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Abstract
A new type of dual-mode planar filter with flexible transmission zeros using slot-line square loop resonator (SSLR) is presented. This resonator is based on the slot-line loop on the ground plane. Four slot-line stepped impedance stubs are loaded in the center loop to achieve compact size and harmonic suppression. Two sizes of slot patches added at the inner corners can split the degenerate modes and adjust the coupling between even and odd modes. A pair of T-shaped feed lines on the top plane can provide flexible source–load coupling, which leads to symmetrical or asymmetrical frequency response. Both the equivalent circuit and coupling matrix analysis methods are utilized to design the dual-mode filter. Two kinds of filters operating at 3.35 and 3.80 GHz with wideband and flexible transmission zeros are designed and fabricated.
Acknowledgment
This work was supported by the National Natural Science Foundation of China (NSFC) No. 60901031 and the Fundamental Research Funds for the Central Universities No. 72005477.