Coplanar-Waveguide Fed Microstrip Dual- Band Bandstop Filters with Inductively Coupled Dual-Mode Ring Resonators

This paper presents a novel microstrip dual-band bandstop filter design by using inductively coupled Coplanar Waveguide fed (CPW) dual-mode resonators. Two nested dual-mode square loop resonators with perturbation elements on microstrip layer are constructed to produce first and second band. In the proposed filter design method, inductively coupled CPW rectangular rings are used to excite the degenerate modes of the resonators to obtain dual band bandstop filtering structure. Two perturbation elements are used to control the reflection zeros of the first and second band. So, two different filter responses are obtained by repositioning the reflection zeros. Charge distributions of the reflection zeros and poles of the structure are investigated for each stopband to exhibit the mode characteristic. Two filters are simulated with a full-wave EM simulator. Two filters are implemented and measured. Despite the production losses are high as a result of the CPW-fed structure, the measurement results are in good agreement with the simulation results.