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

In article the problem of scattering of electromagnetic waves on complex shape objects in sub-millimeter and terahertz waves is considered. To calculate the signals reflected from the target the polygonal model is used. The polygonal model represents an external surface of the target in the form of an array of the plane triangular elements joined with each other. The signal reflected from the target represents as superposition of elementary signals from triangular elements of polygonal model. The article purpose is adaptation of polygonal model to sub-millimeter and terahertz waves for definition of maximum restrictions on the size of a triangular element of polygonal model in relation to length of a wave. It is necessary to establish the maximum size of a triangular element of a polygonal model on the basis of electrodynamic criteria. In article scientifically well-founded requirements to a choice of the size of a triangular element of polygonal model for providing of a required level of an error of calculations of the reflected signal from the target in comparison with exact diffraction decisions and experimental data are formed. The radar cross section (RCS) of the targets in sub-millimeter and terahertz waves is defined as a result of superposition of complex coefficients of reflection of elements of polygonal model which are calculated on the basis of methods of physical optics (PO), the physical theory of diffraction (PTD) and shooting and bouncing rays (SBR). For practical use of these methods to elements of polygonal model algorithms of calculation of shadings of triangles and traces of beam tubes for rereflections of waves are developed. For reception of authentic results of calculations of input signals of radar systems it is necessary to establish number of triangles of polygonal model of target (rocket or plane) about some tens or hundreds thousand. Thus calculation of the reflected signals occupies significant time. The most significant time is spent for realisation of algorithms shading triangles triangles and calculation of beam tubes for rereflections. Therefore it is required to define the optimum size of a triangle when requirements on accuracy of calculations are satisfied for the limited number of triangles of polygonal model of the target. The algorithm of a choice of size of a triangular element of polygonal model for calculation of the reflected signals in sub-millimeter and terahertz waves is formed on the basis of calibration of mathematical model with use of etalon reflectors (sphere), the exact decision for which it is known. As a result of use offered technique it is shown that as parameter of polygonal model which directly influences on accuracy of calculations is the maximum size of the triangle at the relation of the size of object and length of wave. As the most rational approach to the decision of a problem of definition of demanded accuracy of calculations at the relation of time for calculations it is recommended to carry out calibration of mathematical model on the developed algorithm in each specific case (a parity of the linear size of object, the size of a triangle and length of wave). As a result of calculations diagrams of RCS of fighter F-117 on frequencies f=330 GHz and f=1.6 THz are calculated for a case when the plane surface is ideally smooth.