<P> Radar is an object - detection system that uses radio waves to determine the range, angle, or velocity of objects . It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain . A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna (often the same antenna is used for transmitting and receiving) and a receiver and processor to determine properties of the object (s). Radio waves (pulsed or continuous) from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed . </P> <P> Radar was developed secretly for military use by several nations in the period before and during World War II . A key development was the cavity magnetron in the UK, which allowed the creation of relatively small systems with sub-meter resolution . The term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging or RAdio Direction And Ranging . The term radar has since entered English and other languages as a common noun, losing all capitalization . </P>

An advanced weather data measurement tool that sends out radio waves is called a(n)