In this study, single layer microstrip reflectarray antenna design and analysis for X-band (8-12 GHz) applications are performed. A new unit cell has been designed to achieve phase change in linear form. This structure composed of interdigitated diamond-shaped geometry and it is printed on a thin dielectric substrate with epsilon(r)=3 dielectric permittivity and h=1.524 mm thickness. 420(0) phase range is obtained by this new design unit cell. The size of 9x9 reflectarray antenna is 153mm x 153mm. The pyramidal horn antenna is used for center-feed configuration. The required phase delay compensated by using variable size unit cell element and the main beam directed to the desired direction (theta=0(0)). The designed reflectarray antenna is practically realized and the measurements are done in non-reflective room. The performance of reflectarray antenna is verified by measurement and simulation results. Obtained simulation and measurement results are in harmony with each other. The maximum gain value is 22.25 dB at 10.7 GHz, 1-dB gain bandwidth is 20% between 9.75GHz-12 GHz and 3-dB gain bandwidth is 27% between 9.1 GHz-12 GHz.