We propose a miniaturized bandpass filter (BPF) design with enhanced signal selectivity performance. The proposed structure is composed of four square substrate integrated waveguide cavities (SIWCs). To miniaturize its circuit size, the applied cavities are under the evanescent mode resonance which is accomplished by loaded itself with a large capacitance. As a result, a 93.4% size reduction is achieved. The negative coupling structure is employed in the filter design to create two transmission zeroes by the pass band's two edges for enhancing the signal selectivity. Experiment is conducted to verify this compact SIWC BPF design.
