In this study, the investigation of the electromagnetic scattering by modified targets is presented. A metallic notched plate and disc are considered. Two Gaussian beam (GB) techniques have been applied: GB launching (GBL) and GB summation (GBS). The theoretical formulations of GBL and GBS are established. The simulations of the radar cross-section (RCS) of the flat and notched targets (plate and disc) are presented. The application and evaluation of GBS and GBL methods are extended through the studied variations of the RCS in several scattering angles and different radar frequencies. The numerical RCS results are compared with those given by the physical optic model and the method of moments. Moreover, the numerical results are evaluated with measurements conducted in an anechoic chamber.