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Definition of RADAR
: a device or system consisting usually of a synchronized radio transmitter and receiver that emits radio waves and processes their reflections for display and is used especially for detecting and locating objects (as aircraft) or surface features (as of a planet)
: range of notice <fell off the radar after losing their first three games>
System that uses electromagnetic echoes to detect and locate objects. It can also measure precisely the distance (range) to an object and the speed at which the object is moving toward or away from the observing unit. Radar (the name is derived from radio detecting and ranging) originated in the experimental work of Heinrich Hertz in the late 1880s. During World War II British and U.S. researchers developed a high-powered microwave radar system for military use. Radar is used today in identification and monitoring of artificial satellites in Earth orbit, as a navigational aid for airplanes and marine vessels, for air traffic control around major airports, for monitoring local weather systems, and for spotting speeders.