Small antennas radiation performance optimization in mobile communications [Elektronische Ressource] / von Celestin Tamgue Famdie

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• Publié par: universitat_duisburg-essen
• Publié le: 01 janvier 2007
• Nombre de lectures: 33
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

Small Antennas Radiation Performance
Optimization in Mobile Communications


Von der Fakultät für Ingenieurwissenschaften der
Universität Duisburg-Essen
zur Erlangung des akademischen Grades eines
Doktors der Ingenieurwissenschaften (Dr.-Ing.)
genehmigte Dissertation

von
Dipl.-Ing. CelestinTamgue Famdie
aus
Mbo/Kamerun

Referent: Prof. Dr.-Ing. Klaus Solbach
Korreferent: Prof. Dr.-Ing. Heinz Chaloupka
Tag der mündlichen Prüfung: 30. Oktober 2007 iiAbstract
IRELESS COMMUNICATIONS haveundergoneadrasticdevelopmentinthepast
decade and have also been an important motivator for small antenna research.W
Introduction of new communications systems with wider system bands, evolu
tion from single band to multiband standard and a significant decrease in average of the
terminal size are on the roadmap of the industry. All this combined with strict limitation
duetotheprotectionofmobiledevicesusersfromradiationexposurehascreatedneedsfor
adequate antenna solutions and better understanding of small antennas on small complex
platforms. Asanswertothesegreatchallenges,apurposefulinvestigationofanewconcept
forsmallantennasdevelopmentonsmallplatformsisproposedinthisthesis.
Theperformanceofasmallantennamountedonasmallconductiveobject,suchasthe
chassisofamobilephoneisstronglyaffectedbythesizeandshapeoftheobjectaswellas
thepositionofthesmallantennaonit. Forabetterunderstandingoftheradiationproperties
of the radiating system constituted by a small antenna and the conductive chassis of a mo
bile phone device, this thesis conceptually considers the small antenna and the conductive
chassisastwodistinctiveentitiesandseparatelyinvestigatestheradiationpropertiesofthe
metalchassis. Theideahereisthatfromtheknowledgeofthechassisradiationproperties,
one easily identifies the optimal location of the small antenna on the chassis and achieves
a design of the small antenna to optimally meet some given requirements. Investigation of
theconductivechassisradiationpropertiesisbasedonthetheoryofcharacteristicmodes.
In fact, the theory of characteristic modes is a powerful analytical concept comparable
to what modal analysis represents for waveguide circuits. At a frequency of interest this
conceptprovidesaninsightonthecontributionofdifferentcharacteristicmodesintheover-
all chassis radiation properties, which inexorably leads to the knowledge of the dominant
characteristic mode. Resonant characteristic modes which dominates the radiation proper-
ties at their respective frequencies assign their radiation properties expressed in terms of
resonancefrequencyandradiationqualityfactortotheconductivechassis.
Intheframeofthiswork,anumericalevaluationofcharacteristicmodesonthesurface
of conductive chassis of mobile phones is proposed. This has been made possible through
iiithesolutionoftheresultinggeneralizedeigenvalueproblemrepresentingtheradiatingsys
tem and leading to characteristic modes. For the resolution of the resulting generalized
eigenvalue problem, an algorithm based on theQZ decomposition is conceived and a cor-
respondingsoftwareisdeveloped. Asapplication,resultsontheradiationpropertiesaswell
asoptimallocationofthesmallantenna(consideredasanexciterorcoupler)toachievean
effectivecouplingwiththechassisispresentedforgenericbar typeandfolder typephones.
Forthelattertwocasesofoperationhavebeendistinguished: theclosedandopenstates.
A simplified version of the theory of characteristic modes for the analysis of chassis
radiationpropertiesispresentedinthisthesis. Itisbasedonthefar fieldradiationproperties
of a small radiator in free space. The radiation vector is approximated by moments of
different orders depending on the shape of the chassis. This practical approach operates
by post processing output data from standard commercial electromagnetic softwares. The
purposefulutilizationandthetuningofchassismodesforthedesignofmultibandradiation
characteristicsongenericbar typeandfolder typegeometriesisdemonstrated.
ivAcknowledgments
HIS work is the result of my activities in the former company Siemens Mobile and
laterBenQMobile,whereIspentmorethantwoandhalfyears. ItstheoreticalandT
experimental aspects required the assistance of academical experts and this initi
atedandledtoacooperationwiththedepartmentofMicrowaveandRF Technologyofthe
UniversityofDuisburg Essen.
