Scattering of an arbitrary wave by a thin strip grating reflector

A simple approximation method to calculate scattering from a thin strip grating of a finite size is proposed for arbitrarily polarised incidence with an arbitrary plane of incidence. First, the grating is projected on the plane normal to the direction of incidence. The grating parameters are transformed at the same time according to a simple rule. Then, reflection and transmission coefficients for a plane wave are readily calculated for the fictitious problem of normal incidence on the projected grating. Equivalent electric and magnetic currents are derived using these coefficients at every point on the actual grating. Finally, integration of these equivalent currents over the actual grating gives the scattering of an arbitrary wave from a grating of arbitrary size and shape. The accuracy and validity of this method are also verified by experiments, where an arbitrarily-oriented grating is illuminated by either a plane or a spherical wave.