Right port dimensions for microstrip line in CST， time doman

Hi!
What dimensions should have a port for a 50Ohm microstripline (1.1mm width and 8mm length) on a 0.5mm thick Rogers 4003 substrate (Er=3.55, tandelta=0.0027) for CST time dom. simulation for freq 0-40 GHz? It is something wrong width my s21 insertion loss - much more than that of the same line simulated in ADS and in HFSS.
Can somebody help me?
Thanks

In CST u can calculate it by using Macros->Calculate
U can also use utility like AppCAD to calculate the impedance
http://www.hp.woodshot.com/appcad/appcad.htm