Design of Miniaturized Hybrid-Electromagnetic Cross-Coupled Bandpass Filter

To meet the requirements of wireless system on high selectivity and miniaturization, a filter topology based on hybrid-electromagnetic cross-coupling is proposed in this paper. Differing from the traditional third-order filter which can only produce one transmission zero through using cross-coupling, the proposed hybrid-electromagnetic cross-coupled topology can introduce two transmission zeros on both sides of the passband, then greatly improves the selectivity of the low-order filter. Thus, a design scheme for miniaturized high selectivity filter can be achieved. Based on this topology, a third-order filter based on microstrip quarter-wavelength resonators is designed to verify the principle of transmission zeros generated by this topology. Then, in order to obtain wider bandwidth, a hybrid microstrip/slot-line resonator filter is designed. This structure can achieve larger coupling coefficient and larger bandwidth with a miniaturized size.