Abstract: In this paper, an improved iterative fast Fourier transform (IFFT) based on the mutual coupling compensation matrix (MCCM) is introduced and applied to the low-sidelobe synthesis of wide-angle scanning phased arrays. Firstly, the MCCM is integrated into the IFFT to take into account the mutual coupling effects between the array elements. In this situation, the far field of an array which takes the mutual coupling into calculation can satisfy the principle of pattern multiplication. Secondly, a wide-beam element antenna backed by a substrate integrated waveguide (SIW) cavity is proposed. The proposed wide-beam antenna can simultaneously excite the TE₁₁₀ and TE₂₁₀ modes to expand its operation bandwidth. Based on this element, three wide-angle scanning phased array antennas with 35, 75 and 100 elements are formed and calculated. Finally, the proposed IFFT algorithm is used in the low-sidelobe synthesis of the three phased arrays. Compared with the results of the genetic algorithm based on the active element patterns, this algorithm can realize low-sidelobe performance within the scanning range from −60° to 60° at faster speed.