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 TE
₁₀₁
and TE
₂₀₁
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 thirdorder 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.