Transmission Zeros in Rectangular Waveguide Filters: A Novel Approach for Generating the Source-to-Load Coupling

In this paper, a new inline configuration of rectangular waveguide filter is presented for source to load (S-L) coupling to generate transmission zeros (TZs). The S-L coupling in the inline configuration is realized by a waveguide section with small cross-section. In contrast to the folded structure, in an inline configuration input and output are distant as they are at the opposite side of the filter. This results in a long waveguide line connecting input and output that behaves as an overmoded cavity generating several spurious frequencies. In this paper, a method for the suppression of such resonances is presented. In order to demonstrate the feasibility of the proposed approach, a 4th order waveguide filter centered at 9.55 GHz having F.B.W of 3.2%, 2 TZs, and suppressed resonances generated by S-L coupling resonator is designed. Analysis of both equivalent circuit and EM simulation is presented.