Diffraction of an electromagnetic beam by infinite planar periodic metal-strip grating

An hybrid angular spectrum method-Galerkin moment procedure has been developed to analyze the diffraction of an electromagnetic beam incident obliquely on an infinite planar periodic metal-strip grating. The integral expression obtained for the scattered field is expanded by means of an asymptotic method for determining the diffracted far-field. Some numerical examples show the decomposition of the incident beam in several beams corresponding to the propagating Floquet harmonics excited in the grating. The propagation directions of these beams show deviations with respect to the directions predicted by the Floquet theorem. The profile of the scattered far-field is analyzed as a function of the geometrical and electrical parameters