Ultrawideband Antennas - Design and Applications

202 Pages·2011·5.81 MB·English

by  Valderas

ULTRAWIDEBAND
ANTENNAS
Design and Applications
Daniel Valderas
CEIT and Tecnun, University of Navarra, Spain
Juan Ignacio Sancho
Tecnun and CEIT, University of Navarra, Spain
David Puente
Universidad Politécnica de Madrid, Spain
Cong Ling
Imperial College London, UK
Xiaodong Chen
Queen Mary, University of London, UK
Imperial College Press
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ULTRAWIDEBANDANTENNAS
Design and Applications
Copyright © 2011 by Imperial College Press
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ISBN-13978-1-84816-491-8
ISBN-101-84816-491-2
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Printed in Singapore.
Contents
Foreword v
Acknowledgements vii
Authors ix
1. IntroductiontoUltrawidebandSystems 1
CongLing
1.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 UWBSchemes . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.1 Impulseradio/timehopping . . . . . . . . . . . . . . . 3
1.2.2 Directsequence . . . . . . . . . . . . . . . . . . . . . 5
1.2.3 Frequencyhopping . . . . . . . . . . . . . . . . . . . 6
1.2.4 OFDM . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.3 IndustryStandards . . . . . . . . . . . . . . . . . . . . . . . . 11
1.3.1 Singlebandversusmultiband . . . . . . . . . . . . . . 11
1.3.2 Standards. . . . . . . . . . . . . . . . . . . . . . . . . 11
1.4 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.5 Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2. FiguresofMeritforUWBAntennas 15
DavidPuenteandDanielValderas
2.1 RequirementsforaUWBAntenna . . . . . . . . . . . . . . . 16
2.1.1 Efficiencyandmatching . . . . . . . . . . . . . . . . . 16
2.1.2 Signaldistortionanddispersion(ringing) . . . . . . . . 17
2.1.3 Stabilityoverfrequencyofthetransmission-reception
transferfunction . . . . . . . . . . . . . . . . . . . . . 17
2.2 UWBAntennaParameters . . . . . . . . . . . . . . . . . . . . 19
2.2.1 Variabilityinthefrequencydomain . . . . . . . . . . . 19
2.2.2 Variabilityinthetimedomain:Pulsedistortionparameters 23
2.2.3 Variabilityinthespacedomain . . . . . . . . . . . . . 24
2.3 SimulationintheTimeDomain . . . . . . . . . . . . . . . . . 27
xi
xii UltrawidebandAntennas:DesignandApplications
3. ClassificationofUWBAntennas 29
DavidPuenteandDanielValderas
3.1 HelicalAntennas . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2 Frequency-independentAntennas . . . . . . . . . . . . . . . . 31
3.2.1 Spiralantennas . . . . . . . . . . . . . . . . . . . . . . 31
3.2.2 Biconicalantennas . . . . . . . . . . . . . . . . . . . . 32
3.3 Log-periodicAntennas. . . . . . . . . . . . . . . . . . . . . . 34
3.4 HornAntennas . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.4.1 3Dhornantennas . . . . . . . . . . . . . . . . . . . . 36
3.4.2 2Dhornantennas . . . . . . . . . . . . . . . . . . . . 38
3.5 UWBAntennasDerivedfromResonantAntennas . . . . . . . 39
3.5.1 3Dmonopoles . . . . . . . . . . . . . . . . . . . . . . 39
3.5.2 2Dresonantantennas . . . . . . . . . . . . . . . . . . 46
3.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4. UWBMonopoleAntennaAnalysis 51
DanielValderasandJuanI.Sancho
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.2 Current-conductivePartsonPlanarMonopoleAntennas . . . . 51
4.2.1 Currentsparallelandperpendiculartothegroundplane:
Aworkinghypothesis . . . . . . . . . . . . . . . . . . 51
4.2.2 Non-radiatingcurrentsinaPMA . . . . . . . . . . . . 54
4.3 TransmissionLineModelforUWBMonopoleAntennas . . . . 56
4.3.1 Generaldescription . . . . . . . . . . . . . . . . . . . 56
4.3.2 Descriptionofthemodel . . . . . . . . . . . . . . . . 58
4.3.3 Purposeoftheanalogy. . . . . . . . . . . . . . . . . . 58
4.3.4 Graphicalapproach:TheSmithChart . . . . . . . . . . 59
4.4 DesignBasedonTLM . . . . . . . . . . . . . . . . . . . . . . 61
4.4.1 DesignofanUWB-PMAantennawithagivenbandwidth 61
4.4.2 DesignofanUWB-PMAantennahavingamaximised
bandwidth . . . . . . . . . . . . . . . . . . . . . . . . 61
4.4.3 DesignofomnidirectionalUWBantennas . . . . . . . 62
4.4.4 DesignofdirectionalUWBantennas . . . . . . . . . . 62
4.4.5 Designof2DPCBantennasforUWB . . . . . . . . . 62
4.4.6 Casestudy1:Semi-rectangularplanarmonopolecase . 62
4.4.7 Casestudy2:Broadbandmatchingofafull-rectangular
planarmonopolecase . . . . . . . . . . . . . . . . . . 65
Contents xiii
5. UWBMonopoleAntennaBandwidthSynthesis 69
DanielValderasandJuanI.Sancho
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
5.2 DefiningtheLowerLimitoftheFrequencyBand. . . . . . . . 70
