Songbai Zhang; Lei Zhu; Weerasekera, R., "Synthesis of Inline Mixed Coupled Quasi-Elliptic Bandpass Filters Based on \lambda /4 Resonators," in Microwave Theory and Techniques, IEEE Transactions on , vol.63, no.10, pp.3487-3493, Oct. 2015 doi: 10.1109/TMTT.2015.2467380
Abstract:
This paper proposes a general synthesis method for inline mixed coupled quasi-elliptic band pass filters based on λ/4 resonators. Different from the conventional modeling with lumped and mixed inductive and capacitive coupling, the proposed mixed coupling model here includes not only the coupling magnitudes,
but also their paths’ phases inside the mixed coupling. According to the presented formulation, there exists one lower side transmission zero for the capacitive-dominant mixed coupling. However, there are two transmission zeros in the upper stopband for the inductive-dominant case, and these two transmission zeros can be analytically synthesized with different coupling path ratios. The proposed synthesis method is then applied to design two second-order bandpass filters based on inductive-dominant λ/4 coupled resonators,
resulting in two upper stopband transmission zeros. Furthermore, this synthesis method is extended to design two fourthorder quasi-elliptic bandpass filters with both inline capacitive and inductive-dominant mixed couplings. Finally, the designed filters are fabricated and measured to provide successful verification
on the proposed mixed coupling model approach.
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