A 360° Tunable Phase Shifter With Low Phase Error Based on Bandpass Networks in 0.25- μm GaN Technology

This brief presents a 360° tunable phase shifter (PS) with low phase error in a 0.25- $\mu $ m GaN-on-SiC HEMT process. To achieve these features, the design incorporates two key innovations: a novel switched-bandpass phase-shifting cell (PSC) topology and a Q-learning-based optimization algorithm, both applied for the first time in monolithic microwave integrated circuit (MMIC) PS designs. The adverse effects of the charge trapping effect in GaN HEMT switches are mitigated by using a nonlinear equivalent circuit model. A PS prototype consisting of a fifth-order bandpass PSC and two third-order bandpass PSCs with a core area of $1.25\times 2.5$ mm2 is designed, fabricated, and measured. Experimental results demonstrate a low rms phase error of less than 7.0°, along with high power linearity characterized by an IP $_{\mathrm {1\,dB}}$ of 37 dBm and an IIP3 of 48 dBm, over a frequency range from 4.1 to 5.3 GHz.