5.3 ObtainingtheUpperFrequencywithStaircase
ProfileinTLM . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5.3.1 OnestepinaPMA’sprofileaccordingtoTLM . . . . . 71
5.3.2 TwostepsinaPMA’sprofileaccordingtoTLM . . . . 74
5.3.3 Analyticalestimateoftheupperlimitofthebandfora
rectangularstaircasemonopole . . . . . . . . . . . . . 75
5.4 ObtainingtheUpperFrequencythroughSlotEtching . . . . . 78
5.5 CaseStudy1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
5.5.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . 82
5.5.2 Simulationandmeasurements . . . . . . . . . . . . . . 83
5.6 CaseStudy2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
5.6.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . 86
5.6.2 Simulationandmeasurements . . . . . . . . . . . . . . 87
5.7 CaseStudy3 . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
5.7.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . 89
5.7.2 Simulationandmeasurements . . . . . . . . . . . . . . 90
5.7.3 Discussion:Impedancematchingandtransferfunction . 92
6. UWBMonopoleAntennaBandwidthMaximisation 95
DanielValderasandJuanI.Sancho
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
6.1.1 ModifyingtheprofileoftheedgeofthePMAclosestto
thegroundplane . . . . . . . . . . . . . . . . . . . . 97
6.1.2 ApplyingTLM:Changingthecharacteristicimpedance 97
6.2 CaseStudy:MaximisingAMPImpedanceBandwidth . . . . . 101
6.2.1 Lowerfrequencylimitoftheband:InitialL,W andp
parameters . . . . . . . . . . . . . . . . . . . . . . . . 101
6.2.2 Adjustingthewidth . . . . . . . . . . . . . . . . . . . 102
6.2.3 Changingtheheightpoverthegroundplane . . . . . . 102
6.2.4 Implementingabevelledcut . . . . . . . . . . . . . . . 102
6.2.5 Changingtheprofileclosetothefeed . . . . . . . . . . 105
6.2.6 Simulationandmeasurements . . . . . . . . . . . . . . 106
6.3 DiscussionofSpectralEfficiencyinBroadbandAntennas . . . 108
xiv UltrawidebandAntennas:DesignandApplications
7. UWBFoldedMonopoleAntennas 115
DanielValderasandJuanI.Sancho
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
7.2 CurrentDistributioninanAntennaFolded
alongVerticalAxes . . . . . . . . . . . . . . . . . . . . . . . 117
7.3 TLMAppliedtoanFMA . . . . . . . . . . . . . . . . . . . . 117
7.4 CaseStudy:MaximisingFMAImpedanceBandwidth . . . . . 120
7.4.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . 120
7.4.2 Simulationandmeasurements . . . . . . . . . . . . . . 123
7.4.3 Designoptions . . . . . . . . . . . . . . . . . . . . . . 133
8. RevolutionMonopoleAntennas 139
DanielValderasandJuanI.Sancho
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
8.1.1 CurrentdistributioninanRMA . . . . . . . . . . . . . 140
8.1.2 TLMappliedtoanRMA . . . . . . . . . . . . . . . . 143
8.1.3 Casestudy:MaximisingRMAimpedancebandwidth . 143
9. PrintedCircuitMonopoles 157
DanielValderasandJuanI.Sancho
9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
9.2 CurrentDistributioninaPCM . . . . . . . . . . . . . . . . . 158
9.3 TLMAppliedtoaPCM . . . . . . . . . . . . . . . . . . . . . 158
9.4 CaseStudy:TailoredBandwidthforUWBPCM . . . . . . . . 160
9.4.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . 160
9.4.2 Simulationsandmeasurements . . . . . . . . . . . . . 161
10. ApplicationsofUWBAntennas 167
XiaodongChen
10.1 UWBCommunications . . . . . . . . . . . . . . . . . . . . . 167
10.1.1 Antennasrequiredinimpulseradiosystem . . . . . . . 168
10.1.2 AntennasrequiredinMB-OFDMsystem . . . . . . . . 171
10.2 EMMeasurement . . . . . . . . . . . . . . . . . . . . . . . . 173
10.2.1 EMspectrummonitoring . . . . . . . . . . . . . . . . 173
10.2.2 EMCtesting . . . . . . . . . . . . . . . . . . . . . . . 173
10.3 MedicalImaging—BreastCancerDetection . . . . . . . . . . 174
Contents xv
10.3.1 Hornandtaperedslotantennas . . . . . . . . . . . . . 175
10.3.2 Stackedpatchantennas . . . . . . . . . . . . . . . . . 176
10.4 Radars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
10.4.1 Antennaarrayinimpulseradars . . . . . . . . . . . . . 178
10.4.2 Broadbandphasearray . . . . . . . . . . . . . . . . . 180
Bibliography 183
Index 191
Chapter 1
Introduction to Ultrawideband
Systems
Cong Ling
ImperialCollegeLondon
In this chapter, we introduce the basics of ultrawideband (UWB) systems,
the spectrum and regulations, and the advantages of UWB over conventional
narrowband systems. We outline different schemes to realise UWB: impulse
radio/timehopping,directsequence,frequencyhoppingandorthogonalfrequency
division multiplexing (OFDM). Then we show the industrial standards and
applicationsofUWB.
