Filter design using Defected Ground Structures and Defected Micro-strip Structures.

Hi,

I am trying to use DGS and DMS to design elliptic filters on micro-strip line. But, it is giving a lot of problems like mutual coupling between two DGS, the impedance and S-parameter characteristics change when DGS is shifted on a microstrip line et al.. This is not enabling me to make a proper design of the filter needed. Also is there any proper design procedure for a DGS loaded Low-Pass filter. If so please let me know, as DGS from what i have learnt and simulated till now is an arbitrary structure. A proper design approach is not available anywhere. Any help would be greatly appreciated.

Thank You!