Patent ID: 7408498

Claim:
A secondary surveillance radar, comprising: transmitting means for repeatedly transmitting interrogation signals from a beam antenna; receiving means for receiving response signals for the interrogation signals; and management processing means for dividing each of interrogation repetition cycles into two time periods, which are an all-call period to perform transactions for a transponder of an air traffic control radar beacon system (ATCRBS) and a mode S and a roll-call period to perform selective transactions for a mode S transponder and varying azimuth angle ranges for transmitting interrogations in accordance with prediction angle ranges of targets in the roll-call period, wherein the management processing means obtains and compares a beam-width of the antenna with the prediction angle ranges, performs selective interrogations at every roll-call period if the prediction angles ranges are narrower than the beam-width, and thins out the selective interrogations at every roll-call period by reducing transmission times of the interrogation by prescribed intervals if the prediction angle ranges are wider than the beam-width.