A Hybrid Analog–Digital Reflective–Type Phase Shifter Integrating BST Varactors and GeTe Switches With Continuous Phase Control

Abstract

This paper presents a hybrid analog–digital reflective–type phase shifter (RTPS) achieving continuous $360^\circ$ phase coverage over the 37–40 GHz frequency range. The proposed architecture addresses the fundamental limitations of purely analog and purely digital RTPS implementations by combining one analog stage with two digital stages. The two digital stages utilize GeTe phase-change material switches to realize coarse phase shifts of $180^\circ$ and $90^\circ /45^\circ$, while the analog stage employs a BST varactor-based reflective load to provide continuous fine phase tuning between the states. The phase shifter is implemented using a compact tandem-coupler-based RTPS topology and fabricated using a monolithic fabrication process integrating BST varactors and GeTe switches. Measurement results show continuous $360^\circ$ phase tuning with an insertion loss ranging from 6.1 to 9.8 dB. The proposed design demonstrates an effective trade-off between phase coverage, resolution, and insertion loss, making it well suited for millimeter-wave phased-array applications.