Gaussian beams are asymptotic solutions of the Helmholtz equation within the paraxial approximation. As the amplitude distribution of these solutions along the direction perpendicular to the ray is Gaussian, with its maximum on the ray, these solutions are called Gaussian beams. Since they are insensitive to ray transition region, several techniques based on Gaussian beam are used to evaluate high frequency EM wave equation, which overcome partially or fully the difficulties of singular regions (caustics, zero field in shadow zones). In this paper we simulate RCS of a radar target using Gaussian beam summation method (GBS). The complete wave field at a receiver is evaluated as superposition of Gaussian beams concentrated close to rays emerging from the target, passing through the receiver. When the incident field strikes the edges, the diffraction is accounted in a complex weighing function, applying the geometrical theory of diffraction (GTD) [3].