What wavelength did early radars use, and why wouldn't it…

What wavelength did early radars use, and why wouldn't it fit on a plane?

Short answer

The 10 cm wavelength radar only became reality in 1940, when John Randall and Harry Boot developed the cavity magnetron. Before that, the Chain Home stations held their transmitting antennas on 110 m (360 ft) steel towers. The compact magnetron shrank radar equipment so much that it could easily be installed in aircraft.

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

What wavelength did early radars use, and why wouldn't it fit on a plane?

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

Antennas held up by towers

At the first stations, four 360 ft (110 m) steel towers supported the transmitting antennas, and another four 240 ft (73 m) wooden towers supported arrays of crossed dipoles.

The cavity magnetron

In 1940, John Randall and Harry Boot developed the cavity magnetron, which made ten-centimetre-wavelength radar a reality. Their first working example delivered hundreds of watts at a wavelength of 10 cm, an unprecedented achievement. The 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. Within weeks, GEC engineers had raised the power well above one kilowatt; within months, to 25 kW; above 100 kW in 1941; and on the way to a megawatt in 1943. The compact cavity magnetron drastically reduced the size of radar equipment, so that it could be installed more easily in night fighters, anti-submarine aircraft and escort ships.

From the laboratory to the aircraft

By early 1941, portable centimetric radars were already being tested in American and British aircraft. The unpressurised rotodome of the Boeing E-3 Sentry measures 9.1 m (30 ft) in diameter and 1.8 m (6 ft) thick at its centre, and is held 3.4 m (11 ft) above the fuselage by two struts. In 1963 the USAF requested proposals for an airborne warning and control system (AWACS) to replace its EC-121 Warning Stars, which had been in the airborne early-warning role for more than a decade.