METHOD OF EQUIVALENT CURRENTS FOR CALCULATION OF SURFACE DIFFRACTION BY A SMOOTH CONVEX OBJECTS

A high-frequency approximate method for calculating the diffraction by a smooth convex surface is presented. The advantage of this method is the validity of it in the caustic region of the creeping rays where t he Geometrical Theory of Diffraction (GTD) becomes invalid. The concep t used in this method is based on the Method of Equivalent Edge Curren ts (EEC), and the equivalent line currents for creeping rays which are derived from the diffraction coefficients of the GTD are used. By eva luating 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 metho d, the diffraction problem by a perfectly conducting sphere of radius a is solved by applying the method, and the obtained results are compa red with the exact and the GTD solutions. It is confirmed from the com parison that the failure of the GTD near the caustic is removed in thi s method and accurate solution is obtained in this area for high-frequ ency (ka greater than or equal to 8). Furthermore, it is also found th at this method is valid in the backward region (0 degrees less than or equal to theta < 90 degrees, theta is an observation angle mesuered f rom an incident direction), whereas not in the forward region (90 degr ees < theta less than or equal to 180 degrees).