Liquid Crystal Based Parallel-Polarized Dielectric Image Guide Phase Shifter at W-Band

This paper presents a continuously tunable parallel-polarized dielectric image guide phase shifter, operating at W-Band (75 GHz to 110 GHz). The core material of the image guide is liquid crystal (LC), which is used to change the propagation constant of the guided wave. Four bias electrodes provide the field necessary to tune the LC. The parallel polarization reduces parasitic coupling to DC structures processed on the ground plane. Therefore, no stepped-impedance structure is necessary for the bias electrodes. Due to the image guide topology, the phase shifter can be used in substrate integrated environments. A maximum differential phase shift of 520° at 110 GHz is achieved with a bias voltage of +/-150 V while the insertion loss is between 3.7 dB to 4.3 dB. From 87 GHz on, the resulting maximum Figure-of-Merit (FoM) is higher than 100 °/dB, reaching a maximum of 125 °/dB at 103 GHz.