本文为印度Rourkela国家技术研究所（作者：MANUEL PRASANNA.K）的硕士论文，共82页。

超宽带（UWB）技术在联邦通信委员会（FCC）为UWB应用分配了3.1 - 10.6GHz后，迅速获得了最新无线通信系统的普及和需求。从那时起，超宽带天线系统在高速无线设备中的应用设计就面临着大量的研究机遇和挑战。多输入多输出（MIMO）系统通过部署多个用于传输的天线来实现阵列增益和分集增益，从而在不需要额外带宽或传输功率的情况下显著提高信道容量，进一步提高频谱效率和可靠性。由于MIMO系统采用多副天线，因此需要将天线单元之间进行高度解耦。总的来说，UWB MIMO系统需要小于-16分贝的高隔离度，而且要求尺寸紧凑，能够与集成电路兼容。本论文主要研究在整个UWB（3.1 - 10.6GHz）频段内具有良好工作特性的平面紧凑型多输入多输出（MIMO）天线的分析与设计，以及设计所需要的天线性能。

本文介绍了两单元MIMO天线的设计，以及降低两单元之间相互耦合的各种隔离结构和机制，提出了两种主要的天线设计方案，并分别对隔离度、带宽和辐射特性进行了分析。首先，提出了一种适用于便携式超宽带应用的印刷超宽带MIMO天线系统。MIMO天线系统由两个半圆辐射元件组成，该半圆辐射元件位于一个紧凑尺寸为35 mm×40 mm的低成本FR4基板上，并由一条50Ω微带线馈电。在辐射单元上刻蚀T形槽，以提高阻抗带宽；该天线系统工作在4.4至10.7GHz的宽频范围内。为了提高天线之间的隔离度，在接地面引入了叉型结构。我们获得了该天线系统S参数的仿真结果，并在大部分频带内实现了-20dB的高隔离度，从而证明该设计适用于多输入多输出系统。第二副天线由一个尺寸为36 mm×40 mm的小型平面MIMO天线系统和两个六边形单极子元件组成。六边形缺陷接地结构（DGS）提高了阻抗带宽和隔离性能。仿真结果表明，带DGS的MIMO天线在4.4GHz到9.57GHz之间存在10dB的回波损耗，比不带DGS的传统MIMO天线系统的阻抗带宽提高75%。DGS也提高了隔离性能。S₂₁结果表明，在要求的设计频带内，隔离度超过15分贝，而在大部分频带内，隔离度都超过20分贝。

两个MIMO天线系统的工作带宽几乎覆盖了整个UWB频段，并且与建议的隔离结构一起能够实现超过-16dB的隔离性能。

Ultrawideband (UWB) technology has rapidlygained popularity and demand for recent wireless communication systems afterthe allocation of 3.1- 10.6 GHz by the Federal Communications Commission (FCC)for UWB applications. Since then, a myriad of research opportunities andchallenges exist for the design of UWB antenna systems for application in highspeed wireless devices. Multiple-Input-Multiple-Output (MIMO) systems provide asignificant increase in channel capacity without the need of additionalbandwidth or transmit power by deploying multiple antennas for transmission toachieve an array gain and diversity gain, thereby improving the spectralefficiency and reliability. Since MIMO systems employ multiple antennas, theyrequire high decoupling between antenna elements. Overall UWB MIMO systemsrequire a high isolation of less than -16 dB and also a compact size forcompatibility with integrated circuits. This thesis focuses on the analysis anddesign of MIMO antennas with a compact planar profile that have an operatingrange in the entire UWB (3.1- 10.6 GHz) and desired antenna performancecharacteristics. This dissertation presents the work on the design of two-element MIMO antennas and various isolation structures and mechanisms to reducethe mutual coupling between the two elements, out of which two major antennadesigns are proposed and analyzed separately for their isolation, bandwidth andradiation characteristics. First, a printed ultra wideband (UWB) MIMO antennasystem is proposed for portable UWB applications. The MIMO antenna systemconsists of two semicircular radiating elements on a single low-cost FR4substrate of a compact size of 35 mm× 40 mm and is fed by a50-Ω microstrip line. A T- shaped slot is etched on the radiating elements toenhance the impedance bandwidth. The proposed antenna system operates over awide frequency range from 4.4 to 10.7 GHz . A fork-shaped structure isintroduced in the ground plane to increase the isolation between the antennas.Simulated results of S-parameters of the proposed antenna system are obtainedand a high isolation of -20 dB is achieved in most of the band, which is foundsuitable for MIMO applications. The second antenna consists of a compact planarMIMO antenna system of size 36 mm× 40 mm with twohexagonal monopole elements. The impedance bandwidth and isolation are enhancedby a hexagonal shaped Defected Ground Structure (DGS). Simulated results showthat the MIMO antenna with DGS has 10-dB return loss from 4.4 GHz to 9.57 GHz,yielding 75% improvement in impedance bandwidth over that of the traditionalMIMO antenna system without DGS. Isolation also is enhanced by the DGS. S21results show that isolation exceeds 15 dB within the required band and 20 dB inmost of the band. Both MIMO antenna systems have a significant operatingbandwidth covering almost the entire UWB and together with the proposedisolation structures are able to achieve isolation more than -16 dB.

1 引言

2 微带天线理论

3 UWB MIMO天线系统

4 一种紧凑型的两单元UWB MIMO天线

5 一种带DGS的六边形MIMO天线系统

6 结论与未来工作展望

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