Re: Help with Waveports
You shouldn't use the whole face of the vacuum box. Draw a rectangle on the surface of the box, taking up part not all of the face, and use that rectangle as the waveport.
By doing so you can make the waveport include one wire but not the other. However, you have to be careful about how big to make the waveport. The fields from any wire extent to infinity but the waveport does not, so a waveport exciting a wire will always be at least slightly imprecise. If your wires are close enough to significantly couple with each other, then the fields are significant throughout the space between the wires - but if you want the waveport to touch only one wire, it cannot enclose all that space, so the results will be significantly inaccurate. This is a dilemma, but I think the way to solve it is to start the wires far apart from each other where there's little coupling, then bring them closer and run them parallel for a while, then separate them again before they reach the waveport(s) at the other end. I suspect the coupling will then vary significantly based on the length over which coupling is significant (i.e. how many times the wavelength) - try it and see. Of course in real life, coupling lengths are finite not infinite, so use the actual length if you know it.
Note: I'm not 100% sure about the previous paragraph, if I'm wrong somebody please point it out.
In addition to lumped ports, and waveports as I described them, HFSS also has a "driven terminal mode" which seems like it might be what you want here.