One of the common ways to design large arrays is by designing a small subarray known as cluster and using it as a repeating element throughout a large array. In this paper, the genetic algorithm is used to optimize the clustered amplitude tapers such that the final array pattern has minimum grating lobes and controlled sidelobe level. The formulation of the synthesis problem includes the minimization of the excess magnitude of the grating lobes or peak sidelobes which are usually higher than a given allowable limit. Moreover, two clustered configurations based on increased/decreased number of elements per cluster around the array center are introduced. Correspondingly, their clustered sizes increase/decrease as they approach the center of the array. Simulation results show that the proposed method has capability to optimize clustered linear and planar arrays without noticeable appearance of undesirable grating lobes. The analysis for an array composed of 20 elements with clusters of different cluster sizes M = 10, 8, 5, 4 and different numbers of elements per cluster Ns = 2, 3, 4, 5 elements found that the complexity reductions were 50%, 60%, 75%, 80%; peak sidelobe levels were -29 dB, -23.6 dB, -21.3 dB, -19.15 dB; and the directivities were 25.53 dB, 25.64 dB, 26.33 dB, 26.32 dB, respectively.