Single-mode-dual-band to dual-mode-single-band bandpass filter with liquid metal

A mode-reconfigurable Butterworth bandpass filter, which can be switched between operating as a single-mode-dual-band (SMDB) and a dual-mode-single-band (DMSB) filter is presented. The filter is realized using a substrate integrated waveguide in a square cuboid geometry. Switching is enabled by using empty vias for the SMDB and liquid metal filled vias for the DMSB. The first two modes of the SMDB resonate 3 GHz apart, whereas the first two modes of the DMSB are degenerate and resonate only at the higher frequency. This is due to mode shifting of the first frequency band to the second frequency band. Measurements confirm the liquid-metal reconfiguration between the two operating modes.