what is perfect H in hfss

hi
what is perfect H (physically) in hfss?
and when i choose guid with 2 sides (perfectE) and 2 sides (perfect H) i obtain guid TEM!

thanks

Perfect H is a perfect magnetic boundary. It causes the magnetic field (H-field) to be in a direction normal to the surface that it is assigned to.
The perfect H boundary forces the tangential component of the H-field to be the same on both sides of the boundary. For internal planes, this results in a natural boundary through which the field propagates. For planes on the outer surface of the model, this results in a boundary that simulates a perfect magnetic conductor (the tangential component of the Hfield is zero).

////////thank you