Frequency-Agile Bandpass Filters Using Liquid Metal Tunable Broadside Coupled Split Ring Resonators

A fluidic-based approach for designing tunable coupled resonator bandpass filters is presented. These filters employ broadside coupled split ring resonators (BC-SRR) with one of their open loop resonators constructed from liquid metal. The tuning mechanism is based on dynamically moving the liquid metal to reshape the resonator. To demonstrate the concept, a second order Butterworth filter with continuous tuning range from 650 to 870 MHz is designed and experimentally verified by utilizing PTFE tubing filled with liquid metal and Teflon solution. Due to an inductive external coupling mechanism and 180^° rotated resonators, the filter exhibits a near constant 5% fractional bandwidth throughout its tuning range with > 10 dB return and <; 3 dB insertion loss. The filter is realized over a 1.27 mm thick Rogers 6010.2LM substrate and has an approximate footprint of 20 × 40 mm².