Design of Dual-Band Bandstop Filters Using Microstrip and DGS Resonators

In this paper, we present a dual-band bandstop filter(DBBSF) design using quarter-wavelength resonators and defected ground structures(DGSs). The quarter-wavelength resonators on the upper plane contributes the lower stop band, and the open-loop DGS resonators on the ground plane introduce the higher stop band. And a reasonable tuning method is adopted to tune the two stop-bands with smooth responses. The design strategies and the equivalent circuits are introduced in detail. A third-order dual-band BSF with center frequencies of 0.55GHz and 1.05GHz is designed and fabricated. The attenuation of the filter greater than 20dB for the two stop-bands. Good agreement is achieved between the experimental results and the simulation results.