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Decoupling and Evaluation of Multiple Antenna Systems in Compact MIMO Terminals
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
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.
Series
Trita-EE, ISSN 1653-5146 ; 2012:025
Keyword [en]
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
Identifiers
URN: urn:nbn:se:kth:diva-96239OAI: oai:DiVA.org:kth-96239DiVA: diva2:529797
Public defence
2012-06-15, H1, Teknikringen 33, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120604Available from: 2012-06-04 Created: 2012-05-31 Last updated: 2012-06-04Bibliographically approved
List of papers
1. A Compact Planar MIMO Antenna System of Four Elements With Similar Radiation Characteristics and Isolation Structure
Open this publication in new window or tab >>A Compact Planar MIMO Antenna System of Four Elements With Similar Radiation Characteristics and Isolation Structure
2009 (English)In: IEEE Antennas and Wireless Propagation Letters, ISSN 1536-1225, E-ISSN 1548-5757, Vol. 8, 1107-1110 p.Article in journal (Refereed) Published
Abstract [en]

A compact planar multiple-input-multiple-output (MIMO) antenna system of four elements with similar radiation characteristics is proposed for the whole 2.4-GHz WLAN band. It consists of two proximity-coupled fed microstrip square ring patch antennas and two lambda/4 microstrip slot antennas of the same linear polarization. These two types of antennas are printed on different sides of the substrate to reduce mutual coupling. With a novel isolation structure etched on the ground plane of the FR4 substrate, high port isolation (below -25 dB) and good MIMO performance are achieved. The overall lateral size of the MIMO system is only 0.64 lambda X 0.48 lambda, and good impedance matching (S11 < 10 dB) is achieved across the operating band for all the antenna elements. Full spherical radiation patterns are measured for the MIMO system, showing similar radiation characteristics, and the gains are above 2.3 dB across the operating band.

Keyword
Compact antenna, isolation technology, multiple-input-multiple-output, (MIMO) systems, wireless LAN
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-18932 (URN)10.1109/lawp.2009.2034110 (DOI)000271440900003 ()
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Extremely compact dual-band PIFAs for MIMO application
Open this publication in new window or tab >>Extremely compact dual-band PIFAs for MIMO application
2009 (English)In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 45, no 17, 869-U20 p.Article in journal (Refereed) Published
Abstract [en]

A MIMO structure consisting of two extremely compact planar inverted-F antennas (PIFAs) (lambda/60 x lambda/20 x lambda/6) is proposed for GSM 900 MHz and 2.4 GHz wireless local area network applications. The miniaturisation of each antenna is achieved through a spiral-shaped PIFA and a capacitive load, forming a LC resonator. Both antennas have a good impedance bandwidth of 0.88-0.945 and 2.39-2.48 GHz for 0.9 and 2.4 GHz band, respectively. The two PIFA antennas are polarised orthogonally to each other, and isolation better than 228 dB is achieved in both bands without any structure etched on the ground. The predicted results are compared with the measured data and good agreement is found.

Keyword
antenna
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-18700 (URN)10.1049/el.2009.1336 (DOI)000269196400006 ()
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
3. Compact and low profile co-located MIMO antenna structure with polarisation diversity and high port isolation
Open this publication in new window or tab >>Compact and low profile co-located MIMO antenna structure with polarisation diversity and high port isolation
2010 (English)In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 46, no 2, 108-109 p.Article in journal (Refereed) Published
Abstract [en]

A compact co-located MIMO structure with high port isolation is proposed for 2.4 GHz WLAN application. The antenna structure consists of a proximity-coupled square ring patch antenna, and a probe fed planar inverted F antenna co-located inside. The operating frequency of the two radiators is designed to be at the same frequency, and a high port isolation below -25 dB is achieved with an extremely narrow edge to edge inter-antenna space of 1 mm (0.008 lambda). The total lateral size of the co-located radiators is only 0.28 lambda x 0.28 lambda, i.e. only about 25% of the size of a half-wavelength dual-port patch antenna. The MIMO structure gives high gains (> 4.0 dB), low correlation (< 0.2), and high diversity gain (about 10 dB).

