W-Band Liquid-Metal-Enabled Phase Shifter: Linear Tunability and Self-Compensatory Phase Response

This paper proposes a W-band liquid metal (LM)-enabled linearly tunable substrate-integrated-waveguide (SIW) phase shifter with phase self-compensation. The switchable element is composed of a Via-Pad-Slot (VPS) structure. The via and pad are separated from the top-layer ground by an annular slot. The equivalent circuit of the VPS structure comprises a shunt capacitance and inductance. When it is covered by gallium (Ga)-based LM, the slot and equivalent capacitance disappear. When the VPS structures are covered by LM one by one, the phase linearly increases from 0° to the maximum of 360°. Since the shunt capacitance and inductance have phase compensation properties, the proposed phase shifter has a low phase deviation with frequency. The measured insertion loss (IL) is 2.6 dB at 80 GHz, and the phase shift ranges from 0° to 335° over 75 - 85 GHz. The phase shift step is 10.5°/via, and the phase deviation is approximately ±20°. This linear tunable phase shifter with low IL and phase deviation may find applications in millimetre-wave phased arrays.