Question regarding LF microstrip coupling HFSS

I have a cavity that has two separate microstrip input/output paths (2 in - 2 out) and I want to make sure there is enough isolation between the two RF paths. They are not connected physcially and are not supposed to be coupled to one another.

Currently I'm using a Driven Terminal, Network Analysis model with wave ports at the boundaries. Basically looks like a rectangular waveguide structure with the 2 ends being open like a RWG which I then use a radiation box to contain everything. The microstrip lines feed to the boundary of the radiation box and this is where the waveports are located.

Basically I want to know if frequencies in VHF will produce real results since the entire region and structure is only a few inches in length, width and height.

Thank you

What do you mean by "real results"? Also, is there any particular reason you're using driven terminal?

Usually if you're referring to certain modes, e.g., microstrip modes, you want to use driven modal. The scattering parameters from a driven modal simulation will of course give you the coupling between the lines.