Caustics problem is inherent to classical high frequency approximation such Geometrical Optics (GO), Geometric Theory of Diffraction (GTD), Uniform Theory of Diffraction (UTD) and Equivalents Current Methods (MCE). All these developments propose numerical estimations of the EM field scattered from reflection, diffraction, and multiple scattering from an object. In this paper we apply the Gaussian beam summation technique (GBS) to simulate RCS of radar target, especially for 5 to 10 wavelengths sizes. Gaussian beams are asymptotic solutions of the Helmholtz equation within the paraxial approximation. 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 formulation, the complete wave field at a receiver is evaluated as superposition of Gaussian beams concentrated close to rays emerging from the target, passing in a small neighborhood of 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). Simulation with canonical target shown will be compared to asymptotic methods (Physical Optic) and rigorous method (Method of moment)