A New Design Method of Microstrip Dual-Band Bandstop Filters

A generic lumped-element circuit of dual-band bandstop filter (DBBSF) is proposed based on novel composite shunt resonators, and its design method is developed with closed-form formulas. As an example, a DBBSF with center frequencies of 1.7 and 2.3GHz is designed and fabricated using microstrip lines. The measured frequency response agrees excellently with the theoretical predictions, validating well the proposed design theory and filter structure. II. DESIGN METHOD OF DBBSF We provide first the design formulas of a conventional bandstop filter. Fig.1 shows a generic circuit of an n-degree BSF using conventional series LC resonators and admittance inverters. The parameters, including the inductor Lri, capacitor Cri, and admittance-inverter Ji,i+1 are related by the following well-known formulas . Index Terms — Bandstop filter, dual-band, composite shunt resonator, microstrip line