【作者】 李有权；

【导师】 袁乃昌；

【作者基本信息】 国防科学技术大学 ， 电子科学与技术， 2010， 博士

【摘要】 电磁带隙(EBG)结构是一种新型的人工电磁材料,已经在微波领域得到广泛的研究与应用,用以实现高性能天线及微波器件。但是EBG结构的电磁散射特性的研究没有引起足够的重视,EBG结构用于隐身尤其是天线隐身的研究还很少。本文主要对电磁带隙结构在目标隐身方面的应用进行研究。介绍了电磁带隙结构的数值分析方法。我们根据不同的需要选择不同的分析方法。选择有限元法分析EBG结构的能带特性,选择FDTD方法分析EBG结构的同相反射特性。简要介要了两种方法的基本原理,并给出实际计算实例。深入研究了EBG结构的电磁特性。重点分析了电阻加载EBG结构的表面波特性。采用RLC电路对加载电阻后的EBG结构的表面阻抗可以进行等效,并采用传输线模型对其带隙特性进行了分析。采用LC等效模型对EBG结构的表面阻抗进行建模,给出反射相位的计算公式。最后研究了EBG结构的表面波带隙及反射相位的关系,并通过实验进行验证。研究利用EBG结构改变目标散射特性。理想磁导体(PMC)和理想电导体(PEC)的反射相位相差1800,将PMC和PEC结构组合在一起,利用相位的差异改变平面结构的散射特性。首先分析了简单组合结构的散射特性,采用软件对其单站RCS进行仿真并与测试结果进行了对比,PEC和PMC组合结构能有效降低后向散射,但是对入射波极化方式敏感。在此基础上提出了棋盘结构,分析棋盘结构的散射特性,给出了影响棋盘结构RCS减缩效果的两个因素:相位差及单元尺寸。最后采用不同尺寸的EBG结构实现了宽带棋盘结构。深入研究了基于EBG结构的超薄吸波材料。利用EBG结构的同相反射特性,可以实现超薄吸波材料,其设计原理与Salisbury屏吸收原理一致。采用集总参数等效模型对吸波材料进行建模,给出了吸波材料的设计方法。研究发现吸波材料的吸波带宽是由EBG结构的同相反射相位±600的频带决定的,在焊接电阻过程中引入了寄生电容,导致吸波频带向低频偏移了。采用缝隙加载技术可以有效降低高阻表面的反射相位,从而有效降低吸波材料的工作频段。最后研究了基于方形环的吸波材料的吸波特性。研究了超薄吸波材料在天线阵中的应用。将吸波材料用于天线阵,可以有效降低天线的结构散射,同时保持了天线的辐射特性。在波导缝隙阵列天线及螺旋天线阵上的应用表明,天线RCS可以得到有效降低,而天线阵的辐射特性仅增益有所降低,为天线隐身提供了一种新的途径。更多还原

【Abstract】 Electromagnetic bandgap (EBG) is a novel metamaterial which has been used widely in microwave region to realize high performance antenna and microwave components. But the scattering characteristics of EBG is not in emphasis, and the researches on stealth technology of EBG especially antenna stealth is few. This thesis is focused on the application of EBG to the stealth technology.The numerical methods to analyze the EBG structure are introduced, different numerical method is chosen according to different needs, the FEM method is chosen to analyze the eigen electromagnetic modes and the FDTD is chosen to analyze the in-phase reflection characteristics. The basic principles of this two numerical methods are introduced and practical examples are given.The electromagnetic characteristic of mushroom-like EBG is researched deeply in this chapter. The mechanism of bandgap forming and in-phase reflection forming are given briefly, the research emphesis is the characteristics of mushroom-like EBG structures loaded with lumped resistors. The surface-wave propagation along the resistor loaded EBG surface is discussed using the equivalent parallel RLC circuit and then the bandgap property is analyzed using the periodically loaded transmission line model. The surface impedance of mushroom-like EBG can be modeled using LC equivalent circuit and the formulas are given. The reflection phase of EBG predicted well using equivalent model compared with the measured results. The relationship of surface wave bandgap and in-phase reflection is researched and the conclusion is verified by experiment results.The application of mushroom-like EBG on changing the scattering characteristics of planar structure is studied. There is 1800 difference between the reflection phase of perfect electric conductor (PEC) and perfect magnetic conductor (PMC). The scattering characteristics of the composite structure combined with PEC and PMC will change. At first, the scattering characteristics of simple composite structure is analysis, the monostatic RCS is simulated and compared with the measured results, the measured results show that the backscattering is reduced effectively,but it is sensitive with the polarization of incident wave. The chessboard like structure is proposed, the scattering characteristics of it are analyzed, and the factors influnced the RCS reduction of chessboard are phase difference and unit size. The broadband chessboard is proposed which is composed of different parameters EBG structure.The ultra-thin absorbing material based on the EBG is studied. The EBG has the in-phase reflection characteristic which can be used to design ultra-thin absorbing material, the design principle is the same with the Salisbury screen. The equivalent circuit model of the absorbing material is developed and the design method is given. The results show that the absorbing band of RAM is decided by the reflection phase of EBG in the range±600. The measured absorbing frequency band of RAM moved toward lower frequency than the simulated results, which attributes to the parasitic capacitance introduced by lumped resistors. The EBG patch loaded with slot will decrease the operating frequency of EBG, this method can decrease the absorbing band of RAM. Finally the RAM based on the square loops is proposed.The application of this ultra-thin RAM to antenna array is studied finally. When the RAM is used to antenna, the structural scatter of antenna is reduced effictively and the radiation performance is maintained. The applications of RAM to ridged waveguide slot antenna array and helical antenna array show that the RCS of antenna is reduced and only gain decreased 0.9dB. This provides a new direction for antenna RCS reduction.更多还原