In open periodic waveguiding structures Bragg scattering can be observed in different forms [1]. Type of the wave transformation depend on from a value of perturbation period. If a perturbation wavenumber is twice as large as longitudinal wavenumber of surface wave, then coupling of two surface waves with opposite propagation directions occurs, that is reflection of surface waves is observed [2]. If a wavenumber of the perturbation is equal to difference of longitudinal wavenumbers of surface and volume waves then a coupling of these waves secures, that is why we can obtain output of radiation from structure [3]. Open inhomogeneous structures become more interesting and useful when parameter perturbation is not periodic. If amplitudes of spatial harmonics of perturbation are not constant, input of incident radiation into open waveguide is possible [4]. It is theoretically and practically important to consider combination of these phenomena [5]. Such a combination is more easily achieved for not equidistant wavenumbers of perturbation space harmonics.

In the present paper physical effects of coupling of waves at plane with spatially oscillated surface impedance are theoretically investigated. A combination of two processes is investigated. The first process is reflection of surface waves propagating along impedance surface. The second process is an input-output coupling of incident paraxial wave electro-magnetic beam with both surface waves. This electromagnetics problem is important for consideration of devices combining functions of antenna and microwave generator.