It is well-known that calculation of scattered fields at high frequencies is consuming too much CPU time and memory allocation. The exponential model is used to predict the high frequency values in the radar cross section (RCS) calculation. The Prony’s and Matrix-Pencil methods are presented to extract the parameters of exponential model. In particular, the Matrix-Pencil method is modified to increase the efficiency. Both methods are applied to a reference scatterer (a perfect electrically conducting sphere). Also, a new modelling scheme is proposed using the Legendre-basis functions. This approach is tested in the calculation of the bistatic RCS values.