The Concept of the Scattered Field and the Finite-Difference Time-Domain Method of the Scattered-Field Formulation

摘要

This communication presents a discussion on the concept of the scattered field for both the steady-state and the transient analyses. It is shown that the scattered field defined by this concept is fictitious as it does not, in general, correspond to the physics of the scattering phenomenon. When applied to the finite-difference time-domain (FDTD) method, the concept of the scattered field results in the FDTD method of the scattered-field formulation. It is shown that such an FDTD can produce significant errors in the distribution of the scattered near-field behind a perfect shield of infinite transverse dimensions. Nevertheless, our numerical technique for computing the values of the plane-wave scattering coefficients is still shown to be very accurate in spite of these errors, because scattering parameters are far-field parameters and because these scattered near-field errors consist of evanescent fields that do not subsist in the far-field. Therefore, the FDTD method of the scattered-field formulation and, by the same token, the concept of the scattered field can be used reliably for computing far-field parameters (e.g., plane-wave scattering coefficients, radiation patterns, and radar cross section), but they should be used with caution for computing near-field parameters (e.g., near-field distribution, input impedance, and specific absorption rate).