An aperture boundary can only be assigned on a 2D sheet object assigned as IE Region. These objects will be meshed as part of the solution process.

To create an aperture boundary in HFSS:

1. Create a 2D sheet object on the XY plane at the elevation of ground plane.
2. Select the object and right-click Assign Hybrid>IE Region.
2. Select the object and right-click Boundaries>Assign>Aperture to display the Aperture dialog.

3. Type the boundary's name in the Name text box or accept the default name. (To change the default base name to one of your choosing, see Setting Default Boundary/Excitation Base Names.)