ARTIFICIALLY SOFT AND HARD SURFACES IN ELECTROMAGNETICS

Soft and hard surface boundaries are well known from acoustics. In a recent paper, corresponding surfaces have been defined for dually polarized electromagnetic waves. These surfaces must be made artificially, e.g., by loading a conducting surface with corrugations. A transversely corrugated surface as used in corrugated horn antennas represents for instance a soft boundary. A hard boundary is available by using longitudinal corrugations filled with dielectric material. In the present paper the concept of such soft and hard surfaces is treated in more detail, considering different geometries. It is shown that both the hard and soft boundaries have the advantage of a polarization-independent reflection coefficient for geometrical optics (GO) ray fields so that a circularly polarized wave is circularly polarized in the same sense after reflection. The hard boundary can be used to obtain strong radiation fields along a surface for any polarization, whereas the soft boundary makes the fields radiated along the surface zero. © 1990 IEEE