radar

Radar is an acronym for radio detection and ranging. It is a detection system that uses radio waves to determine the range, bearing, and, in many systems, relative velocity of objects such as aircraft, ships, weather fronts, and terrain. A radar transmits radio signals and listens for echoes reflected from targets. Time delay between transmission and reception provides range, while Doppler shift of the returned signal can indicate relative speed.

Radar development began in the 1930s, with early work in Britain led by Sir Robert Watson-Watt and colleagues, and rapid progress in the United States during World War II. After the war, advances in solid-state electronics, signal processing, and phased arrays expanded radar capabilities for civilian and military use.

A typical radar system includes a transmitter, a transmitter/receiver antenna, a receiver, signal-processing electronics, and a display or data-processor. Some systems share the same antenna for transmission and reception using a duplexer. Modes include pulsed radar, which measures range from timing, and continuous-wave or FMCW systems, which can measure range with high precision and/or velocity with Doppler processing. Antenna design and frequency influence resolution and detection range.

Radar applications span air traffic control, weather monitoring, maritime navigation, defense and surveillance, automotive safety, and remote sensing. Imaging radars such as synthetic-aperture radar (SAR) and weather radars provide two- or three-dimensional views of scenes.

Limitations include susceptibility to atmospheric attenuation, precipitation clutter, and interference; target cross-section variability; regulatory constraints on frequency bands; and potential vulnerability to jamming or spoofing. Its effectiveness depends on transmitter power, receiver sensitivity, and signal processing.