可移动终端的多天线系统研究
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摘要
随着无线通信技术的不断发展,系统对传输速率和可靠性的要求越来越高,多输入多输出(MIMO)系统的研究已经成为近年来非常热门的领域。多输入多输出技术是通过在发射端和接收端引入多天线,在不需要额外的频带和发射功率的情况下,增加系统的信道容量,降低误码率。然而,随着终端设备尺寸的不断缩小,可放置天线的空间非常有限,多天线之间的互相耦合成为多天线系统设计中面临的严峻问题。本论文的目标是针对不同情况下的多天线终端,提出有效的解耦合方案以及单天线的优化技术,为多输入多输出系统提供小型化、低耦合和高性能的多天线设计方案。同时,本论文还提出了一种估算有损天线相关性系数的方法,大大简化了对于多输入多输出天线的测量过程,降低了成本。
本文首先介绍了无线通信领域对于多输入多输出系统的应用需求及其基本原理。其次阐述了多天线系统的相关理论,包括空间复用,分集和波束形成三种应用方式,并详细讨论了影响多天线系统性能的关键因素以及评价多天线系统系能的重要参数,为后续的多天线系统设计提供了基础。为了降低多天线之间的耦合,针对普通地板(ground plane)上的多天线,本文提出了三种不同的解耦合方式,包括缺陷地结构解耦合多天线、电流集中化低耦合多天线、以及极化分集低耦合共位多天线。针对这些解耦合方式,详细介绍其工作机理以及具体天线系统的设计实例和步骤,同时对它们的优缺点以及应用方式进行了比较。这些方法可以有效的应用在大多数终端天线上,至少可以使隔离增强6dB。
在某些特殊情况下,尤其是频带低于1GHz时,终端设备的基板本身也会像天线一样辐射,这使得天线之间的解耦合设计变得异常复杂。为了解决这个问题,本文利用特征模分析法,对基板的辐射模式特征进行了分析。针对分析结果,本文提出了两种不同的解决方案,即优化天线位置分布以及利用磁天线激发正交的辐射模式。这些方法可以广泛地应用在移动电话的LTE700以及GSM1900频段上,极大增强系统的分集性能和信道容量。
要想设计一个高性能、小型化的多天线系统,除了降低天线的耦合,单个天线自身的性能也非常重要。本文针对天线的小型化,提出了一种基于分形结构改进的双频天线。为了弥补小型化天线的带宽缺陷,本文还利用槽天线设计了频率可重构天线,极大的增加了天线的工作带宽。这些单天线结构都可以灵活的应用在多天线系统中,使得多天线系统更加紧凑和有效。
评价一个多天线系统,相关性系数是一个至关重要的参数,然而,利用传统方法测量多天线间的相关性系数时需要三维电场方向图的信息,包括相位信息和极化信息。而这需要特殊的测试设备,测试过程也非常耗时。本论文提出了一种基于等效电路的简化方法,来估算天线间的相关性系数,它可以应用于不同类型的天线,并得到非常可观的精确度。
综上,本论文主要针对小型移动终端的多输入多输出系统,提出了小型化方法,解耦和方法以及相应的测试方法,为移动终端的发展提出了不同的解决方案。
Research on multiple antenna systems has been a hot topic in recent years due to the demands for higher transmission rate and more reliable link in wireless communications. Using multiple antennas at both the transmitter side and the receiver side increases the channel capacity without additional frequency spectrum and transmit power. However, due to the limited space at the size-shrinking terminal devices, the most critical problem in designing multiple antennas is severe mutual coupling. The aim of this thesis is to provide compact, decoupled and efficient multiple antenna designs for terminal devices. At the same time, we propose simple and cost effective method in multiple antenna measurement. All those efforts contribute to the development of terminal devices for the fourth generation wireless communication.
The background and theory of multiple antenna system are introduced first. Critical factors influencing the performance of multiple antennas are discussed, and the parameters to evaluate multiple antenna systems are analyzed in details. To design efficient multiple antenna systems, several decoupling methods, including defected ground plane, current localization and orthogonal polarization, are proposed. The working mechanism and design procedure of each method are introduced, and their effectivenesses are compared. Those methods can be applied to most of the terminal antennas, improving the isolation by6dB at least.
In some special cases, especially at low frequency band below1GHz, the chassis of the device itself radiates like an antenna, which complicates the antenna decoupling. Thus, we extend general decoupling methods to the chassis excited cases. Based on characteristic mode analysis, two different solutions are provided, i.e., optimizing antenna location and creating orthogonal modes by using magnetic antenna. Those methods are applied to mobile phones, providing enhanced diversity and capacity performance.
To design a good multiple antenna system, besides efficient decoupling, the performance of each single antenna is important. A miniaturized single antenna based on fractal structure is then developed. Frequency reconfigurable antenna is also designed, giving more flexibility to multiple antenna systems. All the efforts contribute to compact and efficient multiple antenna terminals.
