Analytical Synthesize and Dimensioning of FDC Waveguide Filters

By treating Frequency Dependent Couplings (FDC) as a unique element, this paper presents an analytical synthesis and implementation approach using a circuit-based method. The derived prototype can realize filter functions with up to N-1 predefined finite frequency transmission zeros
$(\mathrm{N}$
being the filter order). This method is directly applicable without the need for intermediate circuits, iterations, or optimization procedures. Equations related to the de-normalization process involving FDC in dimensioning are provided. A five-pole waveguide filter with all FDC inter-resonator couplings is analytically designed without any global optimization. Simulation and measurement results validate the efficiency and accuracy of the proposed method.