Waveport excitation for dielectric waveguide in HFSS

u can use a plane wave excitation in HFSS

I am trying to work with plane wave excitations in HFSS, but I have having some problems.

I can set up the plane wave itself.

I am having problems figuring out how to recover the S-parameters produced by the plane wave excitation. There does not seem to be a port type meant to work specifically with plane waves.

I could use waveports, but I have found that the S11 response of the dominant mode varies based on the number of modes I specify. This does not make sense to me, but that is what happens in my simulation.