Pilot Tone Reference Less Phase Conjugator for Phase Modulated Retrodirective Antenna Applications
This letter presents a simple tracking phased locked loop (PLL) that can be used to track phase modulated signals and provide a phase conjugated signal for retrodirective retransmission. The configuration allows the retrodirective antenna to directly track phase modulated signals with no requirement for a separate continuous wave (CW) pilot tone. The ability to directly track phase modulated signals is carried out using a 4x multiplier on the tracking PLL reference signal. Practical phase conjugation results are presented for a five element retrodirective array simultaneously sending and receiving phase modulated (QPSK) signals. Signals with levels as low as 122 dBm can be phase conjugated and retransmitted with 30 dBm EIRP.
IEEE Antennas and Wireless Propagation Letters