多极化MIMO天线设计理论及性能研究

Multipolarized antenna or vector antenna can make full use of the vector nature of electromagnetic (EM) field, which has great potential in the dense antenna array MIMO communications and the high-resolution radar systems. Theoretical researches indicate that, in a rich scattering environment, the maximum MIMO channel capacity gain obtained from the hexa-polarized (HP) antenna can reach almost 6 times of that obtained from the uni-polarized system. However, at present, the realized vector antenna having the maximum polarizations is a quad-polarized one. Thus, the systematic and thorough research about the characteristics of the HP MIMO channel cannot be conducted by field experiments, the clear understanding about the inherent relationship between the scattering mechanism and the coupling effect among polarizations are not obtained. The purpose of this research is to design a colocated orthogonal and low coupled HP MIMO antenna working at sub 6 GHz and the multipolarized MIMO antenna arrays working at millimeter wave frequency band with high-gain, low coupling and low correlation. We plan to get multiple orthogonal polarization modes from a single radiation object by multiple feedings, and also use the electromagnetic band gap (EBG) material to reduce the mutual couplings among multiple modes. Based on the designed antennas, some channel propagation measurement experiments in several typical indoor and outdoor wireless applications will be conducted, through which the accuracy of the channel modeling theory can be verified and some advancements and modifications will be made from the former channel modeling theory of multipolarized MIMO system. This project will discover the ultimate potential of the information transferring capability obtained by making full use of the vector nature of EM field, and provide theoretical guidance for the realization of multipolarized MIMO antenna element and antenna array in the future cellular and wireless LAN networks.

多极化天线能更充分利用电磁场的矢量特性，在密集天线阵MIMO通信和高分辨率雷达等系统都有重要应用前景。理论研究表明在散射丰富信道中，6极化MIMO系统信道容量最大可接近单极化系统的6倍，但已实现维数最多的是四极化天线，因此无法通过实验对6极化MIMO信道特性进行系统深入的研究，对环境散射机理与极化耦合间的内在关系也缺乏透彻的理解。本项目目标是获得6GHz以下频段共点正交低耦合6极化天线和毫米波段高增益、低耦合、低相关性的多极化MIMO天线阵。准备利用对单个辐射体进行多种激励来获得多个极化模式，并结合EBG材料来降低耦合，利用所设计天线对一些典型室内外无线应用的信道特性进行测量，并与信道建模理论结果相互验证，完善现有多极化MIMO信道建模理论。本项目将从实验方面揭示充分利用电磁场的极化状态来获得信息传输能力提升的极限，为未来蜂窝网和无线局域网等系统中多极化MIMO天线的实现提供理论指导。

共点正交的多极化天线可以使电磁场的矢量特性被更充分地利用，因此在高容量MIMO通信和高分辨率MIMO雷达等系统中都具有重要的应用前景，然而，实现紧凑型、共点正交、低耦合的多极化天线始终是国际天线设计领域的难题，严重制约了多极化技术的应用与发展。.本项目针对上述问题，在多极化MIMO天线设计理论与实现和信道特性研究等方面开展了一些前瞻性和探索性的研究，并取得了一批具有原创性和突破性的学术成果。（1）提出了基于模式复用理论的多极化天线设计理论架构，由单个辐射体在不同位置激励出不同的模式来获得多个极化，实现了一种基于平面微带结构的三极化天线，并在此基础上提出了一种基于过孔加载寄生贴片的天线小型化技术，可使其在厚度不增加的前提下尺寸由0.7λ降至0.485λ，并使端口间的最大耦合从-13dB降为-18dB，给出了其工作原理的等效传输线模型解释；（2）提出了三种共点正交、低耦合的四极化天线，第一种由二个正交的双模环天线构成，耦合约-15dB，第二种基于二个正交的环天线和二个正交的电偶极子天线，通过添加电磁带隙结构使耦合降为-30dB，第三种为平面结构，由一个双模环天线和一个双极化微带天线构成，耦合低于-15dB；（3）提出了一种基于谐振腔的毫米波多极化MIMO天线，可充分利用单个谐振腔使多个具有不同极化的激励天线同时实现增益的提高；（4）基于以上几种多极化天线，在一些具有不同多径分布的直射和非直射环境中，进行了大量的信道测量，并对其MIMO信道参数进行了提取、分析和研究，发现三极化和四极化MIMO天线在散射信道中可以分别获得三个和四个独立的并行子信道；（5）提出了一种宽角度三极化回溯阵，通过接收和辐射三个正交极化分量的电磁波，使其对任意极化方向的来波进行回溯并通过方向图互补来扩宽回溯角度范围。.以上研究成果为多极化MIMO天线的设计、实现及应用提供了重要的解决方案。