Compact Wideband Dual-Band SIW Bandpass Filters

─ A novel method to design compact wideband dual-band substrate integrated waveguide (SIW) bandpass filters (BPF) is proposed in this paper. By loading a novel beeline compact microstrip resonant cells (BCMRCs) with band-gap characteristics on top layer of SIW, two wide passbands separated by a stopband are generated. In order to enable the filter to have lower reflection coefficients in the two passbands, we use a tapered gradient line embedded with rectangular slots and loaded open stubs as the transition structure from microstrip line to SIW. The wideband dual-band BPF (DBBPF) is fabricated. The lower-band and upper-band fractional 3-dB bandwidths are 58.2% and 22.6%, while the measured minimum insertion losses (ILs) are 0.7 and 0.92 dB, respectively. The stepped-impedance openloop ring resonator (SIOLRR) is introduced in order to improve the selectivity of the filter. The wideband DBBPF with SIOLRR is studied, simulated and measured. Two transmission zeros are generated in the stop band between the two passbands. Good agreement between simulated and measured results can be obtained. Index Terms ─ Complementary split ring resonators, defected ground structure, dual-band bandpass filter, stepped-impedance open-loop ring resonator, substrate integrated waveguide.