Parameterization of the tapered incident wave for numerical simulation of electromagnetic scattering from rough surface

The tapered wave with the tapering parameter g has been applied to numerical simulation of electromagnetic scattering from randomly rough surface with illuminated finite surface length L. This communication presents how to select the parameters g and L, and shows quantitative relationship with the incident angle. The parameter g, as a function of incident angle, should be large enough to make the wave equation in the range of allowable error. The surface length L, larger than several correlation lengths, should be large enough to suppress the punctuated power at the surface edges and be limited to make efficient computation. Combining these criterions, a graphical format to locate g and L for different incident angle θ_i is illustrated. An empirical formula for selecting g and L as a function of θ_i is proposed.