selfdefence capability.

Northrop Grumman’s MESA radar is mounted in a rectangular ‘T’- structure atop the fuselage providing for 240-degrees full range coverage and for the rest of the azimuth angle partial range coverage. The cabin houses six Mission Operator Consoles. The radar can track air and sea targets simultaneously and can help the operator track high-performance aircraft while continuously scanning the operational area. The endurance of this system is about eight hours.

The 737 AEW&C platform, with its interoperability with the E-3 and B-767 AWACS aircraft, is designed to fill the airborne-surveillance needs of Australia. The first of the six planes ordered by the RAAF is due to be delivered in 2010. Turkey has also ordered for a few numbers of the B-737 AEW&C.

IL-76 AWACS

Israel and Russia are jointly developing an AWACS system for Indian Air Force with true 360° azimuth coverage radar built into the Russian Briev IL-76 aircraft platform. This system is built around an AESA ‘L’-band radar, and adds electronic and communications intelligence gathering (ELINT and COMINT) capabilities. The system is interoperable with other air and ground stations, and uses sensor fusion to provide a complete picture of the battle space.

India’s IL-76 AWACS will use a conventional circular radome mounted on top of its fuselage. The radome will, however, be fixed and not rotating. The ELTA radar, with a set of three phased-arrays housed in a triangular configuration inside the radome, will operate in ‘L’-Band and scan 360 degrees in the azimuth. The endurance of this system is about seven hours.

Delivery of the first IL-76 AWACS system to Indian Air Force is slated to be in mid 2009 and completed by the year 2011.

THE INDIGENOUS AEW&C SYSTEM

The Defence Research and Development Organisation (DRDO) have launched an Indigenous AEW&C programme that is focussed on specific needs of the Indian Air Force. The Centre for Air-Borne Systems (CABS) of the DRDO is tasked with the development of the system and the centre is pursuing the programme with participation of multiple workcentres from within DRDO as well as Indian industries in the Public and Private Sector.

The Indian AEW&C system is at par in respect of functionalities with any of the modern AWACS/AEW&C systems in the world.

The Indian AEW&C system to be integrated on to an Embraer EMB- 145 Regional Jet class of aircraft will detect, identify and classify threats present in the surveillance area and act as a Command and Control Centre to support Air Defence operations. The system with its multiple Communication and Data Links can alert and direct fighters against threats while providing ‘Recognizable Air Situation Picture’ to commanders at the Ground Exploitation Stations that are strategically located. The AEW&C system can thus support Air Force in offensive strike missions and assist Forces in the tactical battle area. Besides, the Electronic and Communication Support Measures of the system can intercept and counter unfriendly radar transmissions and communication signals.

The primary sensor for the AEW&C will be the indigenous AESA “S”-Band radar with adequate detection range against targets of the fighter class of aircraft. Two radiating planar arrays assembled back-to-back and mounted on top of the fuselage in an Active Antenna Array Unit (AAAU) will provide nearly 150° coverage on either side of the AAAU. The important modes of operation of the system are the surface surveillance and the air surveillance.

The sensor has the abilities to search, track while scan, priority tracking, high performance tracking, etc. In priority tracking, the targets will be placed in full track mode even if they cross the primary surveillance area. In high performance tracking, additional measurements will be made to improve the tracking accuracies. Utilising the active aperture technology, the radar provides a fastbeam agile system that can operate in several modes concurrently. Interoperability with AWACS, other AEW&C aircraft, fighters and Ground Exploitation Stations is ensured using data-links with voice and data channels.

The endurance of nine hours with one Air-to-Air Refuelling.

The aircraft cabin houses five Operator Work Stations to adequately meet requirements of the operational mission tasks. An Air-to-Air Refuelling system enables extended operations at times of need. The system is expected to be available in 2012.

CONCLUSION

It is evident that most of the modern AWACS/AEW&C systems using Active Electronically Steered Array Radar are yet to be in the market with the exception of Saab-340/EMB-145 with Ericsson’s Erieye radar. The total cost of an AWACS/AEW&C system is determined by the Procurement Cost and the Life-cycle Cost. The Indian AEW&C system will have, for known reasons, a price advantage in the international market.

Considerable thought has gone into arriving at the configuration design of the Indigenous EMB- 145 AEW&C system to make the EMB-145 platform aircraft and the AEW&C Mission System a win-win combination to realise a compact and optimal surveillance system that meets the Air Force’s requirements fully and cost-effectively. When the EMB-145 AEW&C India takes to the air in 2012, it will be one among the select breed of Watchdogs of the Skies.

Dr S Christopher is Director, Centre for Air-borne Systems, Defence Research & Development Organisation, Bangalore.