Tunable Ultra-Wideband (UWB) Liquid Metal Phase Shifter Based on SISL Platform

In this article, a novel tunable phase shifter operating in the ultra-wideband (UWB) is proposed. The transmission phase can be changed by tuning the length of the transmission line. A stretchable line is utilized according to this theory, consisting of eutectic gallium-indium (EGaIn) liquid metal (LM) as the inner conductor and a flexible polydimethylsiloxane (PDMS) tube as the outer shell. The LM line is placed in substrate integrated suspended line (SISL) cavity. To accurately calculate the characteristic impedance of the LM line within the SISL cavity, a coaxial model comprising a circular inner conductor and rectangular outer conductor is employed. A high-pass and low-pass matching circuit is designed using SISL double metal layers on Sub3 to improve matching and out-of-band suppression of the LM phase shifter at UWB. Two types of LM phase shifters were designed and manufactured: the basic LM phase shifter meeting 5.3–7.6 GHz frequency band with a phase shift range from 308° to 450°, and the UWB LM phase shifter operating at 3.1–10.6 GHz with a phase shift range from 164° to 552°, respectively. Additionally, an automatic control system based on microcontroller and stepper motors is implemented for mechanical elongation in achieving precise control over desired phase shifts through mechatronics.