Sub-6 GHz High FOM Liquid Crystal Phase Shifter for Phased Array Antenna
Mohammad Ali Panahi, Lap K. Yeung, Maziar Hedayati, Yuanxun Ethan Wang
Abstract
This paper presents a novel structure based on liquid crystal (LC) technology to achieve a high figure of merit <inline-formula><tex-math notation="LaTeX">$(FOM)$</tex-math></inline-formula> phase shifter that works at sub-6 <inline-formula><tex-math notation="LaTeX">$GHz$</tex-math></inline-formula> 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 <inline-formula><tex-math notation="LaTeX">$ADS$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">$HFSS$</tex-math></inline-formula> software. The fabricated phase shifter achieves a maximum insertion loss of 4.35 <inline-formula><tex-math notation="LaTeX">$dB$</tex-math></inline-formula> and a maximum phase-shift of 461<inline-formula><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> at 4 <inline-formula><tex-math notation="LaTeX">$GHz$</tex-math></inline-formula>, which indicates an <inline-formula><tex-math notation="LaTeX">$FOM$</tex-math></inline-formula> equal to 105.9<inline-formula><tex-math notation="LaTeX">$^{\circ }/dB$</tex-math></inline-formula>. Moreover, the phase shifter return loss is better than –10 <inline-formula><tex-math notation="LaTeX">$dB$</tex-math></inline-formula> from 3.7 <inline-formula><tex-math notation="LaTeX">$GHz$</tex-math></inline-formula> to 4.2 <inline-formula><tex-math notation="LaTeX">$GHz$</tex-math></inline-formula>, covering the sub-6 <inline-formula><tex-math notation="LaTeX">$GHz$</tex-math></inline-formula> 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 <inline-formula><tex-math notation="LaTeX">$HFSS$</tex-math></inline-formula> 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<inline-formula><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> to 20<inline-formula><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>. According to the achieved <inline-formula><tex-math notation="LaTeX">$FOM$</tex-math></inline-formula>, 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.