An apparatus is provided for transmission of RF signals between a transmitter and a receiver. The apparatus includes a transmitter comprising a first retroreflector having a first array of sub-wavelength retroreflective elements at one end of an open cavity for transmitting RF seed signals. The apparatus also includes a receiver comprising a second retroreflector having a second array of sub-wavelength retroreflective elements at an opposite end of the open cavity for receiving the transmitted seed signal, the transmitted RF seed signals being in form of a beam directed toward the receiver.