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Can Eurofighter's radar win UK's biggest engineering prize?

July 03, 2000

BAE Systems Avionics Group, based in Edinburgh, has been shortlisted for this year's £50,000 Royal Academy of Engineering MacRobert Award, the UK's most coveted prize for engineering innovation, for the world's first airborne radar that can see all the targets all the time. The unique ECR-90 microwave radar was developed specially for Eurofighter, although it may well be applied to other aircraft in future. Professor John Roulston, Paul Holbourn, Tony Kinghorn, David Graham and Russell Shoulder have spent 10 years solving some of the most intractable problems in radar technology to come up with a world-beating design.

ECR-90 solves a fundamental problem experienced by all previous airborne radar systems - called the "look-down" problem, where the radar signal from the ground itself obscures that of any genuine airborne targets flying close to the ground. Previous approaches have had to compromise the interval of space or speed range in which targets were detectable in order to avoid this masking effect.

The team exploited Doppler shift to solve the problem, recognising that the radar echo from a moving target will have a frequency slightly different to that from a static target (ie. the ground). This is the same phenomenon that makes a siren appear to shift to a lower frequency as an ambulance approaches and then moves away from you. However, in the past the only way to measure Doppler shift out to a high enough frequency to cover all likely targets was to operate the radar at a high pulse repetition rate. This seriously compromises the ability to measure target range, causing confusion between near and far away targets.

The solution was to use a set of different medium pulse repetition rates and combine the measurements from them with some extremely complex mathematical processing in a protocol unique to BAE Systems. This forms the basis of the software and sets the precision and accuracy for the radar components. In effect the ground echo is controlled as much as possible and then systematically positioned, by controlling the pulse rate, to allow the target signal to shine through. ECR-90 is now the only airborne radar in the world that sees every target, whatever its position or speed. It measures target angle to within one milliradian and range to within 10 metres over hundreds of miles, even while flying supersonically or manoeuvring.

Added to the signal processing capability, ECR-90 is robust enough to cope with the flight conditions in one of the world's most advanced jets. It must continue to operate at full precision during 9g turns when its own weight of 200 kilograms effectively becomes around two tonnes. Despite its stressful environment, ECR-90 is designed for high reliability and low cost of ownership. It uses pioneering software to monitor its own performance to calibrate errors and diagnose components that need replacing - only NASA uses programming more sophisticated than this.

"The European consortium building Eurofighter has ordered 620 radars and as many orders again are expected for export," says Technical Director Professor John Roulston. "The earning capacity for the UK runs into billions of pounds - a sound investment from the £300 million development phase. ECR-90's technical achievements also have spin-off benefits in many other areas, from medical imaging to communications."

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Royal Academy of Engineering