Retrodirective antenna systems

A retrodirective antenna system for receiving an incoming signal from an object and directing an outgoing signal back to the object, comprising two or more transceiver cells, each of which receives a part of the incoming signal, produces a phase conjugate output signal, which output signals from the cells combine to form an outgoing signal directed back to the object, wherein each transceiver cell comprises an antenna component which detects the part of the incoming signal, a processor which receives the part of the incoming signal and produces first and second same-side, sideband (SB) signals of the part of the incoming signal, a phase shift system comprising a first phase element which receives the first SB signal and outputs a SB signal having a first phase, and a second phase element which receives the second SB signal and outputs a SB signal having a second phase which is in quadrature with the first phase, and an IQ modulator comprising an I input port, a Q input port and a phase adjuster, which receives the SB signal having the first phase on the I input port and the SB signal having the second phase on the Q input port, or receives the SB signal having the first phase on the Q input port and the SB signal having the second phase on the I input port, and phase adjusts the SB signals to produce an output signal which is the phase conjugate of the part of the incoming signal.