In this letter, a low RCS patch antenna array based on integrated of radiation and scattering performance has been designed. The 4×4 array is comprised of two different antenna units, which have similar radiation characteristics but 180° reflection phase difference. By using genetic algorithms, aperiodic configuration can be obtained, which makes the scattering field evenly scattered in all directions and effectively reduces the peak value of RCS. Simulation results shows gain of the proposed array is more than 16 dBi. Under xpolarization the monostatic RCS in normal direction is reduced from 8 GHz to 15.9 GHz and the peak reduction is 17.1 dB. Under y polarization the monostatic RCS in normal direction is reduced from 9.5 GHz to 16 GHz and the peak reduction is 13.1 dB. The proposed array was manufactured for test and the measured results show good agreement with the simulation results. The proposed array has characteristics of metamaterial and patch antenna. The RCS is reduced because of phase difference of antenna units without any other metamaterial, which provides a new method to reduce the RCS of the antenna array.