A Van Atta array is a type of passive retrodirective phased array antenna which redirects (rather than reflects) a signal back in the direction from which it came. It was first described by Lester C. Van Atta in his 1959 patent. [1]
The signal can be modulated by the redirecting host for purposes such as radio-frequency identification and traffic control (radar target echo enhancement). [2]
A 2023 paper describes the extension of the van Atta antenna principle to underwater acoustic communication. [3]