A single-layer wideband reflectarray antenna using clip-shaped elements for X-band applications is proposed. A linear phase shift of 398° can be achieved by adjusting the longitudinal length of the interior folded slot of each element, while the exterior dimensions of each element remain identical. In this layout, a prolonged current path for an increased phase swing can be obtained and the sudden size variation between adjacent elements in the array can be avoided. A reflectarray antenna that is offset-fed and composed of 529 elements is modeled, manufactured, and tested, with a 0.3λ unit cell periodicity at the design frequency of 10 GHz. Experimental results exhibit that for 1-dB gain drop, a broad 41.0% bandwidth is obtained. The tested gain is 25.7 dBi at 10 GHz, which corresponds to aperture efficiency 68.5%. Additionally, stable and good radiation characteristics are also achieved.