Design of an X-band symmetrical window bandpass filter based on Substrate Integrated Waveguide

Substrate Integrated Waveguide (SIW) is a new kind of microwave transmission structure appeared in recent years. The SIW technique makes it possible that a complete circuit including planar circuitry, transition, and rectangular waveguide are fabricated in a planar form using a standard printed circuit board (PCB). From analysis of the susceptance of symmetrical window and designing process of Chebyshev bandpass filter in rectangular waveguide, an X-band filter based on SIW is designed and fabricated in this article. The simulated results show that the bandwidth of the filter is 5%. The insertion loss is about 1.4 dB, and return loss is about 25 dB at 10 GHz. The measured insertion and return losses are about 2.9 dB and about 13 dB, respectively at mid-band frequency. The filter has a small insert loss and good frequency selective performances from 9.82GHz to 10.20GHz. It is suitable for designing millimeter-wave circuits, and can be produced with batches to be widely used in the microwave systems with the simple structure.