【作者】 李萍；

【导师】 梁昌洪；

【作者基本信息】 西安电子科技大学 ， 电磁场与微波技术， 2005， 博士

【摘要】 本文针对国防急需UHF小结构、高强度、高增益和宽频带天线的情况,根据粗振子和印刷振子受电介质的影响会使谐振长度明显缩小的现象,研究了平面天线结构与电参数的关系。文中在阐述矩量法和时域有限差分法的基础上分析了平面直立天线的面电流分布。结合矩量法和镜像原理对矩形平面单极子天线的阻抗特性等参数进行了分析,并利用高频结构仿真软件(HFSS)证明了平面天线的宽带特性。文中用时域有限差分法(FDTD)分析了一般平面天线。对矩形天线开槽形成的凹形结构也进行了分析,并用HFSS仿真软件对其进行了优化。在此基础上首次提出设计一种新颖的H形平面直立印制宽带小型化天线结构。通过结构仿真形象地给出H形平面天线的带宽、增益、面电流分布以及近、远场辐射方向图形等,并比较了该天线的输入阻抗的频率特性和天线增益。 论文从展宽天线频带的理论出发,从H形平面天线的馈电问题入手,叙述了与课题相关的宽带网络基础知识。围绕宽带匹配网络的数值优化理论展开讨论,分析了如何在天线结构一定的情况下展宽天线带宽的各种网络匹配方法,特别对课题所设计的H形直立天线的馈电进行了研究。基于H形天线馈电延长线产生的散射场对天线电参数的影响,文中提出设计同轴线T形馈电接口结构,并用其等效的匹配网络在理论上证明其满足天线宽带的要求。文中用数值法分析了这种印制天线在标准同轴线馈电时的驻波和辐射功率特性。通过计算机结构仿真定量地研究了这种馈电结构对天线性能的影响。比较了标准和T形馈电结构对天线系统电参数的影响,发现改变馈电外导体宽头位置能够调节天线的谐振中心频率。通过ANSOFT HFSS仿真,给出了外导体高度变化与天线到地面空气隙间距变化对天线工作带宽和增益的影响,得到的这些结构与驻波关系曲线图对工程设计有一定的参考价值。考虑H形天线馈电凹槽的实际尺寸,在T形馈电的基础上本文还建立了一个带约束条件的目标函数。通过加入罚函数将其转化为无约束目标函数,并优化得出一组使天线匹配良好的同轴线结构外径值。按照所选优化值制作两节级联同轴线阻抗匹配器接入天线内,结果表明设计的阻抗匹配器达到了展宽天线频带宽度的目的。 文中提出的对平面H形天线加介质罩的方案,解决了车载天线的强度问题。通过高频结构仿真和对带有介质罩的H形天线的实际测试,给出了这种天线的驻波带宽、辐射功率和天线增益,并且对常用的车载鞭天线和加介质罩天线进行了通信距离的实际测试。 最后文中还针对UHF机载合成孔径雷达天线小型化、高增益和宽频带的需要,更多还原

【Abstract】 According to the characteristics of the UHF antenna used in the army, such as small size, high strength, high gain and broadband, and the phenomenon the resonance length of the thick dipole and the printed dipole be reduced obviously because of the influence of the dielectric, the relationship of the planar antenna structure and the electrical parameter is discussed. On the basis of the exposition of the method of moments and finite difference time domain method, the current distribution of the vertical planar antenna and the impedance characteristic parameters of the rectangle planar monopole antenna is analyzed, which testifies the wide-band characters of the planar antenna by utilizing the high frequency simulation software (HFSS). In this article, the finite difference time domain method is used to analyze the general planar antenna. An original structure of broadband and miniaturized H-shaped planar printed monopole antenna is designed firstly According to the band, the gain, the distribution of the surface current, the antenna patterns of the far field and the near field which are given by the HFSS. The frequency characteristics of the input impedance and the gain are also compared in this article.Proceeding from the theory of expanding the band and the feeding problem of the H-shaped planar antenna, the basic theories of the broadband network that are related to the subject is introduced. The discussion in this article focuses on the method of numerical optimization in broadband matching network, which is used to expand the bandwidth when the determined structure of the antenna is analyzed. Moreover, the feeding of the H-shaped antenna is especially studied. Considering that the scattered field existed on the feeding extension line of the H-shaped antenna would affect the parameters of the antenna, this article puts a T-shaped feeding structure designed according to the feeding edge feature and proves that it can meet the needs of the antenna bandwidth theoretically when the equivalent matching network is used. The standing wave and the characteristic of the radiated power of this printed antenna fed by the standard coaxial line are analyzed by the numerical method. The influence on the performance of the antenna produced by this feeding structure is studied quantification ally by the simulation on the computer. Comparing the influence of the standard and T-shaped feeding structures on the standing wave, radiated power and the band of the antenna, we find that the center resonance frequency can be adjusted by changing thelocation of the feeding of the outer conductor. By the simulation of the ANSOFT HFSS, the influence on the bandwidth and the gain affected by the varieties of the length of the outer conductor, the air-gap distance of the antenna and the ground is given out. Furthermore, the graphs of the relations of the structure and the standing wave will give some reference value to the engineering design. Considering the actual size of the feeding notch of the H-shaped antenna, a goal function with constraint conditions is advanced on the basis of the T-shaped feeding in this article. Then it changes into an unrestricted goal function through adding to the penalty function and gets a set of the external diameter values of the coaxial configuration which can match well with the antenna by optimization. According to the chosen values by optimization, the impedance matching device made of two-phase cascade coaxial line is switched into the antenna. The results show that the designed impedance matching device can expend the bandwidth of the antenna.The H-shaped antenna covered by the baton cover is proposed, which can solve the baton problem of the operational force armored cars. Through the simulation and the actual test of the H-shaped antenna covered by the baton cover, the standing wave bandwidth, the radiated power and the gain of the baton antenna are shown. Moreover, using the common whip antenna and the baton antenna carries out the actual test of the communication distance.According to the requirements of the airborne synthetic aperture radar antenna, the major technique of ultra broadband and miniaturized antenna for UHF and the current condition of airborne synthetic aperture radar antenna are analyzed at last. To the problem of its small size, high gain and broadband, the new feeding source of the prismatic plane radar antenna can be used by the two-element antenna array made of the double H-shaped right printed antenna. The radar antenna bandwidth is 2.2 times frequency, and the standing wave inside the band is less then 1.85. Moreover, the gain in the center frequency is more than 9.60dBi and the maximal gain is more than 12dBi. However, its weight is less then 3 kilograms and both the height and the width are less than 1 meter. The electric and non-electric parameters such as the band, the gain and the aerodynamics both meet the design demands. Today, it has already installed on the plane and the test-fly results are satisfying.更多还原