Patent ID: 7663531

Claim:
A secondary surveillance radar system comprising a ground system which observes an observation area where an aircraft equipped with a mode S transponder and an aircraft equipped with an ATCRBS transponder possibly coexist, wherein the ground system comprises: a transmit processor which transmits to the observation area an all-call interrogation signal specific for mode S including an identification code of the ground system; a receive processor which receives a reply signal to the interrogation signal transmitted by the transmit processor; and a recognition processor which recognizes the reply signal as a processing target when identification information included in the reply signal received by the receive processor coincides with the identification code of the ground system, wherein the recognition processor recognizes the reply signal as the processing target also when the identification information included in the reply signal received by the receive processor coincides with null information, wherein the recognition processor gives distinguishable distinction information to the reply signal in which the identification information coincides with the identification code of the ground system and to the reply signal in which the identification information coincides with the null information, and wherein the ground system destroys a squitter reply recognized as the processing target with correlation processing using the distinction information.