Résumé
The C-method is one of the most efficient and versatile methods designed for diffraction gratings. Its strength lies in the use of a coordinate system in which the surface of the grating coincides with a coordinate surface. The result is a great simplification in writing the boundary conditions. We exploit this simplification to treat the problem of diffraction from curved strip gratings, and we use the combined boundary conditions method that has been introduced for planar strip gratings and proved to be very efficient