HFSS Multimode Port definition

How o define a multimode port when you don't know which modes are excited?
For example I have a simple waveguide step where the input part is single mode and the other part can support a large number of modes. I have no idea how to define the line of integrations for each of them. Also how HFSS deals with undercut-off modes?

Hi kato01 ,,

Solve for a sufficiently large number of modes.

Integration lines are not required for driven-modal waveports.

Properly. Generally, you will only be able to excite them or view their scattering parameters if they are above cutoff at the port.