【作者】 孙博；

【导师】 邓维波； 邱景辉；

【作者基本信息】 哈尔滨工业大学 ， 信息与通信工程， 2010， 博士

【摘要】 超宽带技术是当前国际上一项蓬勃发展的热门技术,超宽带天线作为超宽带系统的重要组成部分之一,如何能够更好地为超宽带系统提供强有力支撑,已成为一项极具挑战性的课题。与此同时,在现代通信、雷达及无线监测与管理等应用领域,除了要求天线具有超宽带特性外,对于天线高增益特性也提出了更高要求。为了更好地满足上述两方面实际应用需求,本文将对基于TEM模的高增益超宽带天线进行深入研究,以期为高增益超宽带天线领域的科研工作探索出一些新思路和新方法。本文首先对超宽带天线国内外研究现状进行综述;其次,对超宽带天线的基本概念及理论进行简要介绍,明确了衡量超宽带天线性能的各项参数。在此基础上,重点对基于TEM模的高增益超宽带天线进行研究。作为超宽带面天线关键部分的超宽带馈源,其超宽带及高增益特性直接决定了超宽带面天线的相应特性。为此,对基于TEM模的超宽带馈源进行了详细研究。众所周知,TEM喇叭天线具有超宽带特性,但作为馈源时,会对面天线的电磁辐射造成遮挡,从而降低面天线增益。研究表明,TEM喇叭的表面电流主要分布在三角金属片两侧边缘。因此,可仅保留其表面电流集中的区域,从而形成了TEM模四线馈电臂超宽带馈源。与TEM喇叭馈源相比,采用TEM模四线馈电臂馈源的面天线阻抗特性无较大变化;并且,由于遮挡效应的减小,天线增益有了较大提高。在此基础上,研究了倒三角形、三角形和梭形三种基本的馈电臂形状对天线阻抗特性的影响,为超宽带抛物面天线馈源的设计与优化提供了理论基础。对基于TEM模的超宽带抛物面天线进行了深入的研究,设计了三角形、梭形、指数型和复合型四种类型的馈电臂。首先,根据解析法设计了三角形馈电臂超宽带抛物面天线,其具有很宽的阻抗带宽和较高的增益,天线的工作频带为1.5~9.5GHz ,带内增益为10.2~23.9dB ,口径效率为0.53~0.69。其次,为减小三角形馈电臂末端的电流聚集,将馈电臂设计为梭形,同时对馈电臂间夹角进行了优化,天线的工作频带扩展至1.1~18.4GHz,带内增益为11.3~28.4dB,与采用三角形馈电臂结构的超宽带抛物面天线相比,平均增益提高了3dB,口径效率达到0.7~0.76。接下来,为进一步优化天线性能,提出了指数型馈电臂结构。采用这种馈源结构的超宽带抛物面天线的工作频带可达1.05~20GHz以上,在工作频带内最大增益达到28.9dB,口径效率达到0.71~0.77。最后,为改善天线的低频特性,又提出了复合型馈电臂结构,将指数曲线与线性项相结合构成新的馈电臂边界形状。采用此馈源结构的抛物面天线,其下限工作频率由1.05GHz下降至0.7GHz,降低了33.3%,从而有效拓展了天线的低频端工作频率。而通过对馈电臂末端进行电阻加载处理,可继续降低天线的下限工作频率,通过选择合适的加载阻抗,最终使天线的工作频率下限降为0.3GHz,实现了良好的低频拓展效果。除了将抛物面天线作为高增益超宽带天线形式进行重点研究外,本文还对基于TEM模的超宽带透镜天线进行了探讨。在TEM喇叭的口径处加入介质透镜即构成了TEM模超宽带透镜天线,此结构可以较大程度地弥补和缓解相位差带来的色散现象,从而能够有效增强天线的远场辐射,提高天线增益。分别设计了双曲面透镜、椭球面透镜、球面透镜以及改进的双层介质球面透镜等几种天线形式。双曲面透镜和椭球面透镜在保持TEM喇叭超宽带阻抗特性的基础上,将天线的高频增益提高了10dB以上。为进一步扩展天线工作频带,提出了球面透镜以及改进的双层球面透镜设计,其工作带宽均可达到0.76~20GHz;尤其是由两种不同介质构成的双层球面透镜,在实现天线超宽带性能的前提下,可以明显改善高频端增益,与单层球面透镜相比,天线增益最大可提高5.5dB,这种分层介质的设计思想在实际应用中具有很高的参考价值。本文对基于TEM模的高增益超宽带天线进行了深入地研究,提出了几种天线模型,并进行了实验研究。本文提出的设计思路和设计方法具有良好的实际应用价值,可以为今后高增益超宽带天线的设计提供借鉴与参考。更多还原

