Abstract: Considering the drawback of weak twisting stiffness of the feed cable-suspended structure for the next generation large spherical radio telescope, a method is proposed to enhance the twisting stiffness of the structure through adding the stable cable system. The stable cable system consists of three tie-down cables. The upper end and the lower end of each stable cable are connected respectively with the feed cabin and a clog through a guiding pulley. While the cable-suspended structure vibrates under some external disturbance, the stable cable system acts as a dynamic absorber to enhance the stiffness of the structure effectively. Considering the effect of weight on the shapes and the tensions of the long span cables, the nonlinear equivalent equations of the feed cable-suspended structure including the stable cable system are established. A comparison of the structural displacement responses induced by the external disturbances between the original structure and the improved structure is made. Then, the effectiveness of the proposed method is demonstrated through the experiments of 5 m scaled model. Furthermore, the antenna pattern is drawn，and the quantitative analysis is made to evaluate the effect of the stable cable system on the electromagnetic performance of the antenna in view of the gain, cross polarization, and first minor level. Both the theoretical analysis and the experiments show that the feed cable-suspended structure with stable cable system can be applied to the 500 m antenna project.

Key words: Cable-suspended structure, Electromagnetic performance, Feed cabin, Model experiment, Stable cable, Stiffness, Super antenna