Phased array antennas are commonly used in earth stations because of their fast and accurate beam steering characteristics. The sidelobe of earth station antennas is strictly regulated internationally to avoid affecting the adjacent satellites. To suppress the side lobe of the phased array antenna, the accurate amplitude and phase of the signal must be fed to each radiating element. This paper proposed a method for calculating the amplitude and phase of a signal. The proposed method can rapidly and accurately calculate the amplitude and phase of each radiating element signal by setting an arbitrary phase in the radiation pattern reference. In addition, the proposed method was verified through a beamforming problem that satisfies the domestic radiation pattern reference.