Mode Matching design of substrate integrated waveguide diplexers

A K-band diplexer based on Substrate Integrated Waveguide (SIW) technology is presented. The diplexer has input and output ports on opposite sides and bandwidths of 2.75 percent and 2.11 percent at 18.15 GHz and 19 GHz, respectively. The diplexer is designed using an efficient Mode-Matching Technique (MMT), verified by CST and prototyped. Measured results are in good agreement with theory and simulation results and show good isolation between the channels. Attenuation towards higher frequencies is better than 40 dB up to 25 GHz. The measured insertion losses are 3.05 dB in the lower band and 2.3 dB in the upper band.