A.B. Borzov, K.P. Lihoedenko, I.V. Muratov, G.L. Pavlov, V.B. Suchkov

Because of wide development of radar systems of sub-millimeter and terahertz ranges the problem of creation of mathematical model of their input signals from complex shape targets is actual. In sub-millimeter and terahertz ranges the surface roughnesses of the target have considerable influence on characteristics of scattering of the targets because sizes of roughnesses are comparable to length of a wave. In such conditions the field of scattering of the target differs from a field of scattering of a smooth surface as surfaces of all real objects are always rough. Use of polygonal model as a mean of the description of geometry of the target is proved because of accuracy of representation of geometrical shape of the target. Article purpose is specification of a technique of calculation of characteristics of scattering of the targets in the form of polygonal models, for a case when on a target surface chaotic roughnesses are located. The mathematical technique which allows to describe statistics of roughnesses of the surface located on a surface of the target is developed. At creation of the technique known mathematical methods, such as a method of a tangent plane and a method of small roughnesses have been used. Statistical parametres of roughnesses, electrodynamic parametres of polygons and mathematical models of calculation of fields of scattering are integrated in object-oriented method. In the article digital simulation of characteristics of scattering of the targets is carried out and dynamics of change of a signal in dependence of size of roughnesses is analysed. For an estimation of influence of a roughness on a target surface on level of the reflected signal calculations of radar cross section of ideally smooth sphere and sphere with roughnesses on frequencies f=330 GHz and f=1.6 THz are carried out. Appearing of fluctuations of radar cross section of sphere with roughnesses is described. As a result of calculations diagrams of radar cross section of fighter F-117 on frequency f=330 GHz are calculated for a case when the plane surface is covered by roughnesses with size of 5 mkm.