Abstract: For tedious design of power divider in traditional array antenna design process, based on the -3 dB beam width in height is from 0° to 12°, -10 dB beam width in height is from 12° to 65°, total height coverage is 65°, the center frequency is 9.05 GHz cosecant squared expanded beam informs requirements, this paper designs a new serially fed structure Gysel power divider with fixed amplitude and phase-only control. This power divider amplitude as a fixed value and only using the phase to control antenna's beamforming. Using genetic algorithm, it can realize accurate beamforming of the cosecant squared expanded beam and use less time to complete the design.