The diffraction of a non uniform plane electromagnetic wave by the er(Se of
a electrically perfectly conducting half plane in a bi-anisotropic media i
s rigorously analysed. The high-frequency asymptotic expansion reveals the
existence of a coupling effect between a transverse magnetic (or transverse
electric) incident plane wave and the transverse electric (or tranverse ma
gnetic) slope-diffracted field. A numerical verification using the Mathemat
ica sofware is presented.