defected ground structures in patch antenna

hi all
i want to know how to make equivalent circuits of DGS for patch antennas
Give me circuits for ( example when DGS is a rectangle or circle shape)
any reference papers
regards kartik

Getting good material on this topic is difficult..! I tried to find good material and couldn''t..! There are some Power points by agilent were some examples are taken and modelled in ADS..! U'L find them in Google..!