Diffraction at artificially soft and hard edges by using incremental theory of diffraction

Control of the radiating characteristics of high performance antenna systems is discussed. To this end, undesired scattering mechanisms may be reduced by conveniently shaping or corrugating the scattering surfaces. A systematic method for characterizing corrugated surfaces for different applications has been presented in Kildal (1991). There, it was suggested that suitable combinations of corrugations and dieiectric loadings may usefully be employed to devise surfaces that exhibit artificially soft and hard boundary conditions. It has been shown that this technology may provide effective tools to control the side-lobe level and cross-polar components of radiation patterns. Within this framework, an accurate description of diffraction mechanisms at edge discontinuities is relevant for an exhaustive examination of the polarization effects. Uniform, incremental diffraction coefficients at edges in artificially soft and hard surfaces have been obtained in Maci et al., that provide basic tools for treating the scattering at actual edge configurations of practical interest. These are obtained according to the incremental theory of diffraction (ITD) (Tiberio et al., 1990, and Tiberio and Maci). These coefficients yield a representation of the field which is uniformly valid at any observation aspect, including caustics of the corresponding ray-field description. In the present paper, the effectiveness of the ITD coeffcients is demonstrated in the example of vertical monopole on artificially soft disc. The accuracy of the results is tested by comparison.