A Low-Loss Defected-Ground-Structure Based Phase Shifter and Antenna on a 4-μm Thin Liquid Crystal Layer

In this paper, a liquid crystal (LC) phase shifter is proposed using a defected-ground-structure (DGS) transmission line on a 4-
$\mu \text{m}$
-thin LC layer. The DGS transmission line is a modified micro-strip line that improves phase shift and loss in a 4-
$\mu \text{m}$
-thin LC layer by partially removing the ground plane. The phase shift is achieved through the variation of the LC dielectric constant caused by the bias voltage of the DGS transmission line. The proposed DGS phase shifter exhibits the highest figure-of-merit (FoM) of 61.5°/dB at 30 GHz. Furthermore, the phase shifter exhibits an rms phase error of less than 20° at 26-30 GHz and a 1-dB compression point of 30 dBm with 2.5° phase error at 35 dBm. To demonstrate the feasibility of the LC-based antenna array systems, the DGS phase shifter is combined with a patch antenna, resulting in a gain of 0 dBi and 360° phase shift at 18 GHz. The thin LC layer and high FoM make the proposed DGS phase shifter a suitable solution for use in large phased array systems and reconfigurable intelligent surfaces.