Study On The Algorithm Of Wideband Scattering By Electrical Large Complex Target

High-resolution radar has a wide application prospect in the field of imaging, detection and recognition because it can provide high precision image full-time and full-weather. High resolution usually requires high operating frequency and bandwidth, which makes the operating frequency go into the infrared and even Terahertz frequency range. As the basis of radar target recognition, high resolution imaging highly depends on the analysis of electromagnetic scattering from the target. On one hand, the computation of the electromagnetic scattering from electrically large complex targets becomes difficult to solve due to the increasing of electrical size of the targets. On the other hand, the demand of quickly and accurately obtaining the target’s wideband even ultra-wideband electromagnetic scattering characteristics grows rapidly since the operating frequency bandwidth of radar raises.Therefore, research on the algorithm of wideband electromagnetic scattering by electrical large complex target has great theory significance and military application value. Based on all above, this paper focuses on the following:1. Graphical-electromagnetic computing (GRECO) method is applied to calculate the radar cross section (RCS) of the electrical large targets in Terahertz-band. Partition display algorithm is adopted to solve the problem of insufficient screen pixels to meet the requirements of accuracy, which will make the subregion of the target successively displayed on the screen, and extract the pixel information to be used in subsequent calculations. OpenMP technology and OpenGL display list are applied to speed up the calculation and deal with the huge number of mesh grids of the targets. Then the electromagnetic parameters variations with frequency of three kind of commonly used metal are calculated by introducing in the Lorentz-Drude model. Finally a metal plane model illuminated by perpendicular incident electromagnetic wave is set up as an example to discuss the variation of RCS of metal target with the frequency from microwave band to terahertz and optical band.2. Focused on the analysis of electromagnetic scattering from dielectric objects. The algorithms used for calculating the scattering fields of dielectric target are analyzed, including traditional surface integration method. Starts with the volume integral equation, the relationship between total field, incident field and scattering field of weak scattering medium is given by introducing in the Born and Rytov approximation that were used for inverse scattering problem before. The integral equation of scattering field is simplified with these approximate conditions. Finally, the calculation method of electromagnetic scattering by weak scattering medium in half space is given with the application of half space green’s function.3. Based on the study of the method used for calculating the radar cross section of cavity-structure, re-derived the formula for numerical integration in view of the limitations of Fourier transformation applied in shooting and bouncing ray method. Then combined with the GRECO method and equivalent edge currents method.etc, hybrid method is applied to the RCS calculation of the composite conducting and dielectric objects with open cavities effectively based on the scattering center theory.4. Interpolation method based on the amplitude-phase detached technique is extended to forcast the wideband electromagnetic fields scattering from complex targets in half space. Primary phase factor of the induced surface currents in half space is extracted and dealed separately due to its characteristic that is highly dependent on frequency variation in high frequency range. And the remaining term, which is a smooth function of position and frequency, can be calculated by employing the best uniform approximation theory throughout the frequency band given. Then the half-space Green’s function was combined to calculate the electric、magnetic vector and scalar potential function respectively, thus obtain the scattering fields. Finally the wideband radar cross section of the targets in half space at any frequency within the given frequency range can be obtained.