The Fast Physical Optics Method With the Linear Amplitude and Quadratic Phase Terms

The physical optics (PO) scattered fields from the electrically large scatterers contain slowly varying amplitude and highly oscillatory phase terms. In this work, first, we consider quadratic approximations for the phase term of the PO scattered fields. Second, the linear amplitude of the PO scattered fields [linear-fast PO (L-FPO)] is proposed. The simplification of the linear amplitude term is adopted for two reasons. One is that the contributions of the PO scattered fields mainly come from the high-frequency critical points, that is, the stationary phase points, the boundary phase points, and the vertex points. When the wave frequency goes large, the linearization of the amplitude term could guarantee the accuracy of the PO scattered fields from the high-frequency critical points. The other reason is that the L-FPO method proposed in this work avoids the time-consuming and complicated calculation of Fresnel integrals. The computational cost of the Fresnel integrals is shrunk drastically. For the aircraft model, the CPU time of the proposed method is reduced by one order of magnitude compared with Gordon’s method and nearly half compared with the Q-FPO method. In the process of the PO method of determining the lit region of the scatterer, the new shadowing technique pairing a quadratic quadrilateral patch into two subtriangles achieves high accuracy in the determination of the shadow boundary.