The Circular Port Reference Axis is available only in 3D. When the Type of port is set to Circular under Port Properties, the Circular Port Reference Axis subnode is available from the context menu (right-click the Port parent node) or from the Physics toolbar, Attributes menu. Two points are used to define the orientation of fields on a port boundary. If there are more than two points on the selection list, the first and last points are used. For the fundamental TE11 mode, the direction of the reference axis corresponds to the polarization of the electric field at the port center.