Sub-6 GHz High FOM Liquid Crystal Phase Shifter for Phased Array Antenna

Abstract

This paper presents a novel structure based on liquid crystal (LC) technology to achieve a high figure of merit $(FOM)$ phase shifter that works at sub-6 $GHz$ frequencies. The phase-shifting mechanism is enabled through the phase constant variation in the main microstrip line, which is loaded periodically by a variable equivalent capacitance controlled by a bias voltage. Furthermore, a systematic approach based on a transmission line circuit model and the periodic structure theory is developed as a fast method for design optimization by using the $ADS$ and $HFSS$ software. The fabricated phase shifter achieves a maximum insertion loss of 4.35 $dB$ and a maximum phase-shift of 461$^{\circ }$ at 4 $GHz$, which indicates an $FOM$ equal to 105.9$^{\circ }/dB$. Moreover, the phase shifter return loss is better than –10 $dB$ from 3.7 $GHz$ to 4.2 $GHz$, covering the sub-6 $GHz$ 5 G band. To validate the performance of the proposed phase shifter, a 1-D electronically steered phased array is designed, fabricated and tested by using a 4 ×4 aperture-coupled patch antenna array, excited by a continuous RF phase-shifting mechanism. The patch antenna array, as a 4-port radiation component, is designed with $HFSS$ full simulation, and achieved a fractional bandwidth of 30% at 4 GHz. The phased array prototype exhibits a continuous beam scanning over the elevation range of 0$^{\circ }$ to 20$^{\circ }$. According to the achieved $FOM$, and an integrable structure with the printed circuit board (PCB), the proposed low-cost and low power phase shifter is a good candidate for 5G application.

Keywords

• Phased array
• phase shifter
• liquid crystal (LC)
• patch antenna array
• beam steering
• beamforming