Radar cross section minimization for step structures using topology optimization

The electromagnetic performance of flight vehicles has been attracting considerable interest in recent years. As one of the important indicators of this performance, radar cross section (RCS) has been extensively studied. A significant limitation on the RCS of flight vehicles lies in the fact that tiny gaps will transform into steps during structural deformation, where the local RCS will be significantly affected. This study investigates a topology optimization method to minimize the RCS of step structures when subjected to external loads. To ensure that the structure discretized by shell elements in the mechanical finite element analysis can still simulate the wave reflection of step structures, artificial step elements are defined to simulate the generation of steps during structural deformation. Then, the conventional method of moments is utilized to calculate the RCS. To implement the gradient-based optimization, the sensitivity of RCS with respect to the design variables is derived analytically by the adjoint method. An extended compliance-based topology optimization is performed to determine a stiffness constraint. Then, together with a structural volume limitation, the average RCS of target incident angles will be set as the object to obtain the structural topology. The superiority compared with the general structural design method and the validity have been demonstrated with numerical examples.