【作者】 刘震；

【导师】 杨峰；

【作者基本信息】 电子科技大学 ， 电磁场与微波技术， 2019， 硕士

【摘要】 相控阵技术可用于控制天线阵列的波束指向,相比传统的机械扫描方式,阵列波束的扫描速度更快,精度更高。随着相控阵技术在目标搜索、识别、跟踪等方面的广泛应用及发展,具有宽角、低副瓣扫描特性的相控阵天线成为天线领域研究的焦点。为了实现相控阵天线的宽角、低副瓣扫描特性,本文把人工电磁材料应用到天线的设计中,研究并分析了加载人工电磁材料的天线单元特性及阵列的扫描特性。移相器是相控阵天线中的重要器件。移相器的特性会影响相控阵的性能。传统的基于铁氧体、变容二极管及开关型移相器,存在体积大、响应速度慢、功耗大、插入损耗大、成本高等问题。而液晶材料在高频段(大于10GHz)的物理特性稳定,损耗小,且液晶的介电常数在偏置电压的作用下可发生变化。基于液晶材料的移相器,由于具有结构设计简便、损耗小、相位可连续调节、成本低等优势,成为近年来研究的热点。基于以上研究背景,本文把一种蘑菇型结构的负介电常数传输线(Epsilon Negative Transmission Line,ENG TL)单元用于天线的设计中,来降低互耦;还将一种支持表面波传播的高阻抗表面结构用在天线的设计中,以展宽天线的波束宽度,实现相控阵天线波束的宽角扫描。为了实现相控阵天线的电扫描特性,把液晶材料用在移相器的设计中。具体工作总结如下:第一、基于ENG TL结构的天线设计。ENG TL结构用在天线单元的设计中,可以有效降低阵列环境中天线间的互耦,减小天线的后向辐射。但是加载ENG TL结构,会使天线单元的尺寸增大,在阵列环境中不得不增大阵元间距,导致阵列出现栅瓣。而本文通过在天线及ENG TL结构中合理开槽,实现了天线单元的小型化,将其应用于相控阵中,增大了阵列的扫描范围,再结合阵列综合算法降低了阵列扫描过程中的副瓣电平。最后通过在中心辐射贴片开槽,产生两个相位差90°的简并模分离单元,实现了天线单元的圆极化辐射。第二、基于高阻抗表面的天线设计。以经典的蘑菇型结构为基础,设计了矩形结构的蘑菇型单元,并通过开缝实现了结构单元的小型化,分析了单元结构参数对频率带隙特性的影响。在带隙频段外,根据这种结构支持表面波传播的特性,设计了宽波束天线单元并组成阵列,通过控制每个阵元的馈电相位,实现了阵列的宽角扫描。第三、基于液晶材料的移相器设计。基于液晶材料的介电各向异性,在传统微带线移相器结构的基础上,把液晶材料作为微带线的填充介质,设计了一种相移量可调的微带线移相器。分析了影响微带线移相器性能的各种结构参数,最终设计的微带线移相器具有较大相移量,低插入损耗,小型化的特性。在需要较大相移量的情况下,微带线移相器的尺寸会增大。而反射型移相器,通过合理设计反射负载的结构,可以降低移相器的尺寸。传统的加载开关元件或变容二极管电抗网络的反射型移相器,工作频率升高时,插入损耗增大。而以液晶材料为介质的负载电抗随着液晶介电常数的变化而改变,并且工作频率升高时,液晶的物理特性保持稳定,损耗也更低,取代传统的变容二极管或开关元件,可以有效提高移相器的性能。更多还原

【Abstract】 Phased array technology can control the beam pointing of antenna array.Compared with traditional mechanical scanning mode,the beam scanning speed of antenna is faster and the precision is higher.With the wide application and development of phased array technology in target search,recognition and tracking,the phased array antenna with wide angle and low side lobe scanning characteristics has become the focus of research in the field of antenna.In order to realize the wide angle and low side lobe scanning characteristics of phased array antenna,artificial electromagnetic materials are applied to the design of antenna structure.The characteristics of antenna elements and arrays loaded with artificial electromagnetic materials are studied and analyzed.Phase shifter is the key component of phased array antenna,its characteristics will affect the performance of the whole phased array.Traditional phase shifter based on ferrite,varactor and switch have many problems,such as large volume,slow response speed,high power consumption,high insertion loss and high cost.However,the physical properties of liquid crystal materials at high frequencies(greater than 10GHz)are stable and the loss is small,and the dielectric constant of liquid crystal can change under the action of bias voltage.The phase shifter based on liquid crystal materials has become a research hotspot in recent years due to its advantages of simple structure design,low loss,continuous phase adjustment and low cost.Based on the above research background,a mushroom-type Epsilon Negative Transmission Line(ENG TL)element is used in the design of antenna elements to reduce mutual coupling,and a high impedance surface element supporting surface wave propagation is used in the antenna structure to expand the beam width of the antenna and realize wide-angle scanning of the phased array antenna beam.In order to realize the scanning characteristics of phased array,liquid crystal material is used in the design of phase shifter.The main research contents of the dissertation are summarized as follows:First,antenna design based on ENG TL structure.The ENG TL structure used in the design of antenna elements can effectively reduce the mutual coupling in the array environment and the backward radiation of the antenna.However,the size of the antenna element increases with the loading of ENGTL structure,and the spacing of the elements has to be increased in the array environment,resulting in the occurrence of grating lobes in the array.In this paper,the antenna element is miniaturized by reasonable slots in the antenna and ENG TL structure.It is applied to phased array,which enlarges the scanning range of the array.Combined with the array optimization algorithm,the side lobe level in the scanning process of the array is reduced.Finally,by slotting the central radiation patch,two degenerate mode separation elements with 90 degree phase difference are generated,and the circular polarization radiation of the antenna element is realized.Second,antenna design based on high impedance surface.Based on the classical mushroom-type structure,a rectangular mushroom-type element is designed,and the structure element is miniaturized by slitting.The influence of the structural parameters of the element on the band gap characteristics is analyzed.In addition to the band gap,according to the characteristics of the structure supporting surface wave propagation,a wide-beam antenna element is designed and an array is formed.By controlling the feed phase of each element,the wide-angle scanning of the array is realized.Thirdly,phase shifter design based on liquid crystal materials.Based on the dielectric anisotropy of liquid crystal material and the traditional microstrip line phase shifter structure,a microstrip line phase shifter with adjustable phase shift is designed by using liquid crystal material as the filling medium of microstrip line.Various structural factors affecting the performance of microstrip phase shifter are analyzed.The final design of microstrip phase shifter has the characteristics of large phase shift,low insertion loss and miniaturization.The size of microstrip line phase shifter will increase when a larger phase shift is needed.The size of the phase shifter can be reduced by reasonably designing the structure of the reflection load.Traditional reflective phase shifters loaded with switching elements or varactor reactance networks increase insertion loss when operating frequency increases.The load reactance of liquid crystal material changes with the change of dielectric constant of liquid crystal.When the working frequency increases,the physical characteristics of liquid crystal remain stable and the loss is lower.The performance of phase shifter can be effectively improved by replacing the traditional varactor diode or switching element.更多还原