Super Cavity Region Substrate Integrated Waveguide Bandpass Filter

A compact 4-pole substrate integrated waveguide (SIW) bandpass filter exploiting the supercavity (SC) region is demonstrated. By cascading two pairs of high-index resonators (HIRs)-SIW resonators, strong mode hybridization close to epsilon near zero (ENZ) region generates a broadband SC region rather than a single resonance. The fabricated resulting filter achieves 11% bandwidth at 2.35 GHz with >35 dB rejection and the measured unloaded Q reaches to 340, while the filter occupys an area of only 4.5% λ₀². The proposed SC-region coupling mechanism enables simultaneous miniaturization, high selectivity, and wideband performance, offering a new pathway for integrated SIW filters with interference-driven broadband supercavity operation.