Abstract:

The magnetron is a device for producing microwave energy at frequencies between 1 GHz and 300 GHz. Early magnetron designs, were investigated and patented by many groups in the late 1930’s. Pre-1939, these designs used glass envelopes to enclose the vacuum and they delivered generally only modest ~10 W power levels, well below kW values required to implement an airborne radar system.
The radical improvement in power was achieved by the Birmingham University researchers novel anode design, where the cavity resonator drilled from a solid block of copper to achieve more efficient cooling and permit much higher output power. In February 1940, their first laboratory device produced 400 W power at 10 cm wavelength.
In April 1940 the Government sponsors contracted GEC, Wembley, to extend this into a manufacturable device with neither a vacuum pump or electromagnet. Just before the fall of France, Maurice Ponte had brought to GEC their French magnetron device samples, incorporating an oxide-coated cylindrical cathode, achieving a much longer lifetime. Eric Megaw’s GEC redesigned magnetron, with a 6 lb permanent magnet and a thoriated-tungsten spiral cathode, then gave on 29 June 1940, an initial 3 kW output.
As Britain lacked the wartime manufacturing capability for the cavity magnetron, Winston Churchill agreed that Sir Henry Tizard should offer the magnetron design to the Americans to enable the parallel development of magnetron-based airborne radar systems in Britain and America. The Americans quickly established the Radiation Lab at MIT, close to Boston, which was second in size to the Manhattan project! High resolution microwave airborne radar, which provided accurate ground maps for bomb aiming and facilitated the detection and destruction of surfaced U-boats, relied on the fabrication of 250,000 cavity magnetrons during WW2.
Although these cavity magnetrons are today no longer used for radar, they are located in microwave ovens in a global market exceeding $12 billion p.a. sales, with 93% of UK households using a microwave oven. This demonstrates clearly the continuing impact of these wartime Birmingham innovations and subsequent GEC engineering advances.

Biography:

Peter M. Grant is a Life Fellow of IEEE. He was born in St. Andrews, Scotland and received his BSc from Heriot-Watt University in 1966 and his PhD from The University of Edinburgh in 1975, honorary DEng’s from Heriot-Watt in 2006 and Edinburgh Napier University in 2007, and, a further Honorary Doctorate from the University of Edinburgh in 2016.
He was appointed at The University of Edinburgh in 1971, subsequently promoted to a Full Professor before serving as the first Head of the School for Engineering, 2002-8. His research in signal processing for communication systems, was recognized with the 82nd (2004) Faraday Medal award by the Institution of Electrical Engineers. In 1998-9 he was appointed by the IEEE Signal Processing Society as a distinguished lecturer on DSP for Mobile Communications.
He was, in 2007, appointed to the 8th Regius Professor of Engineering at Edinburgh. In 2009 he was made an officer of the order of the British Empire (OBE) in the Queen’s Birthday Honours List. He holds fellowships of EURASIP, the Royal Academy of Engineering and the Royal Society of Edinburgh. He served for 14 years as a Trustee of the James Clerk Maxwell Foundation hosting museum visitors and provides public talks on life of Maxwell.