In order to use parabolic antenna to generate scanning beams, excitations of the feeding array are adjusted. Single-feed parabolic antenna patterns are calculated using PO, and based on this, the excitation coefficients of the array are optimized by solving the least-squares problem and the antenna pattern is synthesized efficiently to control the side-lobe level and cross-polarized components, and to scan the beam direction. Numerical simulation results are given to verify the feasibility of this method.