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A retrodirective system reacts to an incoming signal from an unspecified direction by transmitting a response to that same direction, regardless of what that direction is. This automatic beamsteering feature, performed without any prior knowledge of the location of the source, makes retrodirective systems attractive for automatic pointing and tracking systems, microwave‐tracking beacons, radiofrequency identification, solar power satellites, and small‐satellite crosslinks. This article focuses on retrodirective antenna arrays and their applications and characterization. After reviewing the two basic retrodirective array architectures (Van Atta and phase‐conjugating arrays), several two‐dimensional and millimeter‐wave arrays are then discussed, as well as several key applications in wireless communications.

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