Abstract: In this paper, a W-band elliptic cylindrical reflector with electronically large size is developed. Due to the geometric characteristics of double focus of the ellipse, the antenna has a narrow focal spot width in the near field, while in the far field can also has a high directivity by reasonably designing the aperture surface utilization and antenna efficiency. It is suitable for the target detection radar that requires high cross range resolution in both midrange and long range. In order to reduce the workload of simulation optimization, a simplified design method is proposed to improve the efficiency of design. Finally, the far-field radiation pattern of antenna has been tested by a Compact Range (CR) measurement system, and the focal spot width of antenna has been measured by the object detection experiment. The measured data are in good agreement with the simulation results, thus proving the reliability and accuracy of the design process.