Dual-Frequency Retrodirective Array Adopting Cascode Resistive Mixer for Duplexing Communication

This article proposes a novel dual-frequency retrodirective array system introducing cascode resistive FET mixers in duplex mode. The cascode resistive FET mixer serves as a phase conjugation mixer (PCM) in Tx mode and an RF amplifier in Rx mode with the local oscillator (LO) port for dual paths of LO and RF signals, removing the need for a directional coupler to extract a modulated RF signal in Rx mode. The dual-frequency technique with a significant frequency gap and a high-order RF filter facilitates high data rate and long-distance communication. The RF and IF signals of 8.5 GHz (Rx) and 9.5 GHz (Tx), respectively, along with an RF band-stop filter (BSF), were used to achieve the desired frequency gap and high RF-IF isolation. The proposed retrodirective system supports full-duplex mode with ASK modulation and BPSK demodulation, as well as half-duplex mode with BPSK modulation and demodulation. The fabricated cascode resistive FET mixer showed a conversion gain of $6.6~\pm ~0.8$ dB with an LO power of 15 dBm in Tx mode and a gain of $11.5~\pm ~0.3$ dB in Rx mode at the frequency range of 8.45–8.55 GHz. The RF-IF isolation of the phase conjugator comprising the mixer and RSF was obtained as 24.2–33.8 dB at 8.45–8.55 GHz. The proposed retrodirective array system successfully demonstrated a 50-Mb/s BPSK data communication and achieved a 3-dB beamwidth of 100°, featuring autonomous retrodirective beam steering.