Wideband PCB-to-Connectors Impedance Adapters for Liquid Crystal-based Low-loss Phase Shifters

This paper presents the design, optimisation and experimental verification of a wideband impedance adapting network for a liquid crystal (LC) based electronically-tuned phase shifter device including connectors operating up to 67GHz. In contrast with conventional frequency-domain methods based on cross-sectional study assuming an infinitely long transmission line, a time-domain reflectometry (TDR) method is proposed in this work to quantify the transient impedance, and optimise the electrically-short PCB transition part between 1.85mm coaxial connectors and the tunable LC part packaged in an enclosed coplanar waveguide. The fabricated device exhibits a return loss lower than -15dB from 20MHz up to 67GHz, and a maximum insertion loss less than -5.6dB for a differential phase shift of 180°, which delivers a wideband low-loss solution for states-of-the-arts in LC-based phase shifter devices with connectors.