Pseudoelliptic microwave bandpass filters with three transmission zeros in quadruplet topology with frequency-dependent couplings

This paper discusses the properties of microwave bandpass filters with three finite transmission zeros realized in the quadruplet topology with frequency-dependent couplings. Firstly, the advantages of introducing dispersive couplings into a quartet section are discussed in terms of the number of realizable transmission zeros. Next, the sensitivity of filters characteristics with three transmission zeros (in terms of perturbed couplings) with constant and dispersive couplings are presented. Finally, two examples of a waveguide X band quadruplet with three transmission zeros implemented using dispersive direct and crosscoupling are presented to prove theoretical considerations.