The attachment is a tutorial about port selection in HFSS.The use of wave ports as internal ports is described at page7.Two questions I would like to ask are:
How shoud I create a conducting cap?Just do it like other solid model?
How large the cap should be?
Re: How to create cap requred by wave ports as internal port
Create a solid with one face against the "back" of the port. The cap could be larger than the port if that made sense in your simulation. The excitation will emerge from the other side of the port. Assign the solid as PEC. I usually make the cap the same size as the port and (usually) very thin although there are situations where a long element is better. It depends on what you want to model,