These were powerful S-band radars able to detect high-flying bombers at ranges as great as 250 miles (400 km).
However, due to the curvature of the Earth, they were subject to the local radar horizon so low-flying aircraft were not visible until they approached much more closely.
A system using two barrage balloons developed by the Royal Aircraft Establishment (RAE) at RAF Cardington was eventually selected.
This system tapped into the changing voltage being sent to the radar display, the video signal, and sent it to the reflector plate of a reflex klystron.
[2] After discussing the concept in 1953 with several manufacturers, in 1954 a contract was signed with Metropolitan-Vickers to develop the system under the rainbow code "Blue Joker".
The radar was a fairly conventional model for the era, using a cavity magnetron as the transmitter source and a reflex klystron as a local oscillator in the superheterodyne receiver.
During trials the radar successfully tracked an approaching Canberra jet bomber, 120 miles away (190 km)[2] Wind proved to be a major problem for the system, limiting the safe flying speed to 70 knots (130 km/h; 81 mph), but only 30 knots (56 km/h; 35 mph) for handling on the ground.
The carcinotron can tune its microwave output over a very wide band, allowing it to match the frequency of any conventional radar system and effectively jam it.
[5] The 1957 Defence White Paper suggested that by the mid-1960s an air attack by manned bombers would be unlikely in a battle dominated by ballistic missiles.
It was of asbestos-fibre-reinforced phenolic resin with aluminium stripes glued to the front to act as the reflector surface.
This was accomplished by mounting it inside a large gyroscopically leveled gimbal system with the antenna on one side and the electronics on the other to balance it out.
The pole also acted as the connection points on the top and bottom for the guy wires that ran to the ground below and the balloons above.