A novel bandstop filter design with CPW-fed microstrip square loop resonator

A novel microstrip dual-mode bandstop filter with Coplanar Waveguide (CPW) fed structure is proposed by using a microstrip square loop resonator. Two types of coupling between the degenerate modes are described by changing the perturbation´s sizes as in conventional ones. The difference between the proposed filters and conventional ones is resonator fed structures. In the proposed filter design method, CPW-fed structure is used to excite the degenerate modes of the resonator with degenere modes of the square loop resonator. Finally, two dual-mode bandstop filters are designed and realized with using degenerate modes of the microstrip square loop. It is shown that the size of the perturbation element determines the location of the reflection zeros of the filter according to the coupling type of the resonator.