This article deals with the study of backscattering of large target in a close environment. Due to the large size of the target, it cannot be considered as illuminated by a single wave hence the classical far-field assumptions is not verified. Based on high-frequency approximations like Physical Optics (PO) and Incremental Length of Diffraction Coefficient (ILDC), a model is established to evaluate the response of a close target in term of Radar Cross Section (RCS). The model is established with an optimized subdivision technique to manage the near-field contributions and validated trough full-wave simulation.