Compact Single-Cavity Dual-Band SIW Filter Based on Orthogonal Hybrid Loading

Abstract

A compact, high-selectivity, dual-band substrate-integrated waveguide (SIW) filter is proposed in this paper based on an orthogonal hybrid loading scheme. To address the inherent trade-off among circuit size, frequency selectivity and tuning flexibility in conventional single-cavity dual-band SIW designs, two symmetrical capacitive conductive posts and three central inductive metallised vias are orthogonally integrated into a single cavity to reconstruct the first four resonant modes for dual-passband operation. The capacitive posts modulate higher-order resonant modes to support mode reconstruction, lowering the lower passband frequency for miniaturisation and quasi-independent tuning. The inductive vias regulate the inter-mode coupling strength to generate two controllable transmission zeros and achieve independent bandwidth adjustment for both passbands. A filter prototype is implemented using the multilayer PCB process. It occupies a compact footprint of 0.76 λg² and operates at 5.48 and 8.36 GHz with 3-dB fractional bandwidths of 3.8% and 5%, respectively.