【作者】 闫敦豹；

【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， 2006， 博士

【摘要】 近几年来,软硬表面(soft and hard surfaces)、光子晶体(photonic crystals)、电磁带隙结构(electromagnetic band-gap stzuctures)、双负材料(double negativematerials)或称左手材料(left-handed materials)以及人工磁导体(artificial magneticconductors)等人工电磁材料开始博得愈来愈广泛的关注,原因在于它们均具有在自然界中并不存在的但极具价值的电磁特性。这些结构或材料被学界称为超材料(metamaterials),而它们所具有的奇特的电磁特性已经在微波领域开始得到广泛的应用,用以实现高性能天线及微波器件。其中人工磁导体在天线应用特别是低剖面天线实现上具有无与伦比的优势与潜力,有着巨大的应用前景,具有极高的研究价值。本文即针对人工磁导体材料进行了深入研究,发现了其另一个奇特的对入射波的极化转换特性,成功设计了更具应用价值的紧凑型结构,并在一些经典天线上实现了成功应用。本文首先研究了人工磁导体最基本的表面波带隙与反射相位带隙特性,全面详细地分析了所有的结构参数对带隙特性的影响,并得出了相应的结论。研究了非对称AMC结构(包括矩形结构与缝隙加载结构)的反射相位带隙与入射波极化的关系,发现反射相位带隙只与AMC结构在入射波极化方向上的电尺寸有关,而与相垂直方向上的电尺寸基本无关。进一步研究发现AMC结构单元的中心位置的过孔的存在与否并不影响其反射相位带隙,故在对矩形AMC结构的基础上提出了一种结构更为简单的一维条带型AMC结构。研究了非对称AMC结构(包括矩形结构、缝隙加载结构及条带型结构)的方向性表面波带隙特性,发现与传播方向同向上的单元电尺寸决定着带隙的最低频率,也就是可传输TM模表面波的最高频率,而与传播方向相垂直方向上的单元电尺寸决定着带隙的最高频率,也就是可传输的TE模表面波的最低频率。研究了偏置过孔AMC结构的反射相位带隙与入射波极化的关系,发现对线极化的入射波,反射波在不同的频率呈现不同的极化状态,可以分别为与入射波极化相同的线极化、左旋圆极化、与入射波极化相垂直的线极化及右旋圆极化等,我们称之为极化转换特性,并对这种特性在隐身技术及实现天线极化转换上的应用进行了可行性分析及有意义的探索。对简单目标可以有效的降低其共极化的雷达散射截面,而在实现天线的极化转换上可以根据需要将简单线极化馈源发射的电磁波经过抛物面反射后转换为左旋或者右旋圆极化波。针对小尺寸是现代微波电路及天线发展的必然趋势,为使AMC结构得到更为广泛的应用,在对其基本特性研究的基础上,本文成功设计了三层结构、十字形结构、缝隙加载结构以及交互嵌入式结构等几种紧凑型AMC结构,并分析了他们的反射相位带隙特性及表面波带隙特性。其中提出的三层结构、十字形结构、缝隙加载结构以及交互嵌入式结构分别可降低AMC结构单元尺寸达50%、15%、30%、70%左右,其中交互嵌入式结构是目前公开发表的相关技术中尺寸最小的结构。利用AMC结构的表面波抑制特性,将AMC结构成功的应用于普通微带天线、圆极化微带天线以及微带天线阵列。在普通微带天线应用上分别设计了工作于C波段及蓝牙通信频段的两种天线,并提出了一种改进的菱形栅格的AMC结构,它的应用可以降低天线背瓣达15dB,同是提高增益0.9dB,明显优于普通的正方形栅格及六边形栅格。进而分析了AMC结构与天线之间的距离以及AMC结构的层数等参数对天线性能的影响,并得出了相应的结论。在圆极化微带天线上应用AMC结构,除提高天线增益、降低背瓣辐射外,还能增加频率上的轴比带宽。在天线阵列上使用AMC结构则可以有效的降低天线单元之间的表面波传播造成的耦合,提高天线阵列的性能,增大扫描阵列的扫描范围。利用AMC结构的反射相位带隙特性成功实现了具有低剖面特性的水平线天线及平面倒F天线。其中水平线天线的整个纵向尺寸仅为3.5mm,且能形成有效的辐射,这在普通金属表面上是不可能实现的。平面倒F天线是目前无线通信中手持终端设备广泛使用的天线,通过应用AMC结构可以有效的降低天线的纵向尺寸或平面尺寸,为平面倒F天线的使用提供了更为有利的条件。更多还原

【Abstract】 In recent years, there has been increasing interest in artificial electromagnetic materials, such as soft and hard surfaces, photonic crystals (PCs), electromagnetic band-gap (EBG) structures, double negative (DNG) materials or left-handed materials (LHMs), and artificial magnetic conductors (AMCs), because they all have novel electromagnetic features which may not occur in nature. These structures are broadly classified as metamaterials and their novel electromagnetic features have led to a wide range of applications in microwave fields to achieve high performance antennas and microwave components. Of all these artificial electromagnetic materials, AMCs have incomparable advantage and potential in antenna application, especially in achieving low profile antenna. Therefore, AMCs have expansive prospect in antenna application and are greatly worthy of research. In this dissertation, an in-depth study on AMCs is performed, and a unique polarization converting property of incident plane wave is found. Moreover, some compact structures with more applied value are designed and applied on classic antennas successfully.Firstly, two basic properties of surface wave band-gap and reflection phase band-gap are studied in this dissertation. The effects of all structure parameters on band-gap are analyzed, and some corresponding conclusions are obtained. For Asymmetric AMC structures, including rectangular and slotted structures, relation of reflection phase band-gap and incident wave polarization direction is studied. It is found that the reflection phase band-gap is only depend on the electric size of AMC cells in the direction of incident wave polarization, and is independent on the electric size in the perpendicular direction. In further, it is found the reflection phase band-gap is independent on the central vias of AMC structure. And so, a simpler strip type AMC structure is brought forward based on rectangular structure. Directional surface wave band-gap property of asymmetric AMC structures is studied, including rectangular, slotted and strip type structures. It is found the lowest frequency of band-gap, which is the highest frequency of propagated TM mode surface wave, is determined by the cell electric size in the direction of propagation. And the cell electric size in the perpendicular direction determines the highest frequency of band-gap, which is also the lowest frequency of propagated TE mode surface wave.The relation of incident wave polarized state and reflection phase band-gap of AMC structure with offset via is studied. For linear polarized incident plane wave, the polarization state of reflected wave can be linear polarization (the direction is parallel to incident wave), left-handed circular polarization, linear polarization (the direction is perpendicular to incident wave), right-handed circular polarization, which is termed polarization converting property. Feasibility analysis of application on stealth technique and significative research on achieving polarization converting of antennas are performed. For simple targets, with application of AMCs, there co-polarization radar cross section (RCS) can be decreased greatly. After reflected by paraboloid with AMC, linear polarized wave transmitted by feed source can be converted to left-handed or right-handed circular polarized plane wave with demand.Small size is the development trend of modern microwave circuit and antenna. Therefore compact AMCs can be applied more extensively. In this dissertation, at the foundation of basic property study, some compact AMC structures are designed successfully, including three-layer structure, cross shape structure, slotted structure and inter-embedded structure. There reflection phase band-gap and surface wave band-gap are studied, and there element size can be decreased about 50%, 15%, 30% and 70% respectively. In these structures, the inter-embedded AMC structure is the smallest one in all structures published in public.Utilizing its suppressing propagation of surface wave, AMCs are applied on linear, circular polarization microstrip antenna and microstrip antenna array successfully. Two linear polarization microstrip antennas are designed, which work at C-band and Bluetooth communication band respectively. With the application of a novel triangle grid AMC structure, back lobe of antenna is decreased about 15dB, and the gain is increased about 0.9dB, which is superior to antennas with square or hexagon AMC applied. In further, the effects of some parameters on antenna performance are analyzed, including distance between AMC and patch, the number of AMC layer, and some corresponding conclusions are obtained. With the AMC applied on circular polarization patch antenna, not only the gain is increased and the back radiation is decreased, but also the axial ratio band width vs frequency can be increased. By suppressing the propagation of surface wave, applying AMC on antenna array can decrease the mutual couple of antenna elements, and improve antenna performance, and enlarge scan angle of scanning antenna arrays.Using in-phase reflection of AMCs, low profile horizontal wire antenna and plane inverted F antenna built on AMCs are achieved successfully. Horizontal wire antenna with AMCs can radiate effectively, and its height is only 3.5mm, which is impossible on metal plane. Plane inverted F antennas are applied extensively on handle terminal equipments in wireless communication. The application of AMCs on PIFA can decrease longitudinal size or planar size of antenna, which is advantaged in actual application.更多还原