Airport surveillance radar

An airport surveillance radar (ASR) is a radar system used at airports to detect and display the position of aircraft in the terminal area, the airspace around airports. The sophisticated systems at large airports consist of two different radar systems, the primary and secondary surveillance radar. The primary radar typically consists of a large rotating parabolic antenna that sweeps a vertical fan-shaped beam of microwaves around the airspace surrounding the airport which detects the position of aircraft. The secondary surveillance radar consists of a second rotating antenna, often mounted on the primary antenna, which interrogates the transponders of aircraft, which transmits back the aircraft's identification and altitude which is displayed on the radar screen next to the return from the primary radar.