Abstract: Aim The optimization and synthesis technique and mutual coupling compensation technique for ultralow sidelobe phased arrays were discussed. Methods A direct optimization method for the correction of the element mutual coupling was presented. This method takes the element mutual coupling directly into the optimization computation and applies the nonlinearly constrained optimization algorithm to the synthesis of the ultralow sidelobe phased arrays. With this method, arrays synthesis and mutual coupling compensation were accomplished at the same time. Results Some computing results obtained with this method were given. Conclusion For this method, only stimulation amplitude was adjusted to realize ultralow sidelobe and mutual coupling compensation of phased arrays. It is of benefit to engineering.