Method of Equivalent Currents for Calculation of Surface Diffraction by a Smooth Convex Objects (Special Issue on Electromagnetic Theory : Foundations and Applications)

概要

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A high-frequency approximate method for calculating the diffraction by a smooth convex surface is present-ed. The advantage of this method is the validity of it in the caustic region of the creeping rays where the Geometrical Theory of Diffraction (GTD) becomes invalid. The concept used in this method is based on the Method of Equivalent Edge Currents (EEC), and the equivalent line currents for creeping rays which are derived from the diffraction coefficients of the GTD are used.By evaluating the radiation integral of these equivalent line currents, the creeping ray contribution which is valid within the caustic region is obtained. In order to check the accuracy and the validity of the method, the diffraction problem by a perfectly conducting sphere of radius a is solved by applying the method,and the obtained results are compared with the exact and the GTD solutions. It is confirmed from the comparison that the failure of the GTD near the caustic is removed in this method and accurate solution is obtained in this area for high-frequency (ka ≥8). Furthermore, it is also found that this method is valid in the backward region (0゜≤θ< 90゜,θis an observation angle mesuered from an incident direction),whereas not in the for-ward region (90゜<θ≤180゜).
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1996-10-25