K-band backward diplexer in substrate integrated waveguide technology

The first backward diplexer for K-band substrate integrated waveguide (SIW) operation is presented. The advantage of this compact diplexer is having input and two output port interfaces at the same side of the substrate, which advances the applications of SIWs to more complex feed system assemblies. The diplexer has two bands at 20 and 21 GHz. The bandwidth of each band is 0.4 GHz, which gives 2 and 1.9% bandwidth at lower and higher bands, respectively. The diplexer is designed and analysed with the mode-matching technique, and its performance is verified by comparison with simulated and measured data. The in-band measured return and insertion losses are 14.65 dB/2.75 dB in the lower band and 13 dB/3.05 dB in the upper band.