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Decoupling of Multiple Antennas in Terminals With Chassis Excitation Using Polarization Diversity, Angle Diversity and Current Control
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.ORCID iD: 0000-0002-3401-1125
2012 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 0096-1973, Vol. 60, no 12, 5947-5957 p.Article in journal (Refereed) Published
Abstract [en]

Excitation of the chassis enables single-antenna terminals to achieve good bandwidth and radiation performance, due to the entire chassis being utilized as the main radiator. In contrast, the same chassis excitation phenomenon complicates the design of multiple antennas for MIMO applications, since the same characteristic mode of the chassis may be effectively excited by more than one antenna, leading to strong mutual coupling and severe MIMO performance degradation. In this paper, we introduce a design concept for MIMO antennas to mitigate the chassis-induced mutual coupling, which is especially relevant for frequency bands below 1 GHz. We illustrate the design concept on a dual-antenna terminal at 0.93 GHz, where a folded monopole at one chassis edge excites the chassis' fundamental electric dipolemode and a coupled loop at the other chassis edge excites its own fundamental magnetic dipole mode. Since the two radiationmodes are nearly orthogonal to each other, an isolation of over 30 dB is achieved. Moreover, we show that the antenna system can be conveniently modified for multiband operation, such as in the 900/1800/2600MHz bands. Furthermore, by controlling the phase of the feed current on the folded monopole, the two antennas can be co-located on the same chassis edge with an isolation of over 20 dB. The co-located dual-antenna prototype was fabricated and verified in the measurements.

Place, publisher, year, edition, pages
2012. Vol. 60, no 12, 5947-5957 p.
Keyword [en]
Antenna array, mutual coupling, MIMO systems, mobile communication
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Telecommunications
URN: urn:nbn:se:kth:diva-96243DOI: 10.1109/TAP.2012.2213056ISI: 000312032800045ScopusID: 2-s2.0-84870894280OAI: diva2:529817
Vinnova, 2009-02969Swedish Research Council, 2010-468

QC 20130108. Updated from accepted to published.

Available from: 2012-05-31 Created: 2012-05-31 Last updated: 2013-11-19Bibliographically approved
In thesis
1. Decoupling and Evaluation of Multiple Antenna Systems in Compact MIMO Terminals
Open this publication in new window or tab >>Decoupling and Evaluation of Multiple Antenna Systems in Compact MIMO Terminals
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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 rich scattering environment in wireless communications. Using multiple antennas at both the transmitter side and the receiver side increases the channel capacity without additional frequency spectrum and transmitted power. However, due to the limited space at the size-limited terminal devices, the most critical problem in designing multiple antennas is the severe mutual coupling among them. The aim of this thesis is to provide compact, decoupled and efficient multiple antenna designs for terminal devices. At the same time, we propose a simple and cost effective method in multiple antenna measurement. All these efforts contribute to the development of terminal devices for the fourth generation wireless communication.

The background and theory of multiple antenna systems are introduced first, in which three operating schemes of multiple antenna systems are discussed. Critical factors influencing the performance of multiple antenna systems are also analyzed in details. To design efficient multiple antenna systems in compact terminals, several decoupling methods, including defected ground plane, current localization, orthogonal polarization and decoupling networks, are proposed. The working mechanism and design procedure of each method are introduced, and their effectiveness is compared. Those methods can be applied to most of the terminal antennas, reducing the mutual coupling by at least 6dB.

In some special cases, especially for low frequency bands below 1GHz, the chassis of the device itself radiates like an antenna, which complicates the antenna decoupling. Thus, we extend the general decoupling methods to the cases when the chassis is excited. Based on the characteristic mode analysis, three different solutions are provided, i.e., optimizing antenna locations, localizing antenna currents and creating orthogonal modes. These methods are applied to mobile phones, providing a more reliable link and a higher transmission rate, which are evaluated by diversity gain and channel capacity, respectively.

In order to measure the performance of multiple antenna systems, it is necessary to obtain the correlation coefficients. However, the traditional measurement technique, which requires the phase and polarization information of the radiation patterns, 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.

To design a compact and efficient multiple antenna system, besides the reduction of mutual coupling, the performance of each single antenna is also important. The techniques for antenna reconfiguration are demonstrated. Frequency and pattern reconfigurable antennas are constructed, providing more flexibility to multiple antenna systems.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xvi, 89 p.
Trita-EE, ISSN 1653-5146 ; 2012:025
Multiple antennas, mutual coupling, compact antennas, frequency reconfigurable antennas, pattern reconfigurable antennas, meta-material antennas, mobile antennas, fractal antennas, collocated antennas, antenna measurement.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
urn:nbn:se:kth:diva-96239 (URN)
Public defence
2012-06-15, H1, Teknikringen 33, KTH, Stockholm, 10:00 (English)
QC 20120604Available from: 2012-06-04 Created: 2012-05-31 Last updated: 2012-06-04Bibliographically approved

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