【作者】 李学识；

【导师】 胡斌杰；

【作者基本信息】 华南理工大学 ， 电磁场与微波技术， 2010， 博士

【摘要】 现代移动通信系统的高速发展对通信系统前端的天线提出了更高的要求。通信天线正在向着频率可重构和方向图可重构的方向发展。相比传统金属天线,等离子体天线具有其独特的优点:通过控制等离子体参数,可以使天线的输入阻抗、辐射方向图、效率和工作带宽等特性实现动态重构;其次,等离子体天线在没有激发的时候是普通介质,雷达散射截面极小,因此它在军事及民用领域具有重要的战略意义。本文首先分析了表面波驱动等离子体天线的辐射原理,建立了非磁化等离子体天线分析的DI-FDTD(Direct Integration Finite-Difference Time-Domain,直接积分FDTD)数值模型和磁化等离子体天线分析的PLRC-FDTD(Piecewise Linear Recursive Convolution FDTD,分段线性卷积FDTD)模型。在此基础上,探讨了等离子体参数对天线近场与远场特性的影响,以及等离子体天线阵列的方向图可重构性。论文的主要工作和创新点如下:(1)非磁化等离子体天线辐射性能研究和优化设计。针对实际天线应用的需要,建立了容性激励馈电的介质管圆柱状等离子体天线模型。采用DI-FDTD算法对非磁化等离子体天线的远场辐射方向图和天线效率等性能指标进行了分析。仿真结果表明:介质管的介电常数对于天线的远场辐射强度和效率有比较明显的作用,设计实际天线时可以通过设置恰当的介质管介电常数完成对等离子体天线的辐射性能的优化。(2)磁化等离子体天线辐射特性研究与动态控制技术。采用PLRC-FDTD算法对磁化等离子体天线的输入阻抗、远场辐射方向图、天线效率等性能指标进行模拟分析。仿真结果表明:外磁场的强弱变化对天线的输入阻抗与辐射功率有比较明显的作用,因此可以利用外磁场实现磁化等离子体天线工作带宽和辐射强度的动态控制。(3)磁化等离子体天线具有非均匀等离子体分布时的数值建模与分析。针对等离子体天线激发之后介质管中的等离子体密度可能具有非均匀分布的实际情况,建立了轴向和径向非均匀分布的磁化等离子体天线模型。采用PLRC-FDTD算法对其影响进行了仿真分析,仿真结果表明:等离子体的非均匀分布使磁化等离子体天线的输入阻抗略向低频移动,而辐射强度略有降低。但是在轴向和径向非均匀分布分别为15%和10%的情况下,非均匀分布的磁化等离子体天线的效率仍然达到76%。(4)等离子体天线阵列辐射特性研究及方向图动态可重构设计。建立了等离子体天线阵列的DI-FDTD数值模型,并对等离子体天线多元阵列的辐射性能进行仿真分析。仿真结果表明:等离子体天线阵列中一个天线单元的等离子体参数变化,可以使整个天线阵列的辐射方向图的强度和指向性发生较明显的变化。在此基础上设计了四阵元、六阵元和八阵元的等离子体天线阵列,以实现方向图的动态可重构特性。更多还原

【Abstract】 The rapid development of modern mobile communication systems set higher demands toward antennas in front of communication systems. Communication antennas are developing towards the trend of frequency reconfiguration and pattern reconfiguration. Compared with traditional metal antennas, plasma antennas have their special characteristics: Firstly, by controlling the parameters of the plasma, the input impedance, radiation pattern, antenna efficiency and bandwidth of the plasma antenna can be dynamically reconfigured. Secondly, the plasma antenna would turn into a normal dielectric material without excitation, letting its radar cross section negligible. Thus plasma antennas have strategic significance in the military and civil field.The thesis theoretically analyses the radiation mechanism of the surface driven plasma antenna. The numerical model of DI-FDTD (Direct Integration Finite-Difference Time-Domain) method is constructed for the unmagnetized plasma antenna and the model of PLRC-FDTD (Piecewise Linear Recursive Convolution FDTD) method is constructed for the magnetized plasma antenna. On the basis of these models, the influences of plasma parameters on the antenna’s near and far field characteristics and the pattern reconfigurability of the antenna is discussed. The main work and creative points of the thesis are as follows:(1) Research on the radiation performance of the unmagnetized plasma antenna and optimization of its performance. Considering requirements in real applications of antennas, a model of a cylindrical plasma antenna encapsulated in a dielectric tube and excited by a capacitively coupling sleeve is built. The DI-FDTD algorithm is utilized to perform simulation on the far-field radiation pattern and the antenna efficiency of the unmagnetized plasma antenna. Simulation results show that the permittivity of the dielectric tube have obvious effects on the far-field radiation pattern and efficiency of the antenna. Thus the radiation performance of a plasma antenna can be optimized by properly setting the permittivity of the dielectric tube.(2) Research on the radiation performance of the magnetized plasma antenna and the technology of dynamically tuning its performance. The PLRC-FDTD method is employed to numerically analysis the input impedance, radiation pattern and antenna efficiency of the magnetized plasma antenna. Numerical results show that the variation of the external magnetic fields have obvious effects on the performance of the antenna. Thus the external magnetic field can be used to dynamically control the bandwidth and radiation pattern of the magnetized plasma antenna.(3) Investigation on the performance of the magnetized plasma antenna with a non-uniform plasma distribution. Considering the situation that the plasma excited in a dielectric tube may be non-uniformly distributed, the model of a both axially and radically non-uniformly distributed magnetized plasma antenna is designed. By using the PLRC-FDTD method, its influence is numerically analyzed. Simulation results show that the non-uniform plasma distribution leads the input impedance of the antenna to shift slightly toward lower frequency and causes the radiation efficiency to fall a bit. However, the magnetized plasma antenna with 15% axial-nonuniform and 10% radial-nonuniform distribution has still achieved 76% radiation efficiency.(4) Research on the radiation performance of the plasma antenna array and design of the pattern reconfiguration. The DI?FDTD numerical model of the plasma antenna array is constructed and utilized to simulation its radiation performance. Simulation results show that the change of plasma parameters of one antenna in the array will draw obvious influences on the radiation pattern and direction of the array. On this basis, the plasma antenna arrays of four elements, six elements and eight elements are designed to realize the dynamic reconfigurability of the radiation pattern.更多还原