The Diffraction Order port is available in 3D and 2D. When the Type of Port is set to Periodic under Port Properties, this subnode is available from the context menu (right-click the Port parent node) or from the Physics toolbar, Attributes menu.

Use the Diffraction Order port to define diffraction orders from a periodic structure. Normally a Diffraction Order node is added automatically during the Periodic port setup. Additional Diffraction Order ports subnodes are available from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.

Enter a unique Port name. Only nonnegative integer numbers can be used as Port name as it is used to define the elements of the S-parameter matrix and numeric port names are also required for port sweeps and Touchstone file export.

Select the Components setting for the port — In-plane vector (the default) or Out-of-plane vector.

Specify an integer constant or an integer parameter expression for the Diffraction order m (the default is 0) and in 3D n (the default is 0).

Note that In-plane vector and Out-of-plane vector are based on the plane of diffraction which is constructed with the diffraction wave vector and the outward normal vector of the port boundary. The diffraction wave vector is defined by

where m and n are diffraction orders, k ≥ kdiffraction,parallel, k is the magnitude of the wave vector and kdiffraction,parallel is the magnitude of kdiffraction,parallel. The reciprocal lattice vectors, G1 and G2 are defined from Periodic Port Reference Point.

In-plane vector lies on the plane of diffraction while Out-of-plane vector is normal to the plane of diffraction.

For a 2D component, In-plane vector is available when the settings for the physics interface is set to either In-plane vector or Three-component vector under Components. Out-of-plane vector is available when the settings for the physics interface is set to either Out-of-plane vector or Three-component vector under Components.

where n is the port boundary normal and z is the unit vector in the out-of-plane direction. Since the normal n points in opposite directions for the exciting port boundary and the transmission side port boundary, G1 will point in different directions on the two opposing port boundaries. Thereby, also the mode numbers for the two port boundaries will be different. For example, mode m = 1 on the excitation side, corresponds to mode m = -1 on the transmission side.

Enter a value or expression for the Mode phase θin (SI unit: rad). The default is 0 radians. The Mode phase setting is further discussed for the Port feature.