<p>With the increasing demand for large-aperture reflectors in deep space exploration missions, achieving a synergistic optimization of antenna structural stiffness and lightweight design while ensuring electromagnetic performance has become a critical challenge in this field. This paper investigates the application of fiber-reinforced composite materials in antenna backframe structure and proposes a concurrent optimization method for antenna backframe structure based on fiber-reinforced composites. Firstly, an improved discrete–continuous parameterization optimization method (IDCP) is introduced, which constructs a discrete material interpolation model based on the Sigmoid function. The steepness of the function is dynamically controlled by a penalty factor, enabling rapid discretization of angle subinterval selection variables to either 0 or 1. This approach effectively balances the suppression of material phase ambiguity and the improvement of convergence efficiency, significantly enhancing the convergence rate of both macroscopic topology configurations and microscopic fiber arrangements. Secondly, a concurrent topology optimization model for the antenna backframe structure based on fiber-reinforced composites is established, considering the electromagnetic performance requirements of the antenna backframe's supporting surface. By introducing shape feature constraint functions into the design domain, the structural stiffness is weighted and restructured, reshaping the stiffness distribution within the design domain. Finally, by adjusting the influence factor in the shape feature constraint function, a truss structure with clearly defined members is obtained, ensuring that the optimized antenna backframe structure not only meets the electromagnetic performance requirements but also achieves the goals of lightweight design and high stiffness.</p>