In 1940, early in the Second World War, Britain was hard-pressed dealing with its immediate defence.
Its engineers and scientists had come up with a number of inventions that could drastically affect the war effort, but there were few resources available to deploy them. After some discussions with Canada and America, Britain agreed to send these inventions and new technologies across the Atlantic for development here. One of the most important of these was the resonant cavity magnetron. This device, looking like a hockey puck with cooling fins, was the solution to a serious problem, how to generate huge amounts of power at centimetre wavelengths – microwaves.
There was a need for effective radars that would fit on planes, which meant small antennas, and radars that could detect submarine periscopes and even shells and bombs in flight. The problem was that such things needed radars that used microwaves, and there was no way of generating enough microwave power. Then the magnetron came along. Magnetrons were flown across the Atlantic and given to the National Research Council in Ottawa, and to the USA. One of these is now in the National Museum for Science and Technology in Ottawa. The NRC soon became a centre for front-line radar development for the allied war effort, producing new types of radar for applications on the ground, in the air and at sea.
Radar works by sending out pulses of radio waves. These pulses are reflected by aircraft, ships or anything else they encounter. By measuring the time between the pulse leaving the transmitter and when the echo arrives back, we can find the range of the target, and by measuring the direction that echo is coming from we can determine where that target is. This has led to designers making their aircraft and ships stealthy, that is, reflecting as little radar energy as possible. To counter the stealth approach, we can increase the power of the radar transmitter, to “paint” the target more heavily, which magnetrons make possible. We can also make the radar receiver as sensitive as possible, to detect really weak echoes. These receiver improvements powered Canada’s beginnings in radio astronomy.
During the war radars on the ground and on ships had produced a number of non-military discoveries. Antiaircraft radars detected radio emissions from solar flares, and radars on ships found that at sunrise and sunset, strong signals were detected when the radar antenna scanned across the Sun. Radars looking for V2 rockets detected meteors. Radar methods for studying meteors were used after the war in Canada, the UK and other countries.
After the war was over, radar development at NRC slowed down, and the engineers and scientists had time to think of other things. One result of this was the idea of using the receiver portion of a radar system to make Canada’s first radio telescope. This instrument was used for radio observations of the Sun and searching for other cosmic sources of radio emission. The limitations of using ex-military radar hardware for astronomy led Canada to invest in radio telescopes designed from the ground up for doing astronomy. Two radio observatories were established: the Dominion Radio Astrophysical Observatory in the Okanagan, BC, and the Algonquin Radio Observatory in Ontario. Today our involvement in radio astronomy comprises developing new instruments in Canada and also in international collaborations.
In addition to military uses, the magnetron went on to find applications in radars on airliners, merchant ships, and even small boats. However, today the most magnetrons are employed in kitchens and lunchrooms, heating food, as the key component in microwave ovens.
Jupiter is in the southeastern sky after sunset; Mars and Saturn rise around midnight. The Moon will be New on the 7th.
Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astrophysical Observatory, Penticton