A novel compact dual-band bandpass waveguide filter is presented in this paper. H-plane metal inserts with complementary split-ring resonators are implemented as resonating elements in the standard (WR-90) rectangular waveguide. Design starts from the models of the waveguide resonators with two resonant frequencies (9[Formula: see text]GHz and 11[Formula: see text]GHz) using a single flat or folded metal insert. Further, folded inserts are used for the second-order dual-band filter design. The equivalent circuits are proposed for the considered waveguide resonators and filter. A good agreement of the amplitude responses obtained for three-dimensional electromagnetic models and microwave circuits is achieved. Finally, compact dual-band bandpass waveguide filter is proposed as a novel solution using miniaturized inverters for both central frequencies. Compact filter model is further modified in order to obtain solution customized for easier fabrication. For the compact filter model, amplitude response is experimentally verified. The required filter response is preserved, as verified by a good agreement of the results obtained for the original dual-band filter and for the compact filter solutions.

A novel design of second-order dual-band H-plane bandpass waveguide filter is presented in this paper. Filter design is relatively simple and is based on the use of complementary split ring resonators, implemented as metal septa, with properly shaped slots, in the transverse planes of the standard (WR-90) rectangular waveguide. The positions of the resonators on the same septum are chosen in such a manner that there is no mutual coupling between them. This approach is used for the design of the waveguide resonator with two resonant frequencies (9 GHz and 11 GHz). Further, the second-order dual-band bandpass waveguide filter, with symmetrically positioned folded septa, is presented. The equivalent circuits of the considered resonators and filters are developed. The proposed dual-band bandpass filter design is verified by a good agreement of the filter responses obtained for three-dimensional electromagnetic models and equivalent microwave circuits. Finally, the method for filter miniaturization is introduced and applied to the second-order dual-band filter. The required filter response is preserved. Keywords-bandpass waveguide filter; complementary split ring resonator; dual-band bandpass filter; miniaturizationI.