Substrate-Integrated Waveguide Dual-Band Filters With Closely Spaced Passbands and Flexibly Allocated Bandwidths

Substrate-integrated waveguide (SIW) dual-band bandpass filters (BPFs) with closely spaced passbands and flexibly allocated bandwidths are presented based on TE
₁₀₂
and TE
₂₀₁
modes in substrate-integrated rectangular cavities (SIRCs). The constraint relationship among the first four mode resonances in an SIRC with its aspect ratio is theoretically analyzed first to explore the realizable frequency ratio of TE102 and TE201 modes. The fractional bandwidth (FBW) design graphs are also delineated to demonstrate the available FBWs of the two passbands. Two SIW dual-band BPFs, including a third-order direct-coupled one centered at 20 and 22 GHz with respective FBWs of 2.6% and 3.9%, and a fourth-order cross-coupled one centered at 20 and 21.5 GHz with both FBWs of 2.35%, are designed, fabricated, and tested for demonstration, showing good agreement between the simulation and measured results.