✔️📘✏️An airport surveillance radar (ASR) is a radar system used at airports to detect and display the presence and position of aircraft in the airspace around airports.
✔️📘✏️There are two types of surveillance radar- The primary and secondary surveillance radar.
✔️📘✏️The primary surveillance radar typically consists of a large rotating parabolic antenna dish that sweeps a vertical fan-shaped beam of microwaves. The target in line with the beam will reflect energy back to the antenna.
✔️📘✏️By measuring the time taken and noting the direction of the beam, the range and bearing of the target are found. Which is indicated on PPI (plan position indicator). It usually operates at a frequency of 2.7 - 2.9 GHz in S-band with peak radiated power of 25kW.
✔️📘✏️The second system is the secondary surveillance radar, or SSR, which depends on a co-operating transponder installed on the aircraft being tracked. The transponder emits a signal when it is interrogated by the secondary radar.
✔️📘✏️A discrete transponder code (often called a squawk code) is assigned by air traffic controllers to the aircraft, a four-digit code assigned to each aircraft that enters a region. Information about this aircraft is then entered into the system and subsequently added to the controller's screen to display this information when interrogated.
✔️📘✏️The secondary surveillance radar consists of a second rotating antenna often mounted on the primary antenna, which interrogates the transponders of aircraft, which transmits a radio signal back containing the aircraft's identification, barometric altitude, and an emergency status code, which is displayed on the radar screen. It operates at a frequency of 1.03 - 1.09 GHz in the L-band with peak power of 160 - 1500 W.