| Research Abstract |
The electromagnetic scattering problems from three dimensional objects with arbitrary shape were investigated by the equivalent dipole method, which approximates the scattering fields in terms of the fields generated by the hypothetical multiple dipoles. The perfectly conducting and the dielectric cylinders of finite length with rotational symmerty were first examined as an example scatterer, and their edge effects on the radar cross sections and the scattering fields were investigated in comparison with the results obtained by other method and also with experiments in the X band. As a result, it was found that for the perfectly conducting cylinder, the forward and backward radar cross sections could be accurately calculated by the present method whether the scatterer may or may not have edges, whereas the numerical precision of the scattering field patterns were much affected by the existence of an edge. On the other hand, those for the dielectric cylinder were accurately calculated e
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ven if the scatterer has an edge.
Next, we proposed the two efficient approaches incorporated with the equivalent dipole method, which were useful for a scatterer with large diameter and for a slender one respectively. The former is the multiphase-illumination approach based on the symmetric coordinates and the latter is the partially two-dimensional approach which regards the central region of a slender scatterer as the two-dimensional structure. Especially, the latter approach was successfully applied to the analysis of the thin wire antennas with finite length and finite diameter. Then it was clear that the characteristics of the half-wavelength antenna are affected when the diamiter or the feeding gap interval becomes larger than the order of a hundredth of the wavelength.
Finally, as an example of the 3D object with arbitrary shape, the perfectly conducting cube including many singular edges and corners was investigated. The numerical results of the radar cross section showed good agreement with the experimental ones and so it was confirmed that the equivalent dipole method was very useful for analyzing the 3D scattering problems. Less
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