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.

I. Introduction

The continuous evolution of phased array technology has increased the demand for innovative advancements in phase shifter (PS) modules. One of the most critical requirements for a PS is low phase error, which significantly impacts the synthesized gain and beam focusing precision in phased array systems [1]. For a PS with a certain bandwidth, the phase error arises from inherent dispersion characteristics, which can only be reduced but cannot be fully eliminated. In addition, high power handling capability is essential for compatibility with power amplifiers (PAs) [2] or low-noise amplifiers (LNAs) [3], [4], to enhance system power thresholds and ensure stability. For high-power microwave (HPM) systems such as HPM phased arrays and HPM power synthesizers, HPM PSs with both low phase error and high power handling capability are highly desirable.