A reconfigurable quarter-mode substrate integrated waveguide cavity filter employing liquid-metal capacitive loading

A microfluidically-tunable substrate integrated cavity filter is presented for the first time. Quarter mode cylindrical substrate integrated waveguide (SIW) cavities are used to design an ultra-compact two-pole filter with a center frequency of ~1.12 GHz. A corner via is connected to a surface ring gap in order to capacitively load each SIW cavity resonator. Frequency tuning of the filter is achieved using the capacitive loading effect of a liquid metal channel placed on top of the surface gap capacitors. The Polydimethylsiloxane (PDMS) structure including the micro-channel is bonded to the SIW circuit board using a unique fabrication technique. Measured results verify a tuning ratio of 1.72;1 and an insertion loss of 2.5 and 3.45 dB at 1.12 and 0.65 GHz, respectively.