Radar Recollections - A Bournemouth University / CHiDE / HLF project


The Magnetron

Operating wavelengths were dropping steadily during the period 1935 - 1940 and each new improvement in design required a more powerful transmitter and a more sensitive receiver. The lower limit to this process seemed to be at about 1.5m wavelengths. Airborne and shipborne radar in particular needed very short wavelengths to negate the massive ground reflection echoes produced by longer wave systems. Mathematically, 10 cm was thought to be ideal.
A Laboratory Magnetron
In December 1939, contracts were placed with Professor Oliphant's laboratory at Birmingham University to develop valves that could deliver enough power to drive a 10cm system. John Randall and Harry Boot, two young physicists were assigned to the task. Within 2 months (21st February 1940) they had produced a new kind of magnetron, one with 8 concentric
Randall got the inspirational idea of using 8 cavities when he researched the design of the original Hertz oscillator which was an open single ring. Randall saw that this structure could be extrapolated into a cylinder and then into 8 resonating chambers.
From the 1935 magazine: 'Electronics'

Microwaves To Detect Aircraft

In 1935, the Telefunken Company of Berlin was researching this device…, which may be the origin of the 'mystery ray' that Watson Watt later refers to.

A page from the 1935 magazine: 'Electronics'

The split anode magnetron had first been developed in 1921 by DR A.E.Hull of GEC in America.
Also in 1921, Haben, working in Germany, developed a similar device that worked on a 3 cm wavelength.

Dr H.E.Hollman registered many patents (between 1925 - 1935) that relate to magnetron development.

W. E. Burcham