A Compact 4-Bit PCM-Based Hybrid Phase Shifter in 0.18-μm SiGe BiCMOS for 28 GHz Phased Arrays

A fully-integrated, compact and low-loss 4-bit passive phase shifter (PS) employing Phase Change Material (PCM) switches is presented for Ka-band phased-array receivers. The design leverages the non-volatile and low-loss characteristics of PCM devices to enable a hybrid architecture that combines switch-type phase shifters for coarse phase control and a reflective-type network for fine phase resolution. This approach minimizes the number of active switching elements while preserving low insertion loss and compact integration. Fabricated in a 0.18 μm SiGe BiCMOS process, the PS achieves full 360° degree phase coverage with 22.5° resolution across 26.5–32.5 GHz. Measurements demonstrate an average insertion loss of 5.4 dB at 29 GHz and below 6 dB across the band, with root mean square (RMS) phase and amplitude errors under 7° and 1.5 dB, respectively. The RF core occupies only 0.096 mm², making the design well-suited for dense large-scale array implementations.