urgent plz!!!

i m simulatin a CPW antenna without groundplane. I am using CST 2006B as the tool. I define the waveguide port to excite the model. The line impedance shown in the 2D results isnt accurate. Any suggestions how to excite the model with 50 ohm waveguide port whatever the stripline impedance is??

would you please upload your design? It is easier then to suggest something.