In this paper, a numerical and experimental investigation of electromagnetic scattering by a notched metallic disc is presented. Gaussian Beam Summation (GBS), Gaussian Beam Launching (GBL), Physical Optic (PO), Physical Theory of Diffraction (PTD) and Method of Moment (MoM) are applied for the simulation of the electromagnetic scattered fields. In addition, experimental measurements of Radar Cross Section (RCS) are realized in the anechoic chamber. A comparison between the different used methods is presented to demonstrate the validity of the proposed Gaussian approach (GBS and GBL). A study of the variation of RCS of a disc with and without a notch is conducted to determine the effect of the modification of the canonical structure on the scattered field.