Abstract: Spaceborne deployable active phased array antennas achieve a larger physical aperture through space deployable structures. Reflector antennas have a good stowage ratio and are commonly used forms of antennas in spaceborne radar systems. To realize a high stowage ratio and lightweight deployable antenna, a combination of windable rib deployable antenna structures with ring-focus Cassegrain antenna technology is proposed. This results in an X-band ring-focus Cassegrain reflector parabolic windable rib deployable antenna structure, which offers advantages of light weight and high stowage ratio. This paper provides the design process of this windable rib antenna structure, verifies through simulation and analysis that this design satisfies project requirements, and validates through scaled model testing that the performance metrics during deployment meet the requirements. This reduces the stowed size of the reflector-based spaceborne SAR antennas and lowers launch costs.