Abstract: The developments of anti-stealth technology pose a strong challenge to the stealth performance of military aircraft. The classical electromagnetic adjoint approach cannot obtain the surface sensitivity information, and therefore cannot provide intuitive guidance for optimal design. And in classical adjoint approach, the needs to fill impedance matrix repeatedly during gradient calculation lead to low efficiency when the number of design variables and incident angles are large. This paper proposes an approach to calculate radar cross section surface sensitivity based on adjoint and automatic differentiation method. And a sparse matrix storage method considering the characters of RWG basis function is adopted to reduce the memory requirements of impedance matrix differentiation. The proposed method can obtain the surface sensitivity of all surface nodes with one matrix differentiation calculation. For different incident angle, the calculation of design variable gradients of any number will not exceed 16 matrix-vector products. The proposed surface sensitivity calculation approach can effectively improve the efficiency of gradient calculation and provides support to the optimal design of stealth military aircrafts.

Key words: electromagnetic adjoint equation, surface sensitivity, radar cross section, automatic differentiation