1.1. Overview
UWBreferstosystemswithverylargebandwidth(Ghavamietal.,2008;Aiello
and Batra, 2006; Arslan et al., 2006). This very large bandwidth offers several
advantagesincludinglowpowerconsumption,highdaterate,hightimeresolution,
low-cost implementation, obstacle penetration, resistance to interference, covert
transmission,co-existencewithnarrowbandsystemsandsoon.Suchadvantages
enableawiderangeofapplicationsofUWBtocommunications,radar,imaging
andpositioning.
Arguably, the first experiment on UWB was conducted by Hertz in 1893
(Ghavami et al., 2008). In other words, the first wireless communication system
was based on UWB. Hertz used spark gaps and arc discharges between carbon
electrodes to generate electromagnetic waves. The usage of such wideband
pulse waveforms was the dominant technique for many years after Hertz’s first
electromagneticexperiment.However,astechnologyprogressed,theemphasisof
communicationsshiftedtonarrowbandsinusoidalwaveforms.Itwasnotuntilthe
1990s that investigations into impulse radio sparked new interest in UWB. The
technologyofimpulseradiowasmadepossiblebythecorrespondingtechniques
forgeneratingshortpulsesdevelopedinthe1960s.
1
2 UltrawidebandAntennas:DesignandApplications
Perhaps the greatest advantage of UWB is most evident from the famous
Shannon formula for the capacity of a band-limited channel in Gaussian noise
(Ghavamietal.,2008):
(cid:2) (cid:3)
P
C =Wlog 1+ , (1.1)
WN
0
whereCisthechannelcapacityinbits/second(bps),W isthechannelbandwidth
inHz,P isthesignalpowerinWattsandN isthenoisepowerspectraldensityin
0
Watts/Hz.TheShannonformulashowsthat,giventhenoisepowerspectraldensity
N ofthechannel,thesignalpowerPcanbetradedoffwiththebandwidthWwhile
0
maintainingthesamechannelcapacityC.Inparticular,wecandecreaseP ifmore
bandwidth is available. On the other hand, given P the capacity C will increase
withW.Fromaninformation-theoreticperspective,thistrade-offbetweenpower
and bandwidth motivated the development of wideband communication systems
suchasspreadspectrumandUWB.Thetrade-offbetweenpowerandbandwidth
wasknowneveninanalogcommunication.Frequencymodulation(FM)usesmore
bandwidthinreturnforhighersignalqualitythanamplitudemodulation(AM).
In spread-spectrum communication, the signal power is spread over a much
widerbandwidththantheoriginal(Simonetal.,1994).However,thebandwidth
of traditional spread-spectrum communication (on the order of MHz) is not
comparable with that of UWB, which is on the order of GHz. This definition
of UWB is not unique. Federal Communications Commission (FCC) in United
States of America (USA) defines UWB as systems with bandwidth larger than
500MHzorrelativebandwidthW/fc(fcisthecarrierfrequency)largerthan20%
(Aiello and Batra, 2006). Figure 1.1 shows the spectral mask of UWB defined
by the FCC Part-15 rule and that of indoor UWB (FCC, 2002). Similar rules
have been approved in other countries of the world. In particular, a very wide
bandwidthof7.5GHzbetween3.1GHzand10.6GHzisavailableforUWBatthe
poweremissionlevel−41.3dBm/MHz.InFig.1.1,thestricterlimitationofpower
emissioninthefrequencybandbetween0.96GHzand1.61GHzisduetoexisting
servicessuchasmobilecommunications,positioningsystemsandmilitaryusage.
BecauseofthelowpowerspectraldensityofUWB,itsinterferencecanