Displaying Vector Field

I was wondering if anyone could help me with a problem I am having in Ansoft HFSS 11. I am modeling an h-plane T waveguide, and want to place a plane dissecting the model in half which I could plot a vector field on. I know how to plot vector fields by selecting the face and selecting the vector button, but I want to know if you can just place planes anywhere in your model and plot the vector field normal to them. I would be exciting the wave port with vertically polarized waves so the field will be normal regardless.

Also, one more thing, how does ansoft know which port the indent wave enters? Is it just the first port that you create? Or is there a way to select it in the excitations somehow? I noticed it has to choose a port because running the animation shows the wave entering at a particular location, or are all ports analyzed to be excited and you can pick out the incident location in the animation option? Thanks in advance.