An Improved GO-PO/PTD Hybrid Method for EM Scattering From Electrically Large Complex Targets

The accuracy and the efficiency of hybrid methods that combine geometrical optics (GO) and physical optics (PO), and physical theory of diffraction (PTD), have been improved by the use of backward-ray-tracing technique and Gordon’s integral algorithm. However, the overall accuracy of the method is still limited by the errors in the process of backward ray tracing. In this study, both the advantages and the disadvantages of the two techniques, namely, backward ray tracing and forward ray tracing, are compared. Also, the reasons for the errors in the backward ray tracing are explored in detail. On this basis, an improved ray-tracing technique is presented, called the two-scale division method (TSDM). This technique combines the advantages of forward and backward tracing, and it improves the accuracy of the GO-PO/PTD hybrid method. Meanwhile, the efficiency of the ray tracing is improved by using two-scale facets to structure the targets’ geometric model. The implementation principle of this method will be comprehensively discussed and it is validated by comparing the simulation results from FEKO-Multilevel fast multipole method (MLFMM), FEKO-ray launching GO (FEKO-RL-GO), and those from an unoptimized method.