simulation of microstrip

Hi every body.
I want to simulate a microstrip dielectric resonator filter .
Which simulator is the best one for that structure? HFSS or CST or ADS?
It seems that CST MWS is not a good simulator for this kind of simulation.
I compared CST results with experimentals, they are not matched(for the mentioned structure) .
Dose any body have any suggestion about my problem?
Another problem is that I don't know how to define microstrip ports in CST and HFSS.
I mean what is the optimum size of a microstrip port in CST and HFSS?
The problem is that when the port size becomes large, higher order modes enter the port, and when the port size becomes small, the accuracy of simulation reduces.
What should I do to estimate the optimum port size?
Thank you very much for your assists.

Hi Razavipour,
ADS momentum is the best for filter design.
But I will recommend you another one.
Use Sonnet 11. Its student version is available & you can work up to 2 layers.
I heard that some people have made filters for space application using this software & it worked very nicely.
Try both if you can.