English: The antenna system of an Airport Surveillance Radar-9 with primary radar (parabolic antenna) and secondary radar (rectangular antenna, top). The secondary radar interrogates the transponder on the aircraft, which sends back a coded signal indentifying the craft and giving its altitude.
Source
FAA ASR-9/Mode S Service Life Extension Program Photogaller, transfered from English Wikipedia where it was uploaded originally by w:en:User:Dmcdevit
Transwiki approved by: w:en:User:Dmcdevit This image was copied from wikipedia:en. The original description was: The antenna system of an Airport Surveillance Radar-9 ''Source: FAA ASR-9/Mode S Service Life Extension Program Photogallery'' {{PD-US