A Miniaturized and Low-Loss Phase Shifter Based on Slow-Waves and Liquid Crystal

This article proposes a miniaturized, low-loss, and continuously tunable slow-wave (SW) liquid crystal (LC) phase shifter, designed specifically for the 60GHz millimeter-wave band. The 60GHz frequency range, with its wide bandwidth and short wavelength, enables compact and high-performance designs, making it ideal for next-generation communication systems. A three-parallel-stub slow-wave unit, incorporating fine rectangular branches and gaps, is proposed to enhance the slow-wave effect. A rectangular defected ground structure (DGS) is introduced to increase the bandwidth, while gradient stubs in the coplanar waveguide (CPW) are employed to improve impedance matching between the CPW port and the inverted microstrip line (IMSL) port. The equivalent circuit model of the proposed slow-wave unit is analyzed, and the evolutionary process of the structural design, along with its impact on phase velocity, is examined through comparison. Measurement results indicate that the structure achieves a phase shift of up to 250°/λ and a figure of merit (FoM) of 41.7°/dB, with an insertion loss of more than -6 dB. The simulation and measured results are in good agreement, demonstrating the feasibility of the proposed design in the 60GHz band.