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Investigating and Enhancing Performance of Multiple Antenna Systems in Compact MIMO/Diversity Terminals
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Today, owners of small communicating device are interested in transmitting or receiving various multimedia data. By increasing the number of antennas at the transmitter and/or the receiver side of the wireless link, the diversity/Multiple-Input Multiple-Output (MIMO) techniques can increase wireless channel capacity without the need for additional power or spectrum in rich scattering environments. However, due to the limited space of small mobile devices, the correlation coefficients between MIMO antenna elements are very high and the total efficiencies of MIMO elements degrade severely. Furthermore, the human body causes high losses on electromagnetic wave. During the applications, the presence of users may result in the significant reduction of the antenna total efficiencies and highly affects the correlations of MIMO antenna systems. The aims of this thesis are to investigate and enhance the MIMO/diversity performance of multiple antenna systems in the free space and the presence of users.

The background and theory of multiple antenna systems are introduced briefly first. Several figures of merits are provided and discussed to evaluate the multiple antenna systems. The decoupling techniques are investigated in the multiple antenna systems operating at the higher frequencies (above 1.7 GHz) and with high radiation efficiency. The single, dual and wide band isolation enhancements are realized through the half-wavelength decoupling slot, quarter-wavelength decoupling slot with T-shaped impedance transformer, tree-like parasitic element with multiple resonances, as well as the different polarizations and radiation patterns of multiple antennas.

In the lower bands (lower than 960 MHz), due to the low radiation efficiency and strong chassis mode, the work mainly focused on how to directly reduce the correlations and enlarge the total efficiency. A new mode of mutual scattering mode is introduced. By increasing the Q factors, the radiation patterns of multiple antennas are separated automatically to reduce the correlations. With the inter-element distance larger than a certain distance, a higher Q factor also improved the total efficiency apart from the low correlation. A wideband LTE MIMO antenna with multiple resonances is proposed in mobile terminals. The high Q factors required for the low correlation and high efficiencies in mutual scattering mode is reduced with another mode of diagonal antenna-chassis mode. Hence, the bandwidth of wideband LTE MIMO antenna with multiple resonances mentioned above can be further enlarged while maintaining the good MIMO/diversity performance.

The user effects are studied in different MIMO antenna types, chassis lengths, frequencies, port phases and operating modes. Utilizing these usefully information, an adaptive quad-element MAS has been proposed to reduce the user effects and the some geranial rules not limited to the designed MAS have also been given.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , 58 p.
Series
Trita-EE, ISSN 1653-5146
Keyword [en]
Multiple antennas, planar inverted-F antenna, mutual coupling, slot antenna, compact antenna, mobile antenna, Q factors, antenna array, ultra-wideband (UWB) antenna, pattern diversity, polarization diversity, user effects, adaptive arrays, chassis mode
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-116402ISBN: 978-91-7501-600-9 (print)OAI: oai:DiVA.org:kth-116402DiVA: diva2:589729
Public defence
2013-01-28, F3, Kungliga Tekniska Högskolan, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
EU Erasmus Mundus External Cooperation Window TANDEM
Funder
EU, European Research Council
Note

QC 20130121

Available from: 2013-01-21 Created: 2013-01-18 Last updated: 2013-11-19Bibliographically approved
List of papers
1. Reducing Mutual Coupling for an Extremely Closely-Packed Tunable Dual-Element PIFA Array Through a Resonant Slot Antenna Formed In-Between
Open this publication in new window or tab >>Reducing Mutual Coupling for an Extremely Closely-Packed Tunable Dual-Element PIFA Array Through a Resonant Slot Antenna Formed In-Between
2010 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 58, no 8, 2771-2776 p.Article in journal (Refereed) Published
Abstract [en]

An efficient mutual coupling reduction method is introduced for an extremely closely packed tunable dual-element planar inverted-F antenna (PIFA) array. High isolation can be achieved through a lambda(0)/2 folded slot antenna formed by a slot on the ground plane and the neighboring edges of the two PIFAs. Direct coupling is blocked by the slot antenna through radiating the coupling power into free space. A measured isolation of more than 36.5 dB can be achieved between the two parallel individual-element PIFAs operating at 2.4 GHz WLAN band with an inter-PIFA spacing of less than 0.063 lambda(0) (center to center) or 0.0147 lambda(0) (edge to edge). Since there is only a narrow slot antenna formed between the PIFAs in the present method, the distance can be further reduced to less than 0.0016 lambda(0) (edge to edge) with the maximal isolation of better than 40 dB. Both measured and simulation results show the effectiveness of the present mutual coupling reduction method.

