Compact 26–30 GHz Reflection-Type Phase Shifter With 8-Bit Switched Phase Tuning Utilizing Chalcogenide Phase-Change Switches

This article reports the first implementation of a 8-bit millimeter-wave (mmWave) reflection-type phase shifter (RTPS) based on phase change material (PCM) germanium telluride (GeTe). The switched phase shifter employs a compact co-planar waveguide (CPW)-based quadrature coupler in folded tandem configuration monolithically integrated with two identical reconfigurable reflective loads optimized to achieve a large phase shift range. Reconfigurability is achieved using eight identical latching PCM switches to load or unload a desired reflective load while consuming no static dc power. Various reflective load topologies are investigated for the optimum phase shift range over the operational bandwidth. The reflective load consists of either high-frequency metal-insulator-metal (MIM) capacitors. The resonance frequency of various states is pushed beyond 40 GHz to get a resonance-free tuning zone. The fully integrated phase shifter is highly miniaturized with an overall device footprint under
$0.98\times0.9$
mm, fabricated using an eight-layer in-house microfabrication process. The mmWave phase shifter demonstrates measured average insertion loss of 5.25 dB with only ±0.75 dB loss variation over 4 GHz bandwidth at 28 GHz center frequency. The proposed phase shifter exhibits a measured 280° linear phase shift in 256 discrete precision steps over 26 to 30 GHz with a figure-of-merit (FoM) of 53.3°/dB.