Gratings composed of helically conducting cylinders

The problem is the diffraction by a grating composed of helically conducting cylinders of radius b with twirl angle Ψ, irradiated by an arbitrarily polarized normally incident plane electromagnetic wave. The helical curves are taken to be right-handed. The grating spacing p is assumed to be less than the wavelength λ. That ensures the absence of lateral spectra. Two classes of gratings are considered: with perfect electric and magnetic conductivity of the cylinders simultaneously, and with the electric conductivity only