Miniaturized SIW Cavity Resonator and Its Application in Filter Design

The contribution of this letter is to propose an evanescent-mode ultraminiaturized substrate integrated waveguide (SIW) cavity resonator and its application in bandpass filter (BPF) design. The proposed compact SIW cavity is composed of two dielectric substrates with three metal layers. The top and bottom metal layers form the cavity's broadside walls, and the middle one is a circular patch that shorts to the bottom wall by a ring fence of vias (or a centered single via). This circular patch together with the ring-fence vias (or single via) provides cavity resonator a large loading capacitance to allow a dramatic frequency downshift. Two experimental four-pole BPFs are built to validate the circuit design. The achieved frequency downshift of the proposed SIW cavity, compared with that of its conventional SIW cavity counterpart, is 72.5% (82.3%) for the via-ring fence (single via) case. Not only is the associated area miniaturization factor (MF) comparable with the highest record in the literature, but also the BPFs implemented here are structurally simpler and exhibit a much wider relative upper stopband bandwidth than that of the SIW BPF with a record of high MF.