Substrate-integrated-waveguide signal-interference bandpass filters

Abstract

This paper demonstrates the first experimental development of transversal signal-interference bandpass filters (BPFs) in substrate-integrated-waveguide (SIW) technology. They consist of bi-path transversal filtering sections (TFSs) that are based on 3-dB hybrid rings that are loaded with short-ended stubs in two of their ports. To attain circuit-size reduction in the overall TFS, a T-septum-ridge SIW is utilized as a transmission-line medium for its constituent modules. Furthermore, in order to allow excitation through conventional RF connectors, a broadband microstrip-to-T-septum-ridge-SIW transition is developed. For practical validation, a 6-GHz SIW TFS prototype featuring 3-dB bandwidth (BW) of 1.1 GHz-i.e., 3-dB fractional bandwidth (FBW) ≈18% — and minimum in-band insertion loss (IL) of 1.28 dB is constructed and characterized. In addition, measured results of a manufactured 5.25-GHz higher-order BPF (two series-cascaded SIW TFSs) with 790-MHz 3-dB BW-i.e., 3-dB FBW ≈15% — and 1.26-dB minimum in-band IL, are also shown.