To measure the performance of a multiple antenna system, it is necessary to obtain the correlation coefficient. However, the traditional measurement technique, which requires the complex values of the electric field, is very expensive and time consuming. In this thesis, a more practical and convenient method is proposed. Fairly good accuracy is achieved when it is applied to various kinds of antennas.
本文首先介绍了无线通信领域对于多输入多输出系统的应用需求及其基本原理。其次阐述了多天线系统的相关理论,包括空间复用,分集和波束形成三种应用方式,并详细讨论了影响多天线系统性能的关键因素以及评价多天线系统系能的重要参数,为后续的多天线系统设计提供了基础。为了降低多天线之间的耦合,针对普通地板(ground plane)上的多天线,本文提出了三种不同的解耦合方式,包括缺陷地结构解耦合多天线、电流集中化低耦合多天线、以及极化分集低耦合共位多天线。针对这些解耦合方式,详细介绍其工作机理以及具体天线系统的设计实例和步骤,同时对它们的优缺点以及应用方式进行了比较。这些方法可以有效的应用在大多数终端天线上,至少可以使隔离增强6dB。
在某些特殊情况下,尤其是频带低于1GHz时,终端设备的基板本身也会像天线一样辐射,这使得天线之间的解耦合设计变得异常复杂。为了解决这个问题,本文利用特征模分析法,对基板的辐射模式特征进行了分析。针对分析结果,本文提出了两种不同的解决方案,即优化天线位置分布以及利用磁天线激发正交的辐射模式。这些方法可以广泛地应用在移动电话的LTE700以及GSM1900频段上,极大增强系统的分集性能和信道容量。
要想设计一个高性能、小型化的多天线系统,除了降低天线的耦合,单个天线自身的性能也非常重要。本文针对天线的小型化,提出了一种基于分形结构改进的双频天线。为了弥补小型化天线的带宽缺陷,本文还利用槽天线设计了频率可重构天线,极大的增加了天线的工作带宽。这些单天线结构都可以灵活的应用在多天线系统中,使得多天线系统更加紧凑和有效。
评价一个多天线系统,相关性系数是一个至关重要的参数,然而,利用传统方法测量多天线间的相关性系数时需要三维电场方向图的信息,包括相位信息和极化信息。而这需要特殊的测试设备,测试过程也非常耗时。本论文提出了一种基于等效电路的简化方法,来估算天线间的相关性系数,它可以应用于不同类型的天线,并得到非常可观的精确度。
综上,本论文主要针对小型移动终端的多输入多输出系统,提出了小型化方法,解耦和方法以及相应的测试方法,为移动终端的发展提出了不同的解决方案。
Research on multiple antenna systems has been a hot topic in recent years due to the demands for higher transmission rate and more reliable link in wireless communications. Using multiple antennas at both the transmitter side and the receiver side increases the channel capacity without additional frequency spectrum and transmit power. However, due to the limited space at the size-shrinking terminal devices, the most critical problem in designing multiple antennas is severe mutual coupling. The aim of this thesis is to provide compact, decoupled and efficient multiple antenna designs for terminal devices. At the same time, we propose simple and cost effective method in multiple antenna measurement. All those efforts contribute to the development of terminal devices for the fourth generation wireless communication.
The background and theory of multiple antenna system are introduced first. Critical factors influencing the performance of multiple antennas are discussed, and the parameters to evaluate multiple antenna systems are analyzed in details. To design efficient multiple antenna systems, several decoupling methods, including defected ground plane, current localization and orthogonal polarization, are proposed. The working mechanism and design procedure of each method are introduced, and their effectivenesses are compared. Those methods can be applied to most of the terminal antennas, improving the isolation by6dB at least.
In some special cases, especially at low frequency band below1GHz, the chassis of the device itself radiates like an antenna, which complicates the antenna decoupling. Thus, we extend general decoupling methods to the chassis excited cases. Based on characteristic mode analysis, two different solutions are provided, i.e., optimizing antenna location and creating orthogonal modes by using magnetic antenna. Those methods are applied to mobile phones, providing enhanced diversity and capacity performance.
To design a good multiple antenna system, besides efficient decoupling, the performance of each single antenna is important. A miniaturized single antenna based on fractal structure is then developed. Frequency reconfigurable antenna is also designed, giving more flexibility to multiple antenna systems. All the efforts contribute to compact and efficient multiple antenna terminals.
To measure the performance of a multiple antenna system, it is necessary to obtain the correlation coefficient. However, the traditional measurement technique, which requires the complex values of the electric field, is very expensive and time consuming. In this thesis, a more practical and convenient method is proposed. Fairly good accuracy is achieved when it is applied to various kinds of antennas.
引文
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