Substrate-Integrated Waveguide Dual-Mode Dual-Band Bandpass Filters With Widely Controllable Bandwidth Ratios

A realization method, named the design parameters ratio technique, of substrate-integrated waveguide (SIW) dualmode dual-band bandpass filters (DM-DBBPFs) with widely controllable bandwidth ratios is presented when TE101 and TE201 modes in substrate-integrated rectangular cavities are exploited to dominate the first and second passbands, respectively. Emphasis is placed on filters design to simultaneously realize the design parameters including the external quality factors Q(e) and coupling coefficients M-ij required for both passbands by determining proper offset positions of the feeding ports and coupling windows, which can easily be fixed by ratios of synthesized Q(e) and M-ij for the two bands, respectively. Consequently, the fractional bandwidths (FBWs) of the two passbands can be allocated flexibly over a wide range of ratios, typically with the FBW ratio of 0.2-1.5. Three SIW DM-DBBPFs including a third order direct-coupled one operating at 12 and 16 GHz with the identical absolute bandwidths, a third-order cross-coupled one operating at 12 and 15 GHz with the same FBWs, and a fourth order cross-coupled one operating at 12 and 17 GHz with the FBW ratio of 0.6 are designed and fabricated to demonstrate the method.