【Abstract】 Ultra-wideband is an international hotspot technology developing very rapidly at present. As one of the important components of the ultra-wideband system, ultra-wideband antenna has been a challenging research topic. Meanwhile, higher requirements for not only the ultra-wide band characteristics but also the high gain characteristics of the antenna are put forward when it comes to modern communications, radar and wireless monitoring and management applications.In this dissertation, the international research situation is summarized firstly. Afterward, the fundamental conceptions and theory is introduced briefly, and the performance parameters of the ultra-wideband antenna are defined. On this basis, the high gain ultra-wideband antenna based on TEM mode is researched detailedly.As the key component of the ultra-wideband antenna, the ultra-wideband characteristic and high gain characteristic of the feed will decide characteristics of the antenna. Therefore, the ultra-wideband feed based on TEM mode is studied in detail. The TEM horn has great ultra-wideband characteristic, however, when it is used as the feed of a paraboloid antenna, the metal plate will shadow the electromagnetic radiation hence decreasing the gain. Researches show that the surface current distribution of the TEM horn is mainly at the side edge, thus holding the concentrated region of the surface current will form the TEM mode four wirelike feed arms model. Compared with feeding by TEM horn, the paraboloid antenna with TEM mode four wirelike feed arms can maintain the good impedance characteristic, while the antenna gain is quite higher owing to the reduction of the blockage Then, three forms of feed arms are researched respectively, and the effect of different structure on antenna impedance performance has been given, which can be the theoretical basis for the design and optimization of feed arms.The ultra-wideband paraboloid antenna based on TEM mode is studied systematically, and design methods of four types of feed arms are proposed. The ultra-wideband paraboloid antenna with triangular feed arms can be designed by analytic means, and it has obtained good impedance and radiation characteristics. The operating frequency range of the antnna is 1.5 to 9.5GHz; and the gain is 10.2~23.9dB within the band, and the aperture efficiency is 0.53~0.69. In order to reduce the current at the end of triangular feed arms, fusiform feed arms are designed, and meanwhile, the angle between feed arms is optimized. The operating frequency range of the antenna can be extended to 1.1 to 18.4GHz, and the gain is 11.3~28.4dB within the band. The average gain is 3dB higher than that with triangular feed arms, and the aperture efficiency is 0.7~0.76. To further optimize the antenna performance, exponential tapered feed arms are proposed. This structure can broaden the operating frequency range of the antenna to 1.05 to 20GHz, and the maximum gain is 28.9dB within the band, and the aperture efficiency is 0.71~0.77. Furthermore, in order to improve the low-frequency characteristic, composite tapered feed arms are presented, which is formed by adding a linear term to the expression of exponential curve. The lowest operating frequency of the antenna is expanded to 0.7GHz, which is 33% lower than that of the exponential tapered feed arms, thus the lowest operating frequency is decreased effectively. In addition, further reduction of the lowest operating frequency can be realized by loading resistances at the end of feed arms. And the low limit frequency of the antenna has been decreased to 0.3GHz, and the effect of the low-frequency expansion is obviously.Besides the paraboloid antenna, the lens antenna can also be employed to be the high gain ultra-wideband directional antenna.The dielectric lens attached at the aperture of the TEM horn can compensate and eliminate the chromatic dispersion brought by the phase contrast, and can enhance the far field radiation effectively hence increasing the antenna gain. The hyperbolic lens, meniscus lens, single layer spherical lens, and double layers spherical lens are designed respectively. Compared with the TEM horn antenna, both of the hyperbolic lens antenna and the meniscus lens antenna can increase the antenna gain over 10dB, while the ultra-wideband impedance characteristic and directionality are kept very well. The spherical lens antenna can further extend the antenna bandwidth to 0.76 to 20GHz, and moreover, the double layers spherical lens will improve the gain of high band obviously, and the maximal increased gain can be 5.5dB. The design idea of stratified dielectric has good value to the practical application.The main purpose of this dissertation is to research and design the high gain ultra-wideb antenna based on TEM mode. Several antenna models are proposed , and experiments are preformed. The design ideas and methods presented in this dissertation have good value to practical application, and will provide consultation for the design of high gain ultra-wideband directional antenna in the future.更多还原