In response to the development requirements of large-aperture，lightweight，and high-precision spaceborne deployable antennas，a support mechanism for large parabolic cylindrical spaceborne deployable antennas with a deployed aperture of 11 m×52 m is proposed and designed.Based on the characteristics of the mechanism composition，a spatial geometric model and a finite element model are established.A modal analysis is conducted on the mechanism by means of the Lanczos modal analysis theory，and the effects of the member size and material on the natural frequency are systematically evaluated.Additionally，the performance of the deployable antenna support mechanism is quantitatively evaluated by analyzing and calculating the mass-to-area ratio and f-number.The results indicate that the member size and support material are key factors affecting the dynamic characteristics of the antenna support mechanism.While ensuring the structural stiffness，the mechanism achieves lightweight design and possesses high pointing accuracy.