The Magnetron
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| 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. |
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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
cavities…
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. |
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| From
the 1935 magazine: 'Electronics' |
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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.
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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.
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