Abstract: This paper presents that periodic structure can be utilized to modify radiation characteristics of the original antenna array, in which the newly designed high-impedance periodic structure has improved the antenna gain under larger wide-angle scanning. The forward radiation of the antenna cell is improved by adding periodic structure, especially in an antenna array where the cell radiation pattern with periodic structure is much wider than that without it, thus allowing a relatively small decrease in the gain of array antenna when scanned at a wider angle. For instance, the gain of the antenna array with periodic structure is at least 4 dB higher than that without it when the beam is scanning at ±60°. Therefore, the newly designed periodic structure has ensured a relatively high gain of the antenna array under wide-angle scanning.