50 ohm ohne tastkopf

hii
plz tell me how can a define and create 50 ohm coaxial probe for exciting the antenna in FDTD?
plz tell me the exact alogorithm for creating cylinder in MATLAB.

i tried for defining cylindrical object in MATLAB but i don't where is the problem.
here i am giving matlab code plz tell me where is the problem...........

%Define cylinder
cylinder(1).radius = 1e-3;
cylinder(1).height = 17e-3;
cylinder(1).centre_x = 0.5e-3;
cylinder(1).centre_y = 7.125e-3;
cylinder(1).centre_z = 1e-3;
cylinder(1).material_type = 2;


% create cylinder
disp('creating cylinder');

cx = fdtd_domain.cell_center_coordinates_x;
cy = fdtd_domain.cell_center_coordinates_y;
cz = fdtd_domain.cell_center_coordinates_z;

for ind=1:number_of_cylinder
% distance of the centers of the cells from the center of the sphere
distance = sqrt((cylinder(ind).center_x - cx).^2 ...
+ (cylinder(ind).center_y - cy).^2);
I = find(distance<=cylinder(ind).radius&&(abs(cylinder (ind).height-cz)<=cylinder.height/2);
material_3d_space(I) = cylinder(ind).material_type;
end
clear cx cy cz;

Do not create a cylnder model with boxcells.
Use CST instead.

i want to do this using FDTD by making program in MATLAB.
i have done this using CST MWS nd HFSS but i want to do this using FDTD method.

ithink this paper will help u