Design of elliptic-function microstrip filters with defected ground structures

In this study, a design procedure which includes three steps is proposed to improve the frequency characteristics of elliptic function microstrip filters with defected ground structures. Firstly, a conventional filter design is presented using elliptic filter prototype. Following the first step, normalized element values of elliptic low pass filter prototype are used and desired filter transformation is carried out. Secondly, microstrip filter transformation of obtained elliptic low pass filter is attained. Lastly, ground plane is etched with different shapes like square-dumbbell, interdigital and fractal versions of different geometries. In this case, an improvement of microstrip filter design is achieved using Defected Ground Structures (DGSs). MATLAB and full wave electromagnetic simulators are used to model the proposed filters. Scattering parameters of microstrip elliptic filter are extracted and plotted via commercial EM design environments. Modifications of ground plane with different geometries are applied to the microstrip elliptic filter via EM software tools and consistent simulation results are obtained.