Surface Wave Excitation at Edges in Anisotropic Impedance Surfaces

Abstract

In the latest years, an increasing interest has been devoted to the design and fabrication of composite materials [1] exhibiting specific electromagnetic properties. Artificial surfaces, as for instance, dichroic screens, polarization selective surfaces, absorbers, or more complex multi-layer and periodic structures, are being often and often applied in antenna and microwave device technology. The electromagnetic analysis of the above surfaces is usually focused on their reflection and transmission properties, which can be determined by referring to the corresponding infinite planar composite surface under plane wave or, more rarely, dipole excitation. However, in many applications it is important to include edge effects. In this framework, accurate numerical methods have been developed to study surface wave phenomena in finite periodic surfaces [2], and efficient diffraction coefficients have been proposed to evaluate the scattering from edges in composite material surfaces when they can be characterized by proper anisotropic impedance boundary conditions (IBC’s). Indeed, the introduction of suitable IBC’s allows us to extend analytical high frequency techniques (as for instance the Uniform Geometrical Theory of Diffraction and the Physical Theory of Diffraction) to the analysis of edge effects in non-metallic composite surfaces. This approach represents a very promising alternative to pure numerical methods, when dealing with electrically large reflectors or screens. The first step toward the derivation of closed form expressions for the edge diffracted field is the development of an analytical model of the surface, i.e.,an approximate IBC which must be satisfied by the total field right at the exterior surface of the structure.