A W-Band Bidirectional Vector Switching Phase Shifter Using a Directional Rat-Race Coupler

This letter presents a low-loss 360° bidirectional variable gain phase shifter that achieves vector-sum phase shifting without I/Q signal attenuation. The proposed phase shifter exhibits lower insertion loss than conventional designs through a directional rat-race coupler (RRC)-based asymmetric power dividing. Using transistor switches for phase states and double-pole double-throw switches (DPDTs) for variable gain, all the phase-shifted and variable gain states are achieved through separated phase and gain control without calibration. This reduces chip size and simplifies calibration and beamforming by replacing separate phase shifters and attenuators in the transmit (TX) and receive (RX) channels. The proposed phase shifter is fabricated using 28-nm bulk CMOS technology and has a size of 0.16 mm2 excluding pads. At 94 GHz, the root mean square (rms) phase error is 2.5°, rms gain error is 0.5 dB, and measured insertion loss is $13.2~\pm ~0.7$ dB without dc power consumption.