This paper presents a novel deployable antenna mechanism for synthetic aperture radar (SAR) satellites. First, the topological structure of the new deployable mechanism is designed based on the five conditions expected to be satisfied. Then, the kinematic model of the new mechanism is fully established based on vector equations and structural symmetry. Third, the deployed/folded ratio and interference of the new mechanism are analyzed. Finally, a typical numerical example is used to illustrate the effectiveness of the theoretical analysis, and a physical prototype is developed to show the fabrication feasibility of the new deployable mechanism. Compared with the latest counterpart for SAR satellites in the existing literature, the new deployable mechanism of this paper has a simpler driving system, simpler deployment movement, and no prismatic pairs with cold welding problems. With these characteristics, the presented new mechanism has a good application prospect in SAR satellites.