Patent ID: 8259000

Claim:
A Secondary Surveillance Radar (SSR) comprising a ground station including an antenna operable to receive an SSR reply signal including one or more S-Mode reply signals each having an S-Mode signal structure with preamble pulses, and/or one or more A/C-Mode reply signals each having an A/C-Mode signal structure with framing pulses; the ground station further including signal processing means coupled with the antenna to receive and process the SSR reply signal, and an S-Mode detector ( 20 ; 20 ′) coupled with the signal processing means to receive the processed SSR reply signal and designed to detect the S-Mode reply signal(s) in the SSR reply signal; the S-Mode detector ( 20 ; 20 ′) comprising: an S-Mode filter ( 21 ) matched to the preamble pulses of an S-Mode reply signal and operable to receive and filter the processed SSR reply signal to output an S-Mode filtered signal; characterized in that the S-Mode detector ( 20 ; 20 ′) further comprises: an S-Mode Constant False Alarm Rate (CFAR) device ( 22 ; 22 ′) coupled with the S-Mode filter ( 21 ) to receive the S-Mode filtered signal, and designed to detect an S-Mode reply signal in the SSR reply signal, so as to maintain a false alarm rate at a substantially constant value; and in that the ground station further includes an A/C-Mode detector ( 10 ) coupled with the signal processing means to receive the processed SSR reply signal and designed to detect the A/C-Mode reply signal(s) in the SSR reply signal, the A/C-Mode detector ( 10 ) comprising: an A/C-Mode filter ( 11 ) matched to the framing pulses of an A/C-Mode reply signal and operable to receive and filter the processed SSR reply signal to output an A/C-Mode filtered signal; and an A/C-Mode Constant False Alarm Rate (CFAR) device ( 12 ) coupled with the A/C-Mode filter ( 11 ) to receive the A/C-Mode filtered signal and designed to detect an A/C-Mode reply signal in the SSR reply signal, so as to maintain a false alarm rate at a substantially constant value.