(RADAR) is an acronym for RAdio Detection And Ranging; it is an object detection system that uses radio waves to determine the range, angle, or velocity of objects. It can detect aircraft, ships, spacecraft, and missiles. RADAR was developed in the 1930s and 1940s by several nations as a defense against enemy aircraft and missiles.
RADAR works by sending out a pulse of radio waves and then measuring the time it takes for the waves to bounce back off of an object. The returning waves are then analyzed to determine the distance, direction, or speed of the object. RADAR can be used in both active and passive modes; in active mode, RADAR transmits a signal while in passive mode radar only receives signals that are already present.
Many RADAR systems have been developed for specific applications such as air traffic control, weather monitoring, maritime navigation, etc. Every kind of RADAR system operates slightly differently but shares common principles. As technology has progressed, so has our ability to build smaller, more sophisticated RADAR systems, which means they can now be found in everything from cars (Adaptive Cruise Control) to cell phones (Google Maps).