Keyword
Diversity antennas, mutual coupling, planar inverted F antenna (PIFA), slot antenna
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-26273 (URN)10.1109/TAP.2010.2050432 (DOI)000283432500036 ()2-s2.0-77955458626 (Scopus ID)
Note
QC 20110114Available from: 2011-01-14 Created: 2010-11-21 Last updated: 2017-12-11Bibliographically approved
2. Mutual Coupling Reduction of Two PIFAs With a T-Shape Slot Impedance Transformer for MIMO Mobile Terminals
Open this publication in new window or tab >>Mutual Coupling Reduction of Two PIFAs With a T-Shape Slot Impedance Transformer for MIMO Mobile Terminals
Show others...
2012 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 60, no 3, 1521-1531 p.Article in journal (Refereed) Published
Abstract [en]

An efficient technique is introduced to reduce mutual coupling between two closely spaced PIFAs for MIMO mobile terminals. The proposed mutual coupling reduction method is based on a T-shape slot impedance transformer and can be applied to both single-band and dual-band PIFAs. For the proposed single-band dual PIFAs, the 10 dB impedance bandwidth covers the 2.4 GHz WLAN band (2.4-2.48 GHz), and within the WLAN band an isolation of over 20 dB is achieved. Moreover, the dual-band version covers both the WLAN band and the WiMAX band of 3.4-3.6 GHz, with isolations of over 19.2 dB and 22.8 dB, respectively. The efficiency, gain and radiation patterns of the two-PIFA prototypes are verified in measurements. Due to very low pattern correlation and very good matching and isolation characteristics, the capacity performances are mainly limited by radiation efficiency. The single-band and dual-band PIFAs are also studied with respect to their locations on the ground plane. An eight-fold increase in the bandwidth of one PIFA is achieved, when the single-band PIFAs are positioned at one corner of the ground plane, with the bandwidth of the other PIFA and the good isolation unchanged.

Keyword
Antenna array mutual coupling, MIMO systems, parasitic antennas
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Telecommunications
Identifiers
urn:nbn:se:kth:diva-95124 (URN)10.1109/TAP.2011.2180329 (DOI)000302729300034 ()2-s2.0-84863229283 (Scopus ID)
Funder
Swedish Research Council, 2011-4620
Note
QC 20120515Available from: 2012-05-15 Created: 2012-05-14 Last updated: 2017-12-07Bibliographically approved
3. Ultrawideband MIMO/Diversity Antennas With a Tree-Like Structure to Enhance Wideband Isolation
Open this publication in new window or tab >>Ultrawideband MIMO/Diversity Antennas With a Tree-Like Structure to Enhance Wideband Isolation
2009 (English)In: IEEE Antennas and Wireless Propagation Letters, ISSN 1536-1225, E-ISSN 1548-5757, Vol. 8, 1279-1282 p.Article in journal (Refereed) Published
Abstract [en]

A compact printed ultrawideband (UWB) multiple-input-multiple- output (MIMO)/diversity antenna system (of two elements) with a size of 35 40 mm operating at a frequency range of 3.1-10.6 GHz is proposed. The wideband isolation can be achieved through a tree-like structure on the ground plane. The effectiveness of the tree-like structure is analyzed. Measured S-parameters show that the isolation is better than 16 dB (20 dB in most of the band) across the UWB of 3.1-10.6 GHz. The radiation patterns, gain, and envelope correlation coefficient are also measured. The proposed antenna is suitable for some portable MIMO/diversity applications.

Keyword
Diversity, isolation, multiple-input-multiple-output (MIMO), ultrawideband (UWB) antennas, diversity antenna
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-19036 (URN)10.1109/lawp.2009.2037027 (DOI)000272608300008 ()2-s2.0-77949530616 (Scopus ID)
Note

QC 20100525

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2013-11-19Bibliographically approved
4. Closely-Packed UWB MIMO/Diversity Antenna With Different Patterns and Polarizations for USB Dongle Applications
Open this publication in new window or tab >>Closely-Packed UWB MIMO/Diversity Antenna With Different Patterns and Polarizations for USB Dongle Applications
2012 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 60, no 9, 4372-4380 p.Article in journal (Refereed) Published
Abstract [en]

