Research On Simulation Method Of FSS Electromagnetic Characteristics Based On Integral Equation

With the development of science and technology and military,stealth technology has gradually become a research hotspot.As an important part of stealth structure,frequency selective surface(FSS)has been paid much attention by engineering and academic circles.FSS consists of two-dimensional periodic pure metal arrays or metal-medium hybrid structures containing a dielectric substrate.It is essentially a spatial filter with selective transmittance to electromagnetic waves of different frequencies.The characteristics of band pass and band resistance are presented according to the aperture and the type of patch.At present,the engineering research of FSS focuses on the irregular structures such as finite size,curved surface and conformal,to adapt to more and more complex applications.However,the complex FSS is not only difficult to model geometrically,but also lacks suitable electromagnetic analysis methods.the design process of FSS is often very difficult and time-consuming.In order to guide the design of frequency selection structure more accurately and quickly.This paper presents a general topology and analytical modeling method for FSS.Based on the theory,the numerical simulation method of integral equation is improved.The problem of low precision and low efficiency of FSS solution is solved.Firstly,this paper introduces the special analysis method of FSS and the common algorithm of numerical calculation.The advantages and disadvantages of different methods are compared and the integral equation is determined.After that,three kinds of integral equations and their applicable scope are expounded in detail.I introduce the solving process of integral equation method of moments(MOM)and acceleration algorithm,including RWG basis function,SWG basis function and multilevel fast multipole algorithm(MLFMA)accelerating matrix-vector multiplication.Then,in order to comprehensively understand the electromagnetic characteristics of FSS,this paper analyzes in detail the commonly used influence factor of FSS,including unit type,arrangement mode,medium loading and incident angle.I studied separately the infinite period FSS,finite large plane FSS,surface and conformal FSS respectively.I proposed the modeling methods of various complex FSS and compared the transmission reflection characteristics of different FSS through simulation.Then I studied the method of improving the solution precision of integral equation.I introduce the problem of frequency response curve deviating towards high frequency when calculating FSS by VSIE.It is proved by theoretical derivation that the normal boundary condition of electric displacement vector and the equation of current continuity are implicit in the solution of integral equation by MOM.The fundamental reason of frequency deviation is that the tangential component of electric field is not accurately described.The solution precision is improved by imposing tangential boundary conditions.Then,the quadrilateral-hexahedron mesh and quasi-orthogonal basis function are studied and the process of singularity processing is derived in detail.It is found that there is no frequency deviation and it has good convergence,which is more suitable for solving FSS structure than triangle-tetrahedron mesh.Finally,I studied the domain decomposition algorithm of integral equation(IEDDM).FSS was divided into different regions for multi-scale subdivision.Each region was calculated separately and the boundary current continuity was ensured by internal penalty constraints.The algorithm greatly reduces the memory overhead and solves the problem of FSS calculation in large size.In order to quickly analyze the monostatic RCS of FSS,I proposed a generalized minimum residual algorithm(GMRES)with multiple right end terms.In order to improve the iterative convergence of biconjugate gradient stabilized method(BICGSTAB),I study the two threshold incomplete LU decomposition preconditions(ILUT(p,?))for MLFMA.The whole research forms a closed loop of geometric modeling,integral equation,boundary condition,basis function and singularity treatment,region decomposition and iterative algorithm.I proposed a complete analysis method and wrote a computer program.The method described in this paper greatly simplifies the research difficulty of FSS.It plays a guiding role in the design of complex FSS and has practical engineering significance.