Such an achievement is the fruit of combined efforts of people at different levels, whose
contributions have directly or indirectly, negatively or positively affected this work. It is
notappropriatetoprovidedetailsaboutpeoplefromthefirstcategory.
Nevertheless I’ll like to use this opportunity to express my deepest gratitude to my mother
and to the memory of my late father for being who they are and for the great job they did
insupportingmyeducation. Thisworkshowsthatyoureffortshavenotbeenvain!
The first and foremost person from the second category is my supervisor Dr. Werner L.
Schroder¨ . Hewastheonewhohookedmeintheareaofsmallantennasandguidedmyfirst
steps in the difficult and fascinating world of research. His enlightening advice, generous
supportandunconditionalavailabilityhaveaccompagniedmeallalongfromtheearlystage
of this work based on the multipole analysis approach to the more general approach based
on the theory of characteristic modes. In many ways, he has been a wonderful supervisor.
Itwasalsohewhoconstantlyintroducedmetoothersresearchersinthefieldofantennas.
In this respect, I am deeply grateful to Prof. Dr. Ing. Klaus Solbach who also super-
visedthiswork,forthegreatinterestshown,forhisunconditionalsupportandavailability,
purposeful advice and for several discussions we had all along the whole process leading
totheresultsachieved.
My sincere and particular thanks to Prof. Dr. Ing. Heinz Chaloupka for his interest to
thiswork,forhisfastandpromptreactionassecondinstructor(Korreferent).
My deepest gratitude goes first to students who within their master thesis and internships
vconsiderablycontributedtothisproject,tomycolleguesinRF/AntennaTeamsinSiemens
Mobile in Bocholt as well as in BenQ Mobile in Kamp Lintfort and in the department of
Microwave and RF Technology of the University of Duisburg Essen for the great working
atmosphereandfortheiravailabilitytohelp.
viContents
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
ListofTables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
ListofFigures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii
1 Introduction 1
2 AnalysisandDesignMethodsforMobilePhonesAntennas 5
2.1 OptimizationCriterion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 TotalRadiatedPower(TRP) . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 ConsideredCases . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 SpecificAbsorptionRate(SAR) . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 TotalCommunicationPower(TCP) . . . . . . . . . . . . . . . . . 6
2.2.2 OptimizationCriterion . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 EquivalentCircuitModel . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.4 TheoryofCharacteristicModes . . . . . . . . . . . . . . . . . . . . . . . 9
2.4.1 OperatorEquation . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4.2ModesProblemFormulation . . . . . . . . . . . . . 9
2.4.3 ModalOrthogonalityRelations . . . . . . . . . . . . . . . . . . . 10
2.4.4Development . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4.5 TheoryofCharacteristicModesforSystemAnalysis . . . . . . . . 12
3 NumericalAnalysisofModes 15
3.1 DerivationoftheMatrixEquation . . . . . . . . . . . . . . . . . . . . . . 15
3.2 NumericalApproachfortheResolutionofEq.(3.4) . . . . . . . . . . . . . 16
3.3 AlgorithmfortheResolutionoftheGeneralizedEigenvaluesProblem . . . 18
3.3.1 Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3.2 ReductionofB toanUpperTriangularMatrix . . . . . . . . . . . 19
3.3.3oftheMatrixPairtoUpperHessenberg triangularForm 19
3.3.4 GeneralizedEigenvaluesDetermination . . . . . . . . . . . . . . . 20
viiviii CONTENTS
3.3.5 GeneralizedEigenvectorsDetermination . . . . . . . . . . . . . . 20
3.3.6 Unbalancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.4 C/C++ Programming of the Generalized Eigenvalues Problem Algorithm
andTest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.4.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.4.2 TestExample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4 RadiationPropertiesofMobilePhonesChassis 23
4.1 ChassisEigenresonantModesandfrequencies . . . . . . . . . . . . . . . . 23
4.2 NumericalEvaluationofChassisRadiationProperties . . . . . . . . . . . . 24
4.3 ChassisModalRadiationQualityFactor . . . . . . . . . . . . . . . . . . . 25
4.4 ApplicationExamples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.4.1 Bar TypePhoneStructure . . . . . . . . . . . . . . . . . . . . . . 27
4.4.2 Folder TypePhone . . . . . . . . . . . . . . . . . . . . . 29
4.4.3 Clam ShellPhoneinClosedState . . . . . . . . . . . . . . . . . . 33
5 Antenna ChassisCoupling 39
5.1 ModalDecompositio