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The Cavity Magnetron

Radar (Radio Detection and Ranging) was first developed in Britain in the 1930s. This online exhibition looks at the scientists and engineers behind the development of radar during World War Two.

The early Chain Home radar system was based on wavelengths of 15 to 30 metres. It was obvious that if shorter wavelengths (i.e. below 1 metre) could be used then radar could be far more effective.

In 1939, a team was set up under Professor Mark Oliphant to attempt to develop a generator capable of producing radio waves at a wavelength of approximately 10cm. This team included H A H (Harry) Boot and J T Randall, who were allocated the magnetron for development.

Photograph of an air cooled magnetron
Cavity Magnetron

It was Randall who came up with the idea of using cavity resonant circuits inside the magnetron to produce radio waves of the desired frequency. Boot took Randall's design and demonstrated that, by connecting the magnetron to a Lecher wire system, wavelengths of 9.8 cm could be produced. The cavity magnetron was born.

The IET Archives hold Harry Boot's notebooks in which he describes the possibility of increasing the magnetron's efficiency.

Read more in the Henry Boot biography and the Featured Article: GEC Wembley Laboratories and the Cavity Magnetron.

Next page → Magnetron Development

Back to Radar Exhibition