Perturbation method in the problem of diffraction of an obliquely incident electromagnetic plane wave by an impedance wedge and the diffraction coefficients

We study the problem of diffraction of an EM plane wave by an impedance wedge. In the general case of oblique incidence the problem was not solved explicitly, however, in some special cases of surface impedances the analytic solution has been obtained. The most natural way to obtain the practically important results for the diffraction coefficient in the general case of skew incidence is to apply the perturbation method. The problem can be solved for the normal incidence and for the grazing to the edge incidence. This enables us to develop the perturbation procedure for the following two cases: for very skew and almost normal incidences