Keyword
wireless channel
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-19133 (URN)10.1049/el.2010.2463 (DOI)000273889600005 ()2-s2.0-77949986008 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
4. Characteristic Mode Based Tradeoff Analysis of Antenna-Chassis Interactions for Multiple Antenna Terminals
Open this publication in new window or tab >>Characteristic Mode Based Tradeoff Analysis of Antenna-Chassis Interactions for Multiple Antenna Terminals
Show others...
2012 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, 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.

Keyword
Antenna array mutual coupling, multiple-input multiple-output (MIMO) systems, mobile communication
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Telecommunications
Identifiers
urn:nbn:se:kth:diva-94066 (URN)10.1109/TAP.2011.2173438 (DOI)000302655100008 ()2-s2.0-84863012797 (Scopus ID)
Note
QC 20120508Available from: 2012-05-08 Created: 2012-05-07 Last updated: 2017-12-07Bibliographically approved
5. Decoupling of Multiple Antennas in Terminals With Chassis Excitation Using Polarization Diversity, Angle Diversity and Current Control
Open this publication in new window or tab >>Decoupling of Multiple Antennas in Terminals With Chassis Excitation Using Polarization Diversity, Angle Diversity and Current Control
2012 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, 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.

Keyword
Antenna array, mutual coupling, MIMO systems, mobile communication
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Telecommunications
Identifiers
urn:nbn:se:kth:diva-96243 (URN)10.1109/TAP.2012.2213056 (DOI)000312032800045 ()2-s2.0-84870894280 (Scopus ID)
Funder
Vinnova, 2009-02969Swedish Research Council, 2010-468
Note

QC 20130108. Updated from accepted to published.

Available from: 2012-05-31 Created: 2012-05-31 Last updated: 2017-12-07Bibliographically approved
6. Isolation enhancement of compact MIMO antennas with current localization
Open this publication in new window or tab >>Isolation enhancement of compact MIMO antennas with current localization
Show others...
(English)Article in journal (Other academic) Submitted
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Telecommunications
Identifiers
urn:nbn:se:kth:diva-96244 (URN)
Note
QS 2012Available from: 2012-05-31 Created: 2012-05-31 Last updated: 2013-11-19Bibliographically approved
7. Calculation of signal correlation in lossy antenna arrays using scattering matrix
Open this publication in new window or tab >>Calculation of signal correlation in lossy antenna arrays using scattering matrix
(English)Article in journal (Other academic) Submitted
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Telecommunications
Identifiers
urn:nbn:se:kth:diva-96245 (URN)
Note
QS 2012Available from: 2012-05-31 Created: 2012-05-31 Last updated: 2013-11-19Bibliographically approved
8. A Simple Compact Reconfigurable Slot Antenna With a Very Wide Tuning Range
Open this publication in new window or tab >>A Simple Compact Reconfigurable Slot Antenna With a Very Wide Tuning Range
2010 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 58, no 11, 3725-3728 p.Article in journal (Refereed) Published
Abstract [en]

A simple and compact slot antenna with a very wide tuning range is proposed. A 25 mm (roughly equal to lambda(H)/8, where lambda(H) corresponds to the highest frequency of the tuning range) open slot is etched at the edge of the ground. To achieve the tunability, only two lumped elements, namely, a PIN diode and a varactor diode are used in the structure. By switching the PIN diode placed at the open end of the slot, the slot antenna can resonate as a standard slot (when the switch is on) or a half slot (when the switch is off). Continuous tuning over a wide frequency range in those two modes can be achieved by adjusting the reverse bias (giving different capacitances) of the varactor diode loaded in the slot. Through optimal design, the tuning bands of the two modes are stitched together to form a very wide tuning range. The fabricated prototype has a tuning frequency range from 0.42 GHz to 1.48 GHz with S11 better than -10 dB, giving a frequency ratio (f(R) = f(u)/f(L)) of 3.52:1. The measured full spherical radiation patterns show consistent radiation characteristics of the proposed antenna within the whole tuning range.

Keyword
Compact antenna, slot antenna, tunable antenna
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-96247 (URN)10.1109/TAP.2010.2071347 (DOI)000283940100037 ()
Note
QC 20120530Available from: 2012-05-31 Created: 2012-05-31 Last updated: 2017-12-07Bibliographically approved

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