A closely-packed ultrawideband (UWB) multiple-input multiple-output (MIMO)/diversity antenna (of two elements) with a size of 25 mm by 40 mm is proposed for USB dongle applications. Wideband isolation can be achieved through the different patterns and polarizations of the two antenna elements. Moreover, the slot that is formed between the monopole and the ground plane of the half slot antenna is conveniently used to further enhance the isolation at the lower frequencies and to provide an additional resonance at one antenna element in order to increase its bandwidth. The underlying mechanisms of the antenna's wide impedance bandwidth and low mutual coupling are analyzed in detail. Based on the measurement results, the proposed antenna can cover the lower UWB band of 3.1-5.15 GHz, and within the required band, the isolation exceeds 26 dB. The gains and total efficiencies of the two antenna elements are also measured. Furthermore, a chassis mode can be excited when a physical connection is required between the ground planes of the two antenna elements. Without affecting the performance of the half slot element, the monopole can now cover the band of 1.78-3 GHz, apart from the UWB band. The proposed antenna structure is found to provide good MIMO/diversity performance, with very low envelope correlation of less than 0.1 across the UWB band.

Keyword
Multiple-input multiple-output (MIMO), mutual coupling, pattern diversity, polarization diversity, ultrawideband (UWB) antenna
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-103140 (URN)10.1109/TAP.2012.2207049 (DOI)000308460600037 ()2-s2.0-84866089071 (Scopus ID)
Funder
Vinnova, 2008-00970Swedish Research Council, 2010-468
Note

QC 20121009

Available from: 2012-10-09 Created: 2012-10-04 Last updated: 2017-12-07Bibliographically approved
5. Reduction of the Envelope Correlation Chofficient with Improved Total Efficiency for Mobile LTE MIMO Antennas Arroys: Mutual Scattering Mode
Open this publication in new window or tab >>Reduction of the Envelope Correlation Chofficient with Improved Total Efficiency for Mobile LTE MIMO Antennas Arroys: Mutual Scattering Mode
(English)Article in journal (Other academic) Accepted
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-116489 (URN)
Note

QS 2013

Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2013-11-19Bibliographically approved
6. Diagonal Antenna-Chassis Mode and Its Application for Wideband LTE MIMO Antennas in Mobile Handsets
Open this publication in new window or tab >>Diagonal Antenna-Chassis Mode and Its Application for Wideband LTE MIMO Antennas in Mobile Handsets
(English)Article in journal (Other academic) Submitted
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Telecommunications
Identifiers
urn:nbn:se:kth:diva-116490 (URN)
Note

QS 2013

Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2013-11-19Bibliographically approved
7. Body Loss and MIMO Performance Investigation of Different Mobil Terminal LTE MIMO Antenna Typer with User Effects
Open this publication in new window or tab >>Body Loss and MIMO Performance Investigation of Different Mobil Terminal LTE MIMO Antenna Typer with User Effects
Show others...
(English)Article in journal (Other academic) Submitted
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Telecommunications
Identifiers
urn:nbn:se:kth:diva-116495 (URN)
Note

QS 2013

Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2013-11-19Bibliographically approved
8. Adaptive Quad-Element Multi-Wideband Antenna Array for User-Effective LTE MIMO Mobile Terminals
Open this publication in new window or tab >>Adaptive Quad-Element Multi-Wideband Antenna Array for User-Effective LTE MIMO Mobile Terminals
2013 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 61, no 8, 4275-4283 p.Article in journal (Refereed) Published
Abstract [en]

An LTE MIMO antenna array, which is adaptive to the effects of the user's body, is presented for mobile terminals. The bands of 750-960 MHz and 1700-2700 MHz are covered with a good efficiency in free space. Three kinds of user effects are studied, namely, "SAM head and PDA hand," "PDA hand," and "dual hands." The array is formed by selecting the best two elements out of four, with the two ports and grounding points of the other two elements open. The user effects on MIMO channel capacity are reduced through the adaptive selection of two optimal antenna elements. The total efficiency, envelope correlation coefficient, and multiplexing efficiency are presented for the three kinds of user effects. In the lower band, the decreased correlation due to the optimal selection improves the multiplexing efficiency. The underlying physical mechanisms and some general rules are discussed. The specific absorption rate (SAR) in the "SAM head and PDA hand" case is studied. Experiments for the three kinds of user effects are also carried out.

Keyword
Adaptive arrays, handset antennas, MIMO, specific absorption rate, user effects
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Telecommunications
Identifiers
urn:nbn:se:kth:diva-116496 (URN)10.1109/TAP.2013.2260714 (DOI)000322716900039 ()2-s2.0-84881301080 (Scopus ID)
Funder
Swedish Research Council, 2011-4620
Note

QC 20130906. Updated from accepted to published.

Available from: 2013-01-21 Created: 2013-01-21 Last updated: 2017-12-06Bibliographically approved

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