Miniaturized Diplexers With Large Frequency Ratios Based on Common Half-Mode Dual-Mode SIW Junction-Cavities

Miniaturized substrate integrated waveguide (SIW) diplexers with widely separated channel passbands using common half-mode dual-mode SIW junction-cavities are presented and developed for 5G sub-6 GHz communications and wireless systems. With this kind of half-mode dual-mode junction-cavities to eliminate the conventional T-junctions and also to produce one transmission pole in each channel passband, significant circuit miniaturization can be achieved for SIW diplexers. Additionally, by exploiting the first dual modes in the half-mode SIW junction- cavities, flexibly allocated fractional bandwidths (FBWs) for the two channels can be realized through FBW design graphs, large frequency ratios can also be accommodated, which is difficult to implement using the whole-mode SIW cavity scheme due to spurious problems. Two compact SIW diplexers with large frequency ratios are synthesized, designed, fabricated, and measured for demonstration, including a third-order direct-coupled prototype centered at 3.5 and 5.0 GHz with a frequency ratio of 1.43 based on the TE₁₀₁/TE₃₀₁ half-mode dual-mode junction-cavity and a fourth-order cross-coupled prototype centered at 3.5 and 5.5 GHz with a frequency ratio of 1.57 based on the TE₁₀₁/TE₁₀₂ half-mode dual-mode junction-cavity.