Program:

Airport Surveillance Radar (ASR-11) is an integrated primary and secondary radar system that has been deployed at terminal air traffic control sites. It interfaces with both legacy and digital automation systems and provides six-level national weather service calibrated weather capability that provides enhanced situational awareness for both controllers and pilots.

Primary and Secondary Surveillance Radar:

The primary surveillance radar is a 60 nautical mile S-Band radar (2700 to 2900 MHz) with peak effective power of 25kW. The radar uses a continually rotating antenna mounted on a tower that range between 25–75 feet tall.  

The primary radar transmits electromagnetic waves (radar beams) that travels in a straight path until an aircraft or object interrupts the radar beam. When the radar beam is interrupted, the beam is then reflected from the surface of an aircraft or object back to the radar antenna. The radar system measures the time required for the radar beam to return and the azimuth (direction) of the beam. The system then determines the distance of the aircraft from the radar antenna by measuring the time it takes to receive the radar beam reflection. The aircraft’s actual location is determined by combining the distance and the azimuth of the reflected radar beam. 

The secondary surveillance radar uses a second radar beacon antenna attached to the top of the primary radar antenna to transmit and receive area aircraft data for barometric altitude, identification code, and emergency conditions. Military, commercial, and some general aviation aircraft have transponders that automatically respond to a signal from the secondary radar by reporting an identification code and altitude. The Air Traffic Control centers uses this system data to verify the location of aircraft. The secondary radar also provides rapid identification of aircraft in distress. The secondary radar operates in the L-Band at the frequency of 1030 to 1090 MHz.