Novel Microstrip Bandstop Filters With Controllable Dual Stopbands

This paper reports a novel bandstop filter featuring two controllable stopbands at desired frequencies. Stepped- impedance resonators are utilized in filter design to obtain dual- stopband characteristics and size reduction. The synthesis method is well developed and the design curves are given. Two experimental circuits are fabricated and measured to validate the design concept. Measurement results agree well with the simulation results. As compared with an ordinary DBBSF, the proposed filters can achieve more than 12% size reduction.