radar

Device for locating objects in space, direction finding, and navigation by means of transmitted and reflected high-frequency radio waves.

The direction of an object is ascertained by transmitting a beam of short-wavelength (1–100 cm/0.5–40 in), short-pulse radio waves, and picking up the reflected beam. Distance is determined by timing the journey of the radio waves (travelling at the speed of light) to the object and back again. Radar is also used to detect objects underground, for example service pipes, and in archaeology. Contours of remains of ancient buildings can be detected down to 20 m/66 ft below ground. Radar is essential to navigation in darkness, cloud, and fog, and is widely used in warfare to detect enemy aircraft and missiles. To avoid detection, various devices, such as modified shapes (to reduce their radar cross-section), radar-absorbent paints, and electronic jamming are used. To pinpoint small targets laser ‘radar’, using light instead of radio waves, has been developed. Radar was developed independently in Britain, France, Germany, and the USA in the 1930s. It was first put to practical use for aircraft detection by the British, who had a complete coastal chain of radar stations installed by September 1938. It proved invaluable in the Battle of Britain in 1940, when the ability to spot incoming German aircraft did away with the need to fly standing patrols. Chains of ground radar stations are used to warn of enemy attack – for example, North Warning System 1985, consisting of 52 stations across the Canadian Arctic and northern Alaska. Radar is also used in meteorology and astronomy.