Artificially soft and hard surfaces in electromagnetics and their application

Transversely corrugated surfaces are widely used in the design of hybrid-mode horn antennas. The authors propose referring to such surfaces and their relatives by the common name ´soft´ surfaces. The reasons for this are that (1) these surfaces have the same characteristics relative to electromagnetic waves as the so-called acoustically soft surfaces have relative to acoustic waves, i.e., that the density-of-power flux along the surface is zero at the surface, and that (2) there also exists so-called artificially hard surfaces in electromagnetics, along which the power flux has a maximum for any polarization of the electric field. The authors define hard and soft surfaces in terms of an anisotropic surface impedance. Characteristics and possible applications of soft and hard surface are described.<>