AI.20 radar

AI.20
Country of originUK
ManufacturerEKCO
Introduced1955 (testing)
FrequencyX band
RPM1,000
Range25 mi (40 km)
Diameter18 in (460 mm)
Azimuth45º
Power200 kW
Other NamesGreen Willow
RelatedRed Steer

Radar, Aircraft Interception, Mark 20, or AI.20 for short, also known by its rainbow codename Green Willow, was a prototype aircraft interception (AI) radar developed by EKCO for the English Electric Lightning interceptor aircraft. It was ordered as a backup system in case the more advanced AIRPASS radar from Ferranti failed to develop, but when AIRPASS entered testing in 1955, AI.20 was dropped. The system was used, almost unchanged, as the basis for the Red Steer tail warning radar used in the Handley Page Victor and Avro Vulcan strategic bombers.