【作者】 马汉清；

【导师】 褚庆昕；

【作者基本信息】 西安电子科技大学 ， 电磁场与微波技术， 2009， 博士

【摘要】 目前的通信系统一直在向宽带化、集成化发展,同时人们对便携移动通信的需求也越来越高,这要求天线发展出与之相适应的宽带技术、多频技术与小型化技术。论文紧贴目前一些通信系统的需求,围绕VHF/UHF一体化小型天线、板载移动终端天线和宽方向图带宽天线等几个问题展开了研究,主要工作和取得的成果如下:1有限地面上电小天线相关理论的研究。介绍了电小天线的尺寸与Q值和带宽之间的关系,着重研究了金属半球上和金属圆盘上天线Q值的理论极限问题,首次提出了求解这两种情况下电小天线Q值的下限的方法,且发现其Q值极限随地面半径按近似贝塞尔函数的规律变化。根据上述结论,提出了一个猜想:对旋转对称导体上的半径为a的封闭半球内的垂直极化全向电小天线来说,获得最小Q值时,半球外的场应与同样导体上单极子的场一致。2天线最优化算法的研究。回顾了最优化算法在天线设计领域中的应用,分析了各种算法的特点。考虑到天线设计问题的特点,将粒子群算法与单纯形法相结合,提出了淘金粒子群算法,使用测试函数验证了算法效果。给出了优化算法调用CST软件作为解算器的方法,从而使电磁场仿真软件与最优化技术可以无缝结合,大大提高了天线设计效率。作为应用实例,用此算法设计了串联馈电的波束赋形天线,提出了使用阶梯阻抗线对微带缝隙和同轴缝隙串联馈电以实现赋形波束设计的方法。所设计的900MHz同轴缝隙天线,可以实现H面全向,E面赋形波束设计,适用于基站天线;另一实例为3.5GHz微带缝隙天线,可实现双侧赋形波束,适用于高速公路、隧道等狭长地形的信号覆盖。实验验证了微带缝隙天线的性能,结果表明天线垂直放置时可在95-135度仰角范围内实现近平方余割波束,同时将上半空间副瓣电平抑制在-19dB以下。3 VHF/UHF一体化小型天线的研究。研究了两种电小尺寸下一体化天线设计方案,并制作了实验样机。其中一种天线为42cm×20cm的平面结构,在30-86MHz频段及110-600MHz频段VSWR＜3,在频率低端增益大于-22dB,频率高端增益大于-5dB,此外还实现了86-110MHz频率的带外阻塞特性,同时考虑了与另一L波段天线共口径设计的问题;而另外一种集总元件加载多臂折叠天线的设计理念来自于天线Q值理论,通过多臂折叠结构和臂间加载实现了天线安装空间的高效利用,并实现了比较理想的辐射效率与阻抗带宽的折衷。分析了两种天线的性能极限,并讨论了接地板大小对宽带天线辐射效率的影响,对实际电小天线设计有很好的指导作用。4移动终端板载宽带与多频天线的研究。设计了一种用于数字电视接收终端的小型化板载天线,一种用于WLAN的板载双频天线和一种WLAN/WiMAX频率使用的三频天线,讨论了载体板对天线性能的影响,研究了减少天线性能对载体板依赖性的几种技术手段,提出了小型化与宽带载体板扼流结构,并在此基础上设计了一种受载体板影响小的双频天线。给出了上述几种天线的仿真与实测结果。5方向图带宽有特殊要求天线的研究。研究了一种E面全向宽带天线,使用改进的4元T型印刷振子阵列,通过引入了振子间耦合结构,改善天线上电流分布,获得了宽带E面全向特性;还研究了一种应用于WLAN或ISM频率的宽带高增益天线,通过在常规的浅背腔微带缝隙天线上覆盖一开窗金属板,实现了天线增益的提高与阻抗带宽的展宽,其最大增益可达12.3dB,研究了这种天线的工作机理,并给出了设计准则和初始参数选取办法。更多还原

【Abstract】 With the rapid development of wide band communication system and the increasing requirements on portable mobile communications, compact and multifunctional wireless communication systems have spurred the development of multi-band and wideband antennas with small size. With focus on those new demands, this dissertation is mainly concerned with the VHF/UHF dual-wideband compact antennas, mobile terminal antennas built on planar system ground plane and some antennas with wide radiation pattern bandwidth. The author’s major contributions are outlined as follows:1、The basic principle on electronically small antennas over finite ground is investigated. Begins with the relation between size, Q value and bandwidth of electrically small antenna, the lower bounds of the radiation Q for electrically small antennas above conductive hemispheres and flat disks are first calculated. It is found that the Q limitation variations with the radius of ground plane according to the Bessel functions. A conjecture is proposed: For an antenna enclosed in a hemisphere over a rotational symmetric conductor, when the lowest Q amplitude is achieved, its field outside the hemisphere should correspond to that of an infinitesimally small dipole.2、Optimization methods for antenna design are investigated. After a quick review on some well known optimization design methods for antenna design, a modified Particle Swarm Optimization (PSO), named as Gold Rush PSO is proposed by combining PSO with standard Simplex method. Its performance is verified by several benchmark functions. The combination of optimization methods and the CST software is also considered, where the CST works as a subprogram that can do a full-wave analysis and return results to the main program. As examples, both a multiple circumferential slotted coaxial antenna and a microstrip slot array are designed using this method to achieve shaped radiation pattern. The shaped beam is realized by adjusting the feed line that composed of stepped impedance lines. The slotted coaxial antenna operating at 900 MHz radiates omnidirectional in its H plane, while has a shaped beam in its E plane, which makes it a good candidate for base station antenna. The microstrip slot array antenna has dual-side shaped beam with elevation coverage of 35°, a gain of 10.86dBi and side lobe levels less than -19dB, which make it suit for used in a narrow and long zone such as highways or tunnels. Experimental results demonstrate the validity of this design.3、VHF/UHF dual-wideband compact antennas are studied. Two very compact wideband antennas are designed and prototypes are fabricated and measured. One antenna is planar and has a compact size of only 42cm×20cm, while it covers 30-86 MHz and 110-600MHz with VSWR <3 and band notched in 86-110 MHz. This antenna has gain values larger than -21dBi in the lower frequency band and larger than -5 dBi in the upper band, respectively. Besides, the design of sharing aperture with an L band antenna is also considered. The design idea of the other antenna that has multiple-arm folded wire structure comes from the Q value theory, which makes the antenna has a high utilization efficiency of antenna mounting room. A reasonable tradeoff between radiation efficiency and VSWR bandwidth is achieved by folded multiple-arm structure and lumped elements loaded between arms. In addition, the theoretical performance limits of the two antennas and the influence of ground plane size on the antenna bandwidth are both analyzed, which give decisive guidance to electronically small antenna design.4、Wide band and dual band onboard antennas are investigated. A compact wideband antenna for digital television (DTV), a dual band antenna for WLAN and a tri-band antenna for WLAN/WiMax are proposed. The influence of system ground board on antenna performance is discussed. Methods to mitigate the strong dependence of impedance bandwidth on the ground plane size for onboard antenna are investigated; a novel compact current chocker and a wide band chocker are proposed. Based on those techniques, a ground plane independent dual band antenna is proposed. Measured results of the aforementioned antennas are given.5、Two Antennas with wide radiation pattern bandwidth are designed. A wideband antenna that has omnidirectional radiation in its E plane is proposed. It consists of four modified T-dipoles, with the coupling structure between dipoles the current distribution on the antenna is improved to radiate in omnidirectional E patterns. A novel low profile high gain cavity backed and metallic superstrate covered slot antenna that operates in the 2.4GHz WLAN or ISM band is described. The proposed antenna has a bandwidth of 12% and a gain of 12.3dBi at its center frequency. Moreover, its radiation mechanism is investigated and the design guidelines of this kind of antenna are given.更多还原