Near-field Scattering Of Complex Target And Its RCS Extrapolation

The research on electromagnetic scattering characteristics of complex targets is becoming more and more urgent.The theoretical analysis method,the accurate and fast numerical simulation technology and the advanced experimental measurement technology have become the main research methods.For electrically large complex targets such as ships,combat vehiclesandaircraft,research on the near/far-field scattering and radar cross section(RCS)extrapolation from the near-field scattering has become an important research topic for the target detection and recognition,stealth and anti-stealth,electronic warfare,and it has important theoretical significance and application value.In this dissertation,the theory,simulation and application of near/far-field electromagnetic scattering and far-field RCS extrapolation are studied.The main works are as follows:(1)Theory and simulation of near/far-field electromagnetic scattering of complex targets using high frequency methods.The geometric model of complex targets is established by the combination of some basic shapes,such as polyhedron,disc,sphere,cone,and NURBS surface.The electromagnetic scattering modeling methodis established with physical optics method,impedance boundary conditions and ray tracing method.The simulating method ofnear/far-field electromagnetic scattering of complex target is implemented.By comparing the simulation results of spheres,plate,dihedral/trihedral cornerswith the theoretical values and results of other literatures,verified the correctness of our methods.(2)The theory and algorithmsof the far-field RCS extrapolation fromnear-field electromagnetic scattering of complex targets.The basic principles and calculation methods of the RCS extrapolation based on Inverse Synthetic Aperture Imaging are analyzed,and the performance of several common extrapolation algorithms,such as Huygens algorithm,Hankel algorithm and CNFFFT algorithm,are compared.A method of determining the extrapolation coefficient of RCS by using the metalsphere calibration method is proposed,which is applied to the Huygens algorithm and the Hankel algorithm.The simulation results show that:the extrapolating results of metal plate and metal cube are consistent with the real far-field RCS results;for the metal dihedral,the extrapolating results has mistaken in certain angle range duo to presence of secondary electromagneticscattering;the results of a extrapolation of the ship model with the direct calculation of the far-field,are very close in each angle,and the range of error is under the requirement of navy accuracy standard of calculating RCS.(3)Design,simulation and fabrication of single-/dual-/triple band metamaterial absorbers.By loading the cut wires in the square ring,single-/dual-/triple band metamaterial absorbers are realized.The absorbance reached 99.5%in 4.70GHz for single-band condition,and the absorbance of 98.75%and 97.64%at 4.44GHz and 8.55GHz,for dual-band absorber.The triple-band absorber achieved the absorbance of 96.94%,97.91%and 94.83%at 4.48GHz,7.81GHz and 14.05GHz,respectively.According to the single-band metamaterial absorber,the relationship between the resonance frequency and the structure size of the periodic cell is derived.The experimental results agree well with the simulation.(4)Based on the equivalent medium theory,the method to calculate the electromagnetic scattering of coated targets is presented.After the effective electromagnetic parameters of metamaterialsare retrieved from the scattering parameters of metamaterial(S parameter),the near/far-field scattering characteristics and RCS extrapolation can be analyzed by the homogeneous dielectric coating theory,which provides a new way to calculate the electromagnetic scatteringof target coated with metamaterial.Using this method,the near/far-field scattering and RCS extrapolation simulation results of dihedral in different conditions show that when there are multiple scattering case,Hankel algorithm extrapolation is effective in some range of angles,but is quite different in other range.The results also show that the Huygens algorithm is no longer applicable under this scenario.(5)A highly practical application of the electromagnetic scattering and RCS extrapolation system(ESEE)is developed.The software platform integrates the research achievements of this thesis,and its functions including the geometric modeling and electromagnetic modeling of the complex target coated waveabsorbing material,analysis and calculation of near/far-field electromagnetic scattering characteristics and RCS extrapolation.ESEE has finished the software copyright registration,and has been applied in many projects.