Electromagnetic Scattering Analysis Of Multilayer Dielectric Targets And Dielectric-coated Metallic Targets

Due to light weight and high strength, thin dielectric materials have been increasingly used in practical engineering. In particular, stratified thin dielectric materials can be used to produce the radome, heat isolation cover, and radar absorbing structure, etc. However, numerical modelings of the dielectric electromagnetic scattering have faced technical challenges of huge unknowns and bad iteration convergence for a long time. Facing the above problems, this paper is written from the two aspects of modeling method of the thin dielectric and basis functions, and a series of research work is done in solving electromagnetic scattering problems of multilayer thin dielectric objects and multilayer thin dielectric-coated metallic objects accurately and rapidly.Firstly, the theoretical basis and numerical simulation of the integral equation method have been introduced in this paper. It gives an overview of the surface integral equation, volume integral equation and volume surface integral equation methods. In addition, the thin dielectric sheet(TDS) approximation method based on the volume integral equation method is introduced in detail. On the basis of the above work, the numerical simulation and key technologies of the method of moments are introduced systematically. This section studies the steps of solving electromagnetic scattering problems by using numerical methods.Secondly, the modified single-layer TDS approximation method which can be applied for single thin-layer dielectric-coated metallic targets is studied. Considering the effect of Green’s functions’ accuracy on integral results, we adjust the values of Green’s functions with an effective controlling of the computational amount. So the values of Green’s functions are more close to true values. Meanwhile, the solvable thickness is increased with a given accuracy.Based on the modified single-layer TDS model, the modified multi-layer TDS approximation method is presented. Corresponding recurrence formulae are derived also. The modified multi-layer TDS approximation method can be applied for multilayer thin dielectric and multilayer thin dielectric-coated metallic targets. In the modified multilayer TDS model, the volume current in each thin layer can be decomposed into tangential and normal components according to different directions of the currents. The tangential distributions of tangential and normal volume components are expanded by CRWG and pulse basis functions, respectively. And the normal distributions of normal current components can be obtained using recurrence formulae which are derived according to the Maxwell equation. In order to save the number of unknowns, the original multi-layer TDS method describes normal currents using a one-way recursive formula to reduce the number of normal unknowns. However, the one-way recursion will include a large recursive error for a thicker medium. The modified multi-layer TDS method improves the recursion formulae of normal currents, making it become a two-way recursion. That is to say, the formulae work in the upward and downward directions at the same time. The two-way recursion can improve the accuracy of solving the same problem. In the premise of a given error tolerance, the method can increase the thickness of thin layers which can be modeled.Aimed to efficiently analyze the electrically large target, we have combined the modified phase extracted(MPE) basis functions with the modified single-layer TDS method, and phase extracted(PE) basis functions with the modified multi-layer TDS method, respectively. The electromagnetic scattering models of electrically large single-layer thin dielectric-coated targets and multilayer thin dielectric targets are further simplified. When the dielectric coating of a dielectric-coated metallic target is very thin, the tangential current component can be seen as zero according to the PEC boundary condition. Then the normal current component varies with the induced surface current. By the use of MPE basis functions, it can analyze the concave and convex metallic targets rapidly and accurately. On the other hand, a multilayer thin dielectric target has the property of guiding waves in a multilayer thin waveguide. Therefore, the propagation of the volume currents along the tangential direction can be considered as a traveling wave distribution. Using PE basis functions which only describe the traveling wave property of volume currents, the multilayer thin dielectric target will be analyzed rapidly and accurately.Aimed at the electromagnetic scattering modeling of sandwich radomes, the stratified volume integral equation method is proposed in this paper. For sandwich radomes, the dielectric layers are no longer all thin layers, where the thin and thick layers both exist. For example, the A-sandwich radome has a structure of two high-density thin skins and one high-transmission thick core. The equivalent stratified model is presented according to the specific structure of the sandwich radome. The criteria of how to select unknowns is made by considering the thickness of the sandwich radome, so that the number of unknowns is minimized.Finally, as a typical application of the proposed methods in this paper, the integrated theoretical modeling and numerical analysis of the near space hypersonic vehicle, the plasma sheath, and the vehicle antenna is studied. When the frequency of an incident wave is up to the microwave frequency band, the near space hypersonic vehicle is a typical electrically large target. During the high-speed flight, a lot of gas around the vehicle produces great plasma at high temperatures on the surface of the vehicle. Compared with the electrical size of the vehicle, the plasma sheath is thin. In this paper, the plasma sheath is equivalent to the multilayer medium. Therefore, the hypersonic vehicle covered by the plasma sheath can be seen as a thin dielectric-coated metallic target. The volume surface integral equation method, modified single-layer TDS method, and modified multi-layer TDS method can be used to efficiently analyze electromagnetic scattering properties of the hypersonic vehicle covered by the plasma sheath. Due to a few unknowns required in the modified single-layer TDS method, and modified multi-layer TDS method, it is easier to achieve the integrated efficient analysis of the near space hypersonic vehicle, the plasma sheath, and the vehicle antenna.