Large spacing is widely used in building large scale ground based solid state phased array due to the cost. Grating lobe will appear under this large spacing, which leads to performance deterioration. The sweep angle can be broadened by using the thinning method. In this paper, the array design methods are studied, and an unequal spacing optimization method is presented. An array with grating lobe lower than -20 dB is implemented in ±20° sweep angle by using λ×λ element. The number of units is reduced by 18% due to the enlarged aperture.