The following requirements must be satisfied in any wave port application.
Wave ports are typically applied on the structure boundary. In some circumstances, wave ports may also be applied to internal faces and edges, as explained in Internal Wave Ports on Traces and Internal Wave Ports on Waveguides.
Wave ports of the same index (or index magnitude, as in differential ports) must be coplanar, as they are considered a single port. In addition, they must not be electrically isolated from each other.
A differential port must have exactly one positive terminal, though it may have any number of negative terminals.
If you have several coplanar wave ports, they must either all have the same index magnitude (example: 1, -1, -1, these will be considered one port), or all have different index magnitudes (example: 1, 2, 3, considered separate ports). The combination of several indices with the same magnitude with one or more indices of different magnitudes is not permitted (example: 1, -1, 2 is not supported.) Note that this restriction does not apply to lumped ports.
The wave port plane cannot be entirely made up of good electrical conductors.
Any symmetry planes in your geometry must bisect the wave port.