Abstract-A novel miniaturized dual-band bandstop filter (DBBSF) is proposed by using the T-shaped defected microstrip structures (DMSs) and the U-shaped defected ground structures (DGSs) in this paper. The layout of the dual-band bandstop resonator (DBBSR) is presented at first. The dual stopbands of the DBBSR can be separately controlled since the mutual coupling of the defected structures is negligible. The working principles of the T-shaped DMS and U-shaped DGS are then provided and their design process is summarized. On the basis of the DBBSR, the design methodology of the compact DBBSF is proposed before its design procedures are presented. Following the design procedures, a second-order and thirdorder DBBSFs with Butterworth frequency response are designed, simulated and fabricated. The equivalent circuit models of the designed filters are also developed. Full-wave simulation results of the fabricated DBBSFs are in good agreement with the circuit simulation and measurement results, validating our proposed design methodology.

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A cascaded trisection substrate-integrated waveguide bandpass filter with better frequency selectivity is presented. The proposed coupling scheme can be divided into two trisection topologies. By changing the signs of coupling coefficients between cascaded resonators, two transmission zeros can be simultaneously placed at the higher or lower stopband, or one can be located below and the other above the passband. A filter sample is designed and fabricated with standard single-layer printed circuit board technology. The measured S-parameters agree well with the simulated counterparts, and good performance of the filter is predicted.

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