In this article, a simple single-layer substrate integrated waveguide diplexer is proposed in which a dual mode cavity is used as a junction. A square substrate integrated waveguide cavity with corner cut perturbation is as the dual mode cavity and the odd and even modes of this cavity are a part of the receiver and transmitter channel filters, respectively. These two modes are coupled to the other sections of the receiver and transmitter filters in such a way that the designed receiver and transmitter filters are independent from each other. The diplexer coupling diagram is studied and characteristic polynomials of the diplexer are obtained based on the characteristic polynomials of receiver and transmitter channel filters. The proposed diplexer provides high isolation between two passbands and also has a compact size; therefore, it can be suitable as a section of a system on substrate. A prototype diplexer is fabricated by a printed circuit board process on a single layer. Design process and simulated and measured results of the fabricated diplexer are presented.

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