This paper presents a numerical and experimental study of RCS of canonical and complex targets using Gaussian Beam Summation (GBS) method. The purposed GBS method has several advantages over ray method, mainly on caustic problem. To test and evaluate the performance of the chosen method, we start the analysis of the RCS using GBS, the asymptotic models Physical Optic (PO), Geometrical Theory of Diffraction (GTD) and the rigorous Method of Moment (MoM). Then, we show the experimental validation of the numerical results using well calibrate measurements of radar targets. These experimental measurements have been carried out in our anechoic chamber (at ENSTA Bretagne). The numerical and experimental results of the RCS are studied and given as a function of various parameters: polarization type, target size, Gaussian beams number and Gaussian beams width.