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Characteristic Mode Based Tradeoff Analysis of Antenna-Chassis Interactions for Multiple Antenna Terminals
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
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2012 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 0096-1973, Vol. 60, no 2, 490-502 p.Article in journal (Refereed) Published
Abstract [en]

The design of multiple antennas in compact mobile terminals is a significant challenge, due to both practical and fundamental design tradeoffs. In this paper, fundamental antenna design tradeoffs of multiple antenna terminals are presented in the framework of characteristic mode analysis. In particular, interactions between the antenna elements and the characteristic modes and their impact on design tradeoffs are investigated in both theory and simulations. The results reveal that the characteristic modes play an important role in determining the optimal placement of antennas for low mutual coupling. Moreover, the ability of antenna elements to localize the excitation currents on the chassis can significantly influence the final performance. To demonstrate the effectiveness of the proposed approach, a dual-band, dual-antenna terminal is designed to provide an isolation of over 10 dB for the 900 MHz band without additional matching or decoupling structures. A tradeoff analysis of bandwidth, efficiency, effective diversity gain and capacity is performed over different antenna locations. Finally, three fabricated prototypes verify the simulation results for representative cases.

Place, publisher, year, edition, pages
2012. Vol. 60, no 2, 490-502 p.
Keyword [en]
Antenna array mutual coupling, multiple-input multiple-output (MIMO) systems, mobile communication
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Telecommunications
URN: urn:nbn:se:kth:diva-94066DOI: 10.1109/TAP.2011.2173438ISI: 000302655100008ScopusID: 2-s2.0-84863012797OAI: diva2:525643
QC 20120508Available from: 2012-05-08 Created: 2012-05-07 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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