Patent ID: 7705770

Claim:
An IFF interrogation system for use on an aircraft, said system transmitting a signal from an interrogator to a transponder and a signal from said transponder to said interrogator, said system comprising an IFF transmitter and receiver, said IFF transmitter and receiver generating a sum signal and a difference signal, an IFF antenna, said IFF antenna establishing a link with said transponder and transmitting a sum and difference signal to said transponder, said IFF antenna receiving a signal from said transponder, said IFF antenna breaking said link via either an uplink signal or downlink signal when said uplink signal or said downlink signal has said difference signal greater than said sum signal at any given angle outside a main beam, a plurality of non-reciprocal auxiliary antenna elements, said non-reciprocal auxiliary antenna elements transmitting the difference signal, wherein at any given angle the sum beam gain is not greater than the difference beam gain on both transmit and receive.