A modulating signal which is selectively changed as a function of time is applied to the modulating diodes of a retrodirective array. The diodes modulate the signal reflected from the array. A decoder coacting with the illuminating radar can extract information from the time-frequency code superimposed...http://www.google.com/patents/US4210910?utm_source=gb-gplus-sharePatent US4210910 - Decoder for a space retrodirective array
