how to see impedance of port in cst mws

Hi,
During my simulations, I have found that the line impedance changes with the port size. i want to know their relationship. What should be the values of the port so that line impedance do not change with port size.
Also,do the results, S11 normalised with line impedance or 50 ohms.?
If yes, how can I get S11 with normalised impedance of 50 ohms even when line impedance is not 50 ohms
Surendra

try using discrete port

Discrete ports in my experience never work. What you want to do is make the port just large enough so the magnitude of the fields goes to zero at the boundary. This occurs for microstrip when the horizontal extent of the port is 10 times the line width and the vertical extent is 5 times the height of the dielectric... taken from the 'A Practical Guide to 3D Simulation' from IEEE Microwave Magazine.
Hope this helps,
Lee