Aerodynamics and radar signature - A combination of theoretical methods

Abstract

Combat aircraft are threatened by radar-controlled anti-aircraft systems. Knowledge of the scattering of electromagnetic waves from aircraft allows aerodynamic designers to design a low radar signature or to improve the tactics of aircraft in service to successfully avoid enemy defensive reaction. A theoretical approach is presented to estimate the radar signatures of complex aircraft configurations including external stores. The signature is evaluated by determining the radar cross sections of intended radar-observation directions. The radar cross section of a certain aspect view of a radar observation is evaluated by combining specular geometrical and physical optics for curved-surface elements, such as wing surfaces, that are large with respect to the radar's wavelength. Diffraction formulas are added to introduce the radar-reflection characteristics of edges. The geometric input is equal to the buildup of usual aerodynamic panel methods and, by the evaluation of the panels' principal curvatures by higher-order means, allows the regard of the curved aircraft surfaces. The diffractions typical for edges (wing edges, etc.) are included with regard to the edges' sharpness and geometric shape. The total radar cross section is determined by summing up all reflecting areas (by the combination of the contributing panels) and edge elements. Thus, an aerodynamic surface discretization can be used without modification. The signatures of principal bodies and a fighter aircraft, both armed and unarmed, when exposed to a typical radar illumination, are presented.