A Compact Quasi-Circulator with High Isolation Using Reconfigurable 180° Hybrid

A compact tunable quasi-circulator (QC) with high isolation using a reconfigurable 180° hybrid is proposed in this paper. Such hybrid consists of six phase shifters with loaded varactors to achieve frequency tuning operation. To improve the isolation, an impedance balance resistor is employed and tapped in the hybrid. A power amplifier (PA) and a low noise amplifier (LNA) are utilized to enhance the performance of transmitter (TX) and receiver (RX) paths, respectively. Then, to verify the mechanism of structures mentioned above, a tunable QC is implemented, fabricated, and measured. The measurement exhibits a frequency tuning range of 2.9–3.7 GHz. The in-band TX-RX isolation is 24–40 dB, and the RX gain is higher than 4.6 dB while the NF is lower than 5.9 dB, respectively. Meanwhile, the TX gain>4.5 dB, a output 1-dB compression point (P1dB) of 21.3 dBm with power efficiency of 12.7% at 3.3 GHz are achieved.