Circularly Polarized High-Gain K-Band Liquid Crystal Phased Array Antenna

A $16\times 16$ liquid crystal (LC) phased array based on LC delay line phase shifters operating at 25.52 GHz is presented. We first propose and demonstrate a numerical model for calculating the relationship between the phase shift of an independent LC phase shifter and the external bias voltage. Then, we design a $16\times 16$ circularly polarized microstrip patch antenna array, combined with 256 spiral inverted microstrip delay line LC phase shifters. The whole array is fed by a rectangular waveguide power divider to maintain low radio frequency feeding loss. Via the measurements, we find that the LC phase shifter reveals a maximum differential phase shift of 370° under 0–8-V bias voltage. The beam of LC phased array can be steered continuously, covering ±30° in the elevation plane and 0°–360° in the azimuth plane. The measured gain at the broadside direction is 25.85 dBic, and the minimum axial ratio (AR) is 1.1 dB.

I. Introduction

With the development of satellite Internet and 6G communication, phased array antennas have enormous demand to be used as mobile terminals. However, the conventional phased array antennas are expensive, energy intensive, and bulky, which limits their application scenarios. There is a huge demand of low cost, low power consumption, and lightweight phased array antennas for mobile terminal applications in the coming 6G era. Liquid crystal (LC) phased array antenna is a competitive scheme to meet these requirements [1], [2]. LC material has many merits for microwave and millimeter-wave applications [3]. For example, LC is low cost and easily integrated. The dielectric loss of LC does not increase when the frequency increases in the microwave and millimeter-wave band. Comparatively, the parasitic effect of RF switches or varactor diodes usually leads to large loss in frequency bands above 10 GHz. So, LC-based phased array antenna is quite suitable for applications at frequencies higher than the Ku-band. The driving quasi-static bias voltage of LC phased array antenna is only several volts, which leads to low power consumption. LC phased array antenna can be fabricated using mature LC display technology, which makes it low cost and lightweight.