Why did the British magnetron change radar?

Short answer

Because the cavity magnetron that John Randall and Harry Boot presented at the University of Birmingham in 1940 generated pulses of hundreds of watts at a 10 cm wavelength from a device the size of a small book, which cut radar size by orders of magnitude.

Published: November 4, 2026 · Updated: November 4, 2026 · Edited by Above Ten Thousand · Editorial policy

Why did the British magnetron change radar?

NATO E3A AWACS Paine Field WA Jul15 DSC8405This Photo was taken by Timothy A. Gonsalves. Feel free to use my photos, but please mention me as the author. I would much appreciate if you send me an email tagooty@yahoo.com or write on my talk page, for my information. Please contact me before commercial use. Please do not upload an edited image here without consulting me. I would like to make corrections only at my own source to ensure that the changes improve the image and are preserved.Otherwise you may upload an edited image with a new name. Please use one of the templates derivative or extract. (CC BY SA), vía commons

Before: antennas measured in metres

The British airborne radar line, led by E. G. Bowen, focused on 200 MHz (1.5 m) equipment, because the higher frequency allowed smaller antennas, suitable for fitting in aircraft. In 1937, Bowen's team used their rudimentary ASV radar, the world's first airborne set, to detect the Home Fleet in very bad weather.

The leap to centimetric waves

The cavity magnetron introduced by John Randall and Harry Boot at the University of Birmingham, England, in 1940 was a leap forward from earlier versions. Its first working example produced hundreds of watts at a 10 cm wavelength, an unprecedented achievement. Those high-power pulses came out of a device the size of a small book and were transmitted from an antenna only a few centimetres across, which cut the size of practical radars by orders of magnitude and allowed them to be fitted to fighters. Centimetric radar, which the cavity magnetron made possible, allowed much smaller objects to be detected and much smaller antennas to be used.

Radar carried aboard aircraft

In February 1944, the US Navy commissioned the development of a radar system that could be carried aloft aboard an aircraft, under Project Cadillac. An airborne early warning and control (AEW&C) aircraft flying at 9,000 m (30,000 ft) can cover an area of 312,000 km² (120,000 square miles).