An experimental study was made to produce a thin screen that absorbs electromagnetic waves at the edges as well as over its surface. Previous screens, built as quarter-wave interference absorbers for microwaves, have been highly absorbing for waves normally incident on flat surfaces but have reradiated at the edges as strongly as a metal screen. The dielectrics in the sandwich of an interference absorber are lossless. The carbon-impregnated dielectrics which were used to coat the metal disks in this study, unlike the interference absorbers, reduced the edge radiation. Since the measurement of near-field patterns of disk antennas is much simpler than the measurement of near-field diffraction patterns of a disk, these introductory studies were made on disk antennas. The evanescent standing wave over the surface of the disk antenna and the radiated wave were proved to be independent, in that the intensity of the surface wave could be reduced an order of magnitude more than the radiated wave by the absorbing coat. An absorbing coat on the disk antenna reduced the intensity without changing the shape of the radiated field pattern.
© 1968 Optical Society of AmericaFull Article | PDF Article
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