Miniaturized SIW Cavity Tri-Band Filter Design

This letter presents a novel tri-band filter design using an ultraminiaturized substrate-integrated waveguide (SIW) cavity operated at evanescent mode. Two miniaturized SIW cavities in a face-to-face form are vertically stacked to build the proposed tri-band filter. The top and bottom metal layers form the cavity's broadside walls, and the middle layer possesses three identical patches which are formed by evenly trisecting a circular patch. These patches are shorted to the cavity's bottom wall through one, two, or four via-holes. The patches together with the host cavity exhibit three frequency-distinct resonances that create the filter's triple passbands. The resonance frequencies are independently controlled, and six passband-edge transmission zeros are created for good selectivity. The filter size is only 0.22 λ
_d
× 0.22 λ
_d
, and the measured in-band minimum insertion losses are 2.31, 2.25, and 3.01 dB for the first, second, and third bands, respectively. It is believed that the proposed tri-band filter has obtained the best circuit area efficiency in the SIW tri-band filter category.