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Stealth performance is one of the most important features required for modern military aircraft design with the development of military technology. The most reflective part of radar waves in an aircraft structure is the front fan of the engine located inside the intake. Therefore, the method of designing the inner duct in a S-shape as in the case of F-22 or installing a steel mesh width smaller than the radar wavelength in the intake as in the case of F-117 is used for low observation of radar detection. However, in such cases, there is a disadvantage of lowering the engine intake efficiency.

Considering the difficulty, this study proposes an electromagnetic wave reflecting structure to be attached in front of the intake, near the entrance of intake. The advantage of this approach is that there are relatively less structural changes in the aircraft than other methods. In general, the development of radar scattering structures depends on the intuition of the engineer. However, such approaches are less systematic. To overcome such drawbacks, our study used the reaction-diffusion equation-based topology optimization method for design of radar reflection structures. [1] Considering that the operating frequency of the tracking radar is generally at X-band frequency range, the target frequency of the EM wave is set to 10 GHz. Because the study aims to reduce the radar cross section caused by the aircraft engine intake, design objective is to minimize returning waves to the radar source. In addition, considering the varying radar wave incident angle, the design sensitivity is set to the weighted sum of each case. The angle of incidence was set to vary from 0˚ to 20˚, considering the general operating altitude and distance from the radar. The structure consists of Al₂O₃ and the electromagnetic reflection performance is measured by the S₁₁ parameter. We set design domain considering air flow and structure-fluid analysis was also performed. For finite element analysis and design process commercial packages COMSOL and MATLAB were used.

computation;topology optimization; s-parameter; x-band