function s = ground(si,typ,diel,cond,nrad,rrad,drad)
% s = ground(si,typ,diel,cond,nrad,rrad,drad)
% Adding ground parameters to the antenna model 
% si   :  data structure of the antenna model
% typ  :  I1 of GN-Card
% diel :  F1 of GN-Card
% cond :  F2 of GN-Card
% nrad :  I2 of GN-Card   number of wire radials
% rrad :  F3 of GN-Card   length of radials
% drad :  2*F4 of GN-Card diameter of radial wires  
% s    :  data structure of antenna model including ground effects 
