A novel compact diplexer employing substrate integrated waveguide loaded by triangular slots for C-band application

This article presents a novel design of compact Substrate Integrated Waveguide (SIW) filters loaded with a triangular slot. First, the filtering response is obtained by loading a triangular slot on the top of the SIW cavities. Later, these SIW filter structures are cascaded to develop a SIW planar diplexer. To achieve lower and upper channels of the diplexer, two SIW cavity-backed filters loaded with triangular slots are excited with in-line feedings. To demonstrate the analysis, the proposed SIW diplexer has been simulated, fabricated, and tested. The measured S-parameters are in good agreement with the simulated results, showing the lower and upper passband insertion losses based at 6.2 GHz and 7.75 GHz are obtained as 0.87 dB and 0.75 dB including the losses from both the SMA connectors, respectively. The fractional bandwidth (FBW) is more than 5.1% at each passband with high isolation better than 22 dB. The fabricated prototype has a compact size of 0.88 ( $ \lambda _g^2 $ λg2).