Ultra-wideband combline filters based on miniaturized engineered resonators and inter-resonator tapped-in coupling

New designs of UWB combline filters based on miniaturized engineered resonators are presented. The problem faced in those designs of how to realize the strong coupling required in UWB filters is solved by using inter-resonator tapped-in coupling method previously introduced in [2]. Optimization of coupling is straightforward; design is less sensitive to the parameters of tapped-in coupling as compared to conventional coupling. Beside simplicity, such a solution is valuable in practice as it does not require any change or adjustment in current fabrication technologies. As a proof of concept, the designs of cavity combline filters are taking into account practical implementation in multilayer technology. Fabrication in other technologies is also applicable. The four-pole filters presented in this work have relative BW of 77.5% and electrical size of λ/5 × λ/5 × λ/55.