【作者】 郑秋容；

【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， 2007， 博士

【摘要】 微波光子晶体,也称为电磁带隙结构(Electromagnetic Band-Gap:EBG),是一种具有频率禁带的新型周期结构。本文主要针对微波光子晶体的带隙特性及其在微波天线和隐身材料中的应用进行了研究。首先建立分析微波光子晶体结构的理论模型和数值仿真工具,研究对象为以微带基片为载体的微波光子晶体结构。利用Floquet定理,无限大周期结构可以简化为一个周期单元来计算。数值仿真方法采用周期格林函数与矩量法相结合,采用谱域导抗法得到微带结构的全三维并矢格林函数。利用所建立的数值仿真工具,对几种微波光子晶体结构进行了计算,包括平面微波光子晶体以及加载覆盖层光子晶体的带隙特性。各部分的主要研究内容为:(1)平面型光子晶体考虑了方形贴片光子晶体的谐振特性,主要考察了单元尺寸、缝隙尺寸、基板厚度和介电常数、覆盖层的厚度和介电常数以及过孔半径等不同参数对谐振特性的影响,提出了一些新型的紧凑的平面型微波光子晶体——交指型结构和螺旋型结构。(2)针对某些天线系统设计中需要得到双频段或多频段带隙,本文计算了具有分形特征的二维金属柱EBG结构,获得双频段的频率带隙甚至是新的全局带隙,并且总结了它们的工作特性和分形结构之间的关系。(3)研究了光子晶体在微波天线以及天线阵列中的应用。主要研究了高阻表面在波导缝隙天线中的应用,包括波导端头缝隙天线、16元单脊波导缝隙天线阵以及16元非对称单脊波导缝隙天线阵。研究表明,光子晶体的引入可以有效地改善天线和天线阵列的特性,主要体现在可以提高天线主瓣增益、降低后向和侧向辐射电平上以及减小天线单元和天线阵列间的耦合。对高阻表面在相控阵天线中的应用进行了初步的探讨。利用高阻表面的频率带隙抑制相控阵天线单元间的互耦,改善了相控阵天线的宽角阻抗匹配,消除了相控阵天线的扫描盲点问题,从而改善天线的扫描特性。在连续波雷达中收发天线阵之间的隔离度是一个非常重要的指标。在连续波雷达的实际设计中不能将雷达收发天线的间距设计的过大也不能过小,因为收发天线之间间距如果太小,发射天线所发射的电波就会有一部分直接进入接收天线。针对这一问题本文利用光子晶体材料的电磁带隙特性,有效地解决长期困扰连续波雷达设计的收发天线互耦问题,提高收发隔离度,获得了互耦系数减小15 dB的效果,增加了连续波雷达的探测能力,(4)对光子晶体在吸波材料中的应用进行了初步研究。利用光子晶体的同相反射特性作为人工磁导体,代替传统的电损耗Salisbury屏的间隔层,降低了整体厚度,同时又保持电损耗的稳定性能。并将这种新型的由光子晶体制作的吸波材料成功地应用于波导端头缝隙天线,和非对称单脊波导缝隙天线阵,使这些天线和天线阵在增益衰减较少的情况下,雷达散射截面(RCS)得到了较为明显的减缩。更多还原

【Abstract】 Microwave photonic crystals (MPC), also referred as electromagnetic bandgap(EBG) materials, are periodic structures characterized by the existence of frequency bandgaps. The dissertation focuses on the electromagnetic characteristics and its application in microwave antenna.At first we establish theoretical model and numerical simulation method that are constructed in the microstrip structures. The infinite periodic structure is reduced to one single cell by applying Floquet theorem. The numerical simulations are performed using periodic Green’s functions plus the method of moments (MOM) and the whole dimensional dyadic Green’s functions are obtained by using spectral domain immittance approach (SDI).Using the above simulation tools, several kind MPC structures have been analyzed, including the planar MPC and the bandgap characteristics of MPC with a cover layer. The primary work is as follows:(1) In planar MPC, the cells with square patches have been mainly studied. Some parameters which can affect the resonant performance of the MPC have been studied, including cell size, gap width, thickness and dieletric constant of substrate and that of cover layer, and radius of via. Some new MPCs, such as interdigital MPC, and spiral MPC, are provided.(2) Aimed at the dual/multiple bandgap in some antenna system design, 2-D metal cylinder EBG structure with fractal characteristics is computed and dual frequency bandgap even new complete bandgap are obtained. At last the relationship between their working characteristics and the fractal structure is summarized(3) The photonic crystals (PC) have been applied in microwave antennas and antenna arrays. The high impedance surface (HIS) has been mainly used in waveguide slot antennas including waveguide end-slot antenna, sixteen-element single ridged waveguide slotted antenna array and sixteen-element asymmetric single ridged waveguide slotted antenna array. The results show that the PCs can improve the characteristics of antennas and antenna arrays. The gain of main lobe has addition, the radiation levels of back/side lobes decrease and the mutual coupling between the antenna elements or arrays can be reduced. The application of the HIS in phased arrays is investigated basically. The HIS is used to suppress the mutual coupling between the phased array elements and the results show that the HIS can improve the scan characteristics of phased array through ameliorating the wide-angle impedance matching and eliminating the scan blindness.Isolation of receiver-radiation antenna arrays in Continuous-Wave Radar is an important parameter. In the practical design of Continuous-Wave Radar, the space between receive and radiation antenna should not be too large and not be too small,either. If the space is too small, there is a problem that the power from radiation antenna will radiate directly into receive antenna. The application of EBG bandgap can solve this problem effectively. By using EBG can reduce the mutual coupling and promote the isolation. The measured results show that the mutual-coupling coefficient reduced 15dB, improved the detective ability of Continuous-Wave Radar.(4) The applications of PC in absorbing materials have been studied. Because of the in-phase characteristics, the periodic structures can be used as artificial magnetic conductor (AMC) and substituted for the spacer of the traditional electric Salisbury screen in order to reduce the entire thickness and preserve the stability of the traditional electric Salisbury screen. The new absorbing materials which are made of PC are successfully used in waveguide end-slot antenna and asymmetry single ridged waveguide slotted antenna array. The testing results suggest that the new absorbing material can obviously reduced the Radar Cross Section (RCS) with little attenuation of these antennas’ gain.更多还原