A retro-directive antenna array with phase conjugation circuit using subharmonically injection-locked self-oscillating mixers

In this paper, a novel phase conjugation circuit and its application to retro-directive antennas are presented. The phase conjugation circuit uses a balanced circuit structure with subharmonically injection locked self-oscillating mixers oscillating at ω. In the operation, an input signal at ω/2 is converted to its conjugated signal with no external source required for LO signal pumping, and the output signal frequency is locked at the same frequency of the input signal. The developed phase conjugation circuit is implemented with active antennas to become a retrodirective antenna array. Both the theoretical and measured results of phase conjugation and retro-directive performance are shown in good agreement.