We present an experimental validation of the numerical simulations of RCS using Gaussian Beam Summation method (GBS) in X band. In the high-frequency approximation, the main advantages of the GBS over ray method are related to the caustic problem. In this paper, the performance of GBS is illustrated with numerical and experimental evaluations of RCS of radar targets (flat plate, shell cylinder and a hollow cylinder with an aperture). The GBS method has been compared with Gaussian Beam Launching (GBL), classical Physical Optic (PO), and Method of Moment (MoM) and with experimental measurements. The experimental measurements have been realized in the anechoic chamber of the Lab-STICC (ENSTA Bretagne).