Comments on "Electromagnetic wave scattering by an infinite plane metallic grating in case of oblique incidence and arbitrary polarization

In a previous paper by K. Uchida et al. (see ibid., vol.36, no.3, p.415-22, 1988) it is claimed that in the case of an arbitrary polarized plane wave incident on a strip grating, it is necessary to investigate the quasi-two-dimensional problem where the separation into transverse magnetic (TM) and transverse electric (TE) waves is, in general, impossible. It is shown here that although in general, arbitrarily polarized incident wave case decomposition into TE and TM waves is impossible, it is possible to divide any electromagnetic field into two orthogonal components; (1) fast polarization where an H-field component parallel to the strips is zero and (2) slow polarization where an E-field component parallel to the strips is zero.<>