Novel dual-mode bandpass filters using substrate integrated waveguide cavity structure

This article proposes dual-mode balanced bandpass filters (BPFs) with high common-mode (CM) rejection performance using the substrate integrated waveguide (SIW) cavity and its size-reduced form, a folded SIW cavity structure. The latter's size (folded cavity) is nearly 50% of the former. The passband response of the proposed dual-mode balanced BPFs are formed by the (folded) SIW cavities' two degenerated modes, TE102 and TE201 modes. The advantages of the proposed BPFs are higher Q value and higher power handling capability as compared with those of the microstrip counterparts. The dual-mode resonance of the SIW cavity also offers the benefit of size reduction and, sometimes, higher Q value than that of its fundamental mode. The hybrid microstrip/slot is used to design the filters' feed structure for enhancing the CM rejection. This high CM rejection is caused by the noncoupling nature of the slot, which bisected by an imposed perfect magnetic wall. The measured in-band CM rejection levels are around 40 dB with the differential-mode insertion losses around 2.5 dB. (c) 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:402-406, 2016