Abstract: A novel single-layer microstrip reflectarray element composed of a circular patch and a circular ring is presented. In order to evaluate the performance of the element, four parameters are summarized systematically，namely, the range of the reflection phase, the curve linearity, the sensitivity to fabrication tolerance and the phase bandwidth. Based on this, the performance function is defined. Spectral domain method of moment based on Rao-Wilton-Glisson(RWG) basis functions, which permits the analysis of arbitrarily shaped elements, is utilized to analyze the reflection properties of the proposed element. For the optimal parameters, the proposed structure offers the phase range in excess of 360° and a smooth reflection phase curve can be obtained with high linearity.