Design of a compact SIW diplexer with square cavities for C-band applications

In this paper, a novel design of compact substrate integrated waveguide (SIW) diplexer with square cavities for C-band applications is presented. This diplexer is working on evanescent-mode propagation and operating below the cut-off frequency of the cavity. First, the filtering response of triangular-slot loaded on one square cavity surface is investigated. This response of the cavity is then applied on two cascaded filters to obtain the diplexer characteristics. To validate the concept, a narrow band filter and diplexer are designed and simulated. The insertion losses at lower and upper passbands centered at 6.16 GHz and 7.72 GHz are obtained as 0.83 dB and 0.77 dB, respectively. The proposed diplexer provides a fractional bandwidth more than 5.1% at each passband with high isolation better than 22 dB. These features show that the proposed diplexer is a suitable candidate for C-band application