RADAR is a World War II acronym that stands for radio direction and ranging. A radar system consists of a radio transmitter and a receiver, where pulses of electromagnetic fields are transmitted from a transmitter, scattered (reflected or echoed) off of a target, and returned to a receiver. Round-trip time is measured from the moment the transmitted pulse is radiated to the moment the scattered pulse is received (Fig. 1.1). Radio waves travel through air at approximately the speed of light. By measuring the time delay, the range to target can be determined.