FLUG REVUE February 2004: New radars for the latest fighters

NEW RADARS FOR FUTURE FIGHTERS

By Karl Schwarz

Over the last fifty years, radar has established itself as the single most important sensor on a fighter aircraft. Moreover, it appears unlikely that any other competing system will challenge it in the foreseeable future. Its fundamental advantages such as long range and all-weather and multi-mode (air-to-air and air-to-ground) capabilities are critical even in an age when, thanks to measures aimed at reducing the radar cross-section (Stealth technology), targets are becoming more and more difficult to detect.

Continuing development work has resulted in fire control radars which operate at the limits of what is physically feasible. The Captor radar (formerly known as the ECR90) installed on the Eurofighter is undoubtedly one of the best “conventional” systems with a mechanically steered antenna. The Euroradar consortium, consisting of BAE Systems (formerly Ferranti, then GEC-Marconi), EADS (formerly Telefunken Systemtechnik/DASA), Galileo Avionica (formerly FIAR) and Indra (formerly Inisel), has been working on its development and production since May 1990.

Captor radar

The Captor has the typical design of a latest generation pulse Doppler radar, on which all the parts are optimised for maximum performance combined with high reliability (well over 100 flying hours between failures, equivalent to one failure per year in normal flight operations).

Right at the front, as usual, is the flat slotted array antenna, built with enormous precision by EADS in Ulm. It is particularly light and is slewed extremely rapidly by powerful electric motors.

A waveguide unit carries the transmitter pulses to the antenna and the received signals to the receiver. This component also comes from EADS in Germany.

The radar signals are generated with a transmitter equipped with a powerful travelling wave tube (Galileo Avionica).

The reflected signals are evaluated in the receiver. BAE Systems is leading in this area, but some important components also come from Ulm.

A computer manages the radar and processes the data for display in the cockpit. Once again, this is a joint effort by BAE and EADS.

Finally there is another “black box” for the power supply, developed by Galileo Avionica.

The Captor's six line replaceable items (LRIs) contain a total of 61 shop replaceable items (SRIs). These will be maintained by the manufacturers under an industrial exchange and repair service for an initial term of three-and-a-half years. To maintain readiness, industry will hold spare parts at the operational bases.

While manufacture of the first series of Captor is running according to schedule (as of November 2003, LRIs for 82 systems had been delivered), the developers have already turned their attention towards the enhancements for Tranche 2. Apart from enhancement of the software and possible implementation of an operational mode for high-resolution radar maps, the top priority will to replace the computer. Its chips stopped being manufactured some time ago and must therefore be exchanged for the latest commercially available G4 AltiVec PowerPC processors.

Moreover, given the phenomenal rate of advances in computer technology, it is unlikely that this will be the only instance of computer obsolescence encountered during the lifetime of Captor. To contain the problem more effectively, the computer is to have a new architecture, and this time the software will be written in such a way that it still works with future generations of processor. Another step is to decouple the operating system from the operational programmes (radar operating modes etc). This design required extensive predevelopment work under the Allied Standard Avionics Architecture Council (ASAAC) programme, in which Germany, the United Kingdom and France have invested around Euro 60 million over a period of five years.

The exact form that Captor will take in the third Eurofighter tranche (for delivery from 2010) has not yet been determined. At any rate, the installation of an antenna with active electronic beam scanning is one possibility. Active electronically scanned arrays (AESAs) are becoming the norm in the design of radars for fighter aircraft and will make their debut in the USA on the F/A-22 Raptor, the improved F/A-18E/F Super Hornet, the F-16E/F Block 60 and, of course, the F-35.

Research in this direction is also under way in Europe. The GTDAR consortium (BAE Systems, EADS and Thales) has been working on an Airborne Multi-Role Solid State Active Array Radar (AMSAR) since 1994. Phase 2B, worth Euro 60 million, the go-ahead for which was given on 10 February 2003, will cover antenna and systems integration, ground and flight testing and multi-channel signal processing and will run through to 2008. Testing of the first antenna is to commence at the end of 2004.

AESA radars are designed quite differently from their predecessors. Instead of a single transmitter and receiver, typically they have over 1,000 small transmit/receive (T/R) modules. The only additional components are a computer and a power supply. Because there are no longer any moving parts, reliability is higher. Notoriously vulnerable components such as the travelling wave tube, with peak voltages of tens of thousands of volts, are no longer required. Even if individual T/R modules fail, up to a point this is not a problem, as 50 modules could fail and still the power would drop by less than five percent.

Of course there are also disadvantages, such as the restricted field of view of between 120 and 140 degrees of the fixed antenna. Moreover, steering of the beam would result in a significant reduction in power, since the effective antenna area (aperture) decreases as the off-boresight angle is increased. Another problem is the build-up of heat in the densely packed T/R modules, which requires liquid cooling.

But all in all the advantages of an AESA radar are alluring, especially the phenomenally fast agility of the radar beam. It can alter its direction of transmission in a matter of milliseconds, whereas mechanical steering operations take a second or more. This means that irregular (and hence difficult to detect) search patterns are not a problem. Searching in one sector while simultaneously tracking a target in a different direction presents little difficulty, nor does the handling of simultaneous air-to-air and air-to-ground tasks (the creation of radar maps, terrain following flight etc.).

With skilful management, the use of time and radar energy can be optimised. Targets detected are tracked more intensely, i.e. they are illuminated more frequently. Once a target has been identified, more energy is concentrated on it and for longer. Steering of individual blocks of T/R modules makes it possible to shape the lobes of the beam pattern in a highly flexible way and, for example, to position the “null” in such a way that jammers have little prospect of success. The simultaneous generation of several radar beams is also conceivable, while another possibility would be to transmit a very broad beam and then to split the returning signals into multiple, independent, narrow receive beams.

In this way, an AESA radar opens up a whole range of new possibilities. Development is still in its infancy. Miniaturisation of the T/R modules is like to boost further advances – shrinking them down to one-quarter of their present size appears to be feasible. Another possibility under consideration is modules in which the electronics are stacked on top of each other in several layers. These would be a lot shorter than present systems and could be placed in multiple positions on the aircraft so as to achieve extended radar coverage.

From page 72 of FLUG REVUE 2/2004

Last updated 10 January 2004

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