Hopefully a simple question. When adding a "box" around a layout, does momentum treat the inserting portion of a conductor and the side wall as being grounded?
If you have a top or bottom ground plane, then the box side walls will be at the same, ground potential. So if other strip layer objects touch the side wall, they should also be grounded.
How do i then model in my specific case a filter inside a metallic case?
Ports have to be placed on the box line, otherwise i get an error message and cannot start simulation. But when i do, the end of the feedlines touch the box and are therefore grounded.
No, the ends of ports are special. Think of them as an infinitesimal gap across which a source is applied. However, boxes in Momentum cause a lot of resonance effects that are normally not desired, so I would generally try to simulate structures with top, bottom and side walls (waveguide) only.
Ports have to be placed on the box line, otherwise i get an error message and cannot start simulation. But when i do, the end of the feedlines touch the box and are therefore grounded.