A millimeter wave retrodirective transponder for collision/obstacle avoidance and navigation/location

A small, low power drain and low cost transponder are described, which have numerous automotive applications. The principle of operation of the retrodirective transponder (RDT) is based on the Van Atta array which has the ability to take an incident RF wave and re-radiate it back in the direction from which it cam, i.e., retrodirectively. While passing through the RDT's integral monolithic GaAs modulators, the RF wave can be modulated by information that is thereby automatically transmitted back to the interrogator. The operation of the modulatable Van Atta array is illustrated.