Let's say, we have a rectangular waveguide, with one end shorted, and the other end with absorbing boundary, in the middle of the waveguide, we have a incident plane wave excitation. So how should we model this incident plane wave excitation numerically? by equivalent surface magnetic current density? or use a total = incident + scattering fields decomposition, with the total field solved on the side of shorted end and scattered field on the open end ? I did not get reasonable results either way, so I guess I may make some mistakes when modeling this excitation. Thanks in advance for your kind help!