Novel retrodirective beam formation techniques

This paper presents two novel active antenna architectures for retrodirective beam formation which rely on heterodyne phase techniques for their operation. Both the methods use the phase conjugate properties of a mixer driven with f0 and 2f0 signals for retrodirective beam formation. In the first approach frequency diversity, coupled with power divider circuits is used as a quasi circulator to provide isolation between incident and retransmitted signals. In the second method a dual linearly polarised microstrip patch antenna provides the complementary function of radiator and isolation element by virtue of its polarisation diversity response. Two element arrays using both approaches were made for 1 GHz operation. Results and theoretical performance figures for the retrodirective antenna architectures are presented in the paper and are compared to a passive 2 element array which is used as a reference for discussion.