Widely-Reconfigurable 2.5:1 Coaxial-Cavity Resonators Using Actuated Liquid-Metal Posts

This paper reports on a new method for tuning the resonant frequency of coaxial cavity resonators beyond one octave (2.5:1). The proposed tuning mechanism is based on pneumatically-actuated liquid metals (LMs) that functionalize a variable-height post-inner conductor-of a coaxial cavity resonator. The employed LM is an eutectic alloy of Gallium, Indium and Tin-commonly known as Galinstan-that is filled inside a Teflon-based tube. It is demonstrated that by altering the amount of Galinstan within the LM-based post, wideband continuous RF tuning can be achieved. For proof-of-concept demonstration purposes a tunable coaxial cavity resonator was designed, manufactured and measured. It demonstrated center frequency tuning between 4 and 10 GHz that corresponds to a 2.5: 1 tuning range. For these frequencies, the unloaded quality factor of the resonator was measured between 225 to 630, demonstrating the potential of LM tuning for low-loss and widely-reconfigurable RF filters.