tem waveguide hfss
I have used waveguide port extensively in my simulations. The trick is to get the TEM modes of the waveguide to couple to the MS-line or a similar waveguide.
Here is what I do:
I draw the MS line (XY plane, X directed) on the substrate as a PEC boundary, and the ground plane (also a PEC boundary)
Then I draw a copper cube touching one end of the MS line. Size of this is about 3 times the width (Y) of the MS-line, height (Z) about the 3 times the MS line width but the thickness (x) is truvial. (I'll tell you how to optimize this)
The face of the copper cube touching MS line and the substrate is now selected to define a waveguide port.
Optimizing the Port Size
Before going for full simulation, you may do port simulation only. Have a look at the field patterns on the port. They should look like those of a MS-line and should be nicely contrained within the port. If not there can be errors in coupling.
Hope this helps.