An active subharmonic retrodirective array using dual polarized microstrip antennas

Summary form only given. Retrodirective antennas have the unique characteristic that, when they are illuminated by a signal, the array transmits the return signal towards the source direction without any prior information on its location. We discuss a novel architecture for an active retrodirective array using subharmonic mixers. The mixers use FETs as the primary mixing elements. The retrodirective array uses a new design for dual polarized microstrip antennas fed by conductor-backed coplanar waveguides. We use the heterodyne mixing principle to achieve retrodirectivity. Phase conjugation with heterodyne mixing uses an LO signal at twice the RF frequency. In this scheme, the lower sideband product has the same frequency as the RF, but with a conjugated phase. Subharmonic mixing is employed to ease the LO drive frequency requirement which makes it cost effective at higher frequencies. A coplanar waveguide fed slot ring hybrid is built to realize the balanced mixer; which provides a good LO-IF isolation. Theoretical simulations have been used to optimize the retrodirective array and the antenna. The dual polarized, conductor-backed antenna has impedance bandwidth of 15%, and isolation between the two ports is found to be more than 25 dB.