Radar times radio echoes to map distance and speed
Radar systems transmit radio or microwave pulses and read returning echoes to find range, angles, and radial velocity. A transmitter, antennas, and receiver—often sharing one dish—turn reflections into tracks for planes, weather, and more. Britain's Chain Home stations used it to watch the skies before the Second World War.
Radar uses radio waves to find how far away an object is, in which direction, and how fast it is moving toward or away from the station. A transmitter sends out radio or microwave energy, pulsed or continuous, through an antenna, usually the same one that catches the reflections, and a receiver and processor work out the target's properties. It tracks aircraft, ships, spacecraft, missiles, vehicles, weather, and terrain, and serves air traffic control, radar astronomy, anti-collision systems, and weather forecasting. Lidar works on the same idea with infrared laser light.
Heinrich Hertz showed in 1886 that radio waves bounce off solid objects. In 1904 the German inventor Christian Hülsmeyer patented a device that detected a ship in thick fog, though it could not tell the distance. In 1922 A. Hoyt Taylor and Leo C. Young of the U.S. Navy noticed that ships crossing a radio beam over the Potomac made the signal fade in and out, and in the UK L. S. Alder filed a secret naval radar patent in 1928.
By the 1930s eight countries, among them France, Germany, Japan, and the Soviet Union, were pursuing radar. Robert M. Page at the Naval Research Laboratory demonstrated the first basic pulsed set in December 1934. In 1935 Robert Watson-Watt was asked about rumours of a German radio death ray; his colleague Wilkins calculated it was impossible but recalled that aircraft disturbed radio signals, and that insight led to the Chain Home stations.
From 1936 Watson-Watt led the Bawdsey Research Station in Suffolk, where the first five Chain Home stations were running that year; by 1940 the chain covered the whole UK. Crude even for its day, it was followed by the cavity magnetron, a British invention that allowed compact sets with sub-metre resolution and was shared with the United States on the 1940 Tizard Mission. The war drove lightweight radars for night fighters and patrol aircraft and aids such as Oboe for the RAF's Pathfinders.
Source: Radar
