Aircraft interception radar
[4] The term was first used circa 1936, when a group at the Bawdsey Manor research center began considering how to fit a radar system into an aircraft.
VII, AI moved to microwave frequencies using the cavity magnetron, greatly improving performance while reducing size and weight.
This gave the UK an enormous lead over their counterparts in the Luftwaffe, an advantage that was to exist for the remainder of World War II.
In order to provide the maximum possible warning time of an incoming raid, the RAF's Chain Home (CH) radar stations had been positioned as far forward as possible, right on the coastline.
[5] Due to delays in the flow of information between the various centres, and inherent inaccuracies in the reports coming from multiple sources, this system was accurate to perhaps 5 miles (8.0 km).
Once the enemy aircraft passed the coastline they could not be seen by the radars, and the ROC could not see at night except under ideal conditions with bright moonlight, no cloud cover, and considerable luck.
Even when tracks could be developed, the difficulty of spotting a target from the cockpit of an aircraft while flying it at night proved to be equally difficult.
The first AI experiments thus used ground-based transmitters and a receiver fit to a Handley Page Heyford bomber, with an antenna consisting of a wire strung between the fixed landing gear.
[17] In February 1940, John Randall and Harry Boot at Birmingham University successfully ran the first cavity magnetron, eventually generating 1 kW at 9.8 cm (3,060 MHz).
While a team under Herbert Skinner developed the electronics, Bernard Lovell was put in charge of examining the use of a parabolic dish to improve the directionality of the signal.
The resulting beam was so sharply focussed, spanning about 10 degrees, that it easily avoided ground reflections at even low altitudes.
[21] First introduced in March 1941, it was found that the ground reflection created a sort of artificial horizon on the bottom of the display, a surprising side-effect which proved very useful.
[23] This run was followed by the production Mark VIII that included the new "strapped magnetron" of 25 kW, improving range to about 5.5 miles (8.9 km).
[25][26] "Freddie" Williams joined the effort,[b] and by the autumn of 1941 the system was basically functional and plans began to introduce it as the Mark IX.
Bomber Command had been pressing to use window over Germany to reduce their losses, which were beginning to mount as the German defensive network improved.
[28] A series of tests carried out in September 1942 by Wing Commander Derek Jackson suggested that some changes to the display systems might solve the problems with window on the Mk.
IX might ignore the window completely, as the light metal strips rapidly dispersed from the target being tracked, faster than the radar could follow.
With the night fighter force certain of its ability to continue operating successfully if needed, Bomber Command received clearance to begin using window on 16 July 1943.
X became one of the UK's most widely used fighter radars, largely because a lack of foreign exchange to purchase newer designs, and the poor economy in general which required the RAF to have a "make do" attitude.
[33] For the Fleet Air Arm, the TRE developed a series of AI radars operating at the even shorter 3 cm wavelength, the X band, which further reduced the size of the antennas.
It also included a switch that reduced the scanning pattern to a 15 degree cone in front of the aircraft, producing a C-scope view used during the final approach.
18 operated in the X band with a 180 kW peak power, using a 29 inches (740 mm) parabolic dish that could be pointed ±100° in azimuth, +50/-40° in elevation, and could keep a lock at as much as 75° in roll.
18 was able to detect the English Electric Canberra at 28 nautical miles (52 km) at altitudes over 20,000 feet (6,100 m) and a closing speed of 900 knots (1,700 km/h).
Testing started in 1955, and the AI.20 demonstrated its ability to lock-on to a Hawker Hunter sized target at 7 miles (11 km) 95% of the time, excellent performance for that era.
[44] The next year the MoS published a requirement for a new tail warning radar for the V bomber force, replacing the original Orange Putter, and quickly chose the AI.20 as its basis.
Work on F.155 ended with the infamous 1957 Defence White Paper, but by this time the interim English Electric Lightning design, the P.1, had progressed to the point where development was undertaken anyway (along with TSR.2).
The system was mounted entirely in a single bullet-shaped housing that was suspended within the Lightning's circular nose air intake.
[50] AI.23 was able to detect and track a Bear-sized bomber at 40 miles (64 km), allowing the Lightning to accomplish fully independent interceptions with only the minimum of ground assistance.
Development of the ADV began in 1976 and the radar system contract was eventually won by a curious combined bid; Marconi and Elliot Automation would provide most of the design, while Ferranti built the transmitter section and Antenna Platform.
[55] Foxhunter finally entered service in the late 1980s and early 1990s, by which time the older Skyflash missiles were in the process of being replaced by the new AMRAAM.
