Liquid Metal-Based Tunable Linear Phase Shifters With Low Insertion Loss, High Phase Resolution, and Low Dispersion

A linear, tunable, and self-compensating phase shifter based on liquid metal (LM) is proposed in this paper using a half-mode substrate-integrated-waveguide (HMSIW). The key phase shifting element is a via-pad-slot (VPS) structure where a thru via is attached to a pad surrounded by an annular slot. This is equivalent to a shunt capacitance and inductance loaded on the HMSIW. Phase shift is achieved when the annular slot is covered by the LM that runs in microfluidic channels on the surface of the HMSIW. This allows easy implementation and convenient manipulation of the LM without incurring excessive losses. A self-compensation structure, based on multiple rows of VPSs, is proposed to achieve a low phase deviation with frequency (low dispersion). The design method to ensure a linear and small phase step over a large phase range is presented. Two phase shifters have been designed and experimentally verified. The phase shifter-I, with two VPS rows, provides a phase shift from 0 to 41° with ±1° phase deviation with frequency over 9.5 - 12.5 GHz. The average phase resolution is 1°. The measured insertion loss (IL) is 0.8 ± 0.1 dB, with a figure-of-merit of 45.6°/dB. The phase shifter-II uses three VPS rows to provide a phase shift from 0° to 180° with a phase resolution of 1.68°. The achieved phase deviation with frequency is within ±2° over 10 - 12.5 GHz and within ±5° over 9 - 13 GHz. The measured IL is 1.1 ± 0.1 dB with a competitively high figure-of-merit of 163.6°/dB. Unlike many other phase shifters, the loss of the proposed phase shifters does not increase with the phase shift. The measurements are in very good agreement with the circuit analysis and simulations. The proposed linear phase shifter has demonstrated high performance and very attractive features such as low IL that does not strongly depend on the phase shift, linear phase change, high phase resolution, and low phase dispersion with frequency. Compared with other LM-enabled phase shifters, it has the advantage of easy implementation and control. This LM-based phase shifter also potentially has high power handling capability.