Create a circle that has the diameter of the thickness of your torus, then, perpindicular to it, create another circle which defines the diameter of the torus. Then sweep the first circle along the second.
I believe you need to have at least 3 cells worth of distance where the material is the same as the cross section of the port. In general, you should have a good length (maybe 1/8th lamda?)of waveguide between your port and any discontinuities, then de-embed (change the reference plane) back...
