Multichannel Substrate Integrated Waveguide Diplexers Based on Orthogonal Dual Modes and Split-Type Multiband Responses

An approach for implementing compact multichannel substrate integrated waveguide (SIW) diplexers is presented based on orthogonal dual modes and split-type multiband responses. By coupling multiple TE
₁₀₁
-based bandstop single-mode cavities to TE
₂₀₁
/TE
₁₀₂
-based bandpass dual-mode cavities, one or both of the two passbands constructed by TE
₂₀₁
and TE
₁₀₂
modes could be split into multiple subpassbands. Additionally, by arranging two output ports at central positions of adjacent sides of the last cascaded dual-mode cavity, isolations between these two output ports can be achieved and then further improved by tiny offset locations benefitting from the orthogonal characteristics of TE
₂₀₁
and TE
₁₀₂
modes. Three experimental prototypes, including a 1 + 2 type tri-channel SIW diplexer, a 3 + 1 type quad-channel SIW diplexer, and a 2 + 2 type quad-channel SIW diplexer, are synthesized, designed, fabricated, and measured to demonstrate and validate the proposed mode-collaborative design concepts.