Application of a rigorous modal theory to electromagnetic diffraction from a biperiodic rough surface

A rigorous modal theory is described for the study of the diffraction of electromagnetic plane waves by bigratings of hemispherical cavities hollowed in a plane surface of perfectly conducting material. The theoretical study is realized for any incidence and direction of polarization and our first numerical results concern only the simpler case of normal incidence. Under this condition the efficiency curves of the various real diffracted orders are studied. We find that the cavity depth has an important influence on the shape of the curves. In particular, the