Design and Synthesis of Compact SIW Diplexer with High Isolation

This paper presents the design of a compact substrate integrated waveguide (SIW) diplexer with high isolation. Initially, two high pass filters are designed at desired frequencies and then converted them to bandpass filters using U -shaped slots which are Defected Ground Structures (DGS). For this, the effect of dimensions of the U -shaped DGS structure is studied. The diplexer is finally obtained by combining both the filters using the T-junction power divider technique. To validate the above design ideas, the design is simulated on ANSYS HFSS and a prototype is created. The obtained simulated and measured results are then compared. The simulated insertion losses in the passbands are obtained to be less than 1.25 dB and 1.23 dB at 8.42 GHz and 11.26 GHz respectively while the measured insertion losses are found to be 2.4 dB and 2.2 dB at 8.53 GHz and 11.07 GHz respectively. The return losses of the two filters are found to be better than 26 dB and 35 dB respectively and the isolation obtained between the two filters is better than 30 dB in the desired frequency band.