cst waveguide port definition

Hi, folks,
How should I properly define the dimension of a waveguide port for coplanar waveguide structure? The HELP suggests a "5 times wide of center strip"X"3 times height of substrate". However, large ripple occurred on my S-parameter curve due to the transient signal not decayed to zero after simulation runs. And I've setup the accuracy to -40dB. Is there anything else I haven't taken into account?
Thank you very much for you guys' help!
Kindest Regards,
Chunwei

Hi,
It could mean a lot of things. In my opinion, one of your setting are incorrect for the structure. Can you be more specific about your design or post it in this forum?
P.