Liquid Crystal-Filled 60 GHz Coaxially Structured Phase Shifter Design and Simulation with Enhanced Figure of Merit by Novel Permittivity-Dependent Impedance Matching

This work serves as the first simulation investigation to tackle the liquid crystal (LC)-filled coaxially structured continuously variable phase shifter at 60 GHz, wherein the LCs act as single tunable dielectrics fully occupying the millimeter-wave (mmW) power transmitted (i.e., free of leakage or interference). Impedance and effective dielectric constant computations are settled, followed by the quantification of the interplay between the dielectric thickness and the dielectric constant (Dk) for a controlled 50 ohm impedance. Geometry's aspect ratio (AR) effects are exploited for the coaxially accommodating topology filled with mmW-tailored LCs with an operatable Dk range of 2.754 (isotropic state) to 3.3 (saturated bias state). In addition to the proposed structure's noise-free advantages, a novel figure of merit (FoM) enhancement method based on Dk-selection-based impedance matching is proposed. The optimum FoM design by simulation exhibits a 0-180.19 degrees continuously variable phase shift with a maximum insertion loss of 1.75871 dB, i.e., a simulated FoM of 102.46 degrees/dB when the LC-filled coaxial geometry is 50 ohm and matched with the Dk of 2.8, corresponding to the dielectric thickness of 0.34876 mm and line length of 15.92 mm. The envisioned device fabrication and assembly processes are free of the conventional polyimide alignment agent and the related thermal and electrical concerns. Significant cost reduction and yield improvement can hence be envisaged. The topology can also serve as a test structure for broadband characterizations of LC materials and new electro-optical effects.