An SSR antenna having a polar diagram which is designed to “cover” the side lobes of the main interrogating antenna. It is used to radiate a control pulse which, if it exceeds in amplitude the associated interrogation signal at the input to the transponder, will cause the transponder to inhibit responses to the interrogation pulses. Modern SSR antennas have the control elements built into the main array. The control antennas is also known as the SLS (side-lobe suppression) antenna.
ICAO (2004) doc. 9684, Manual of the Secondary Surveillance Radar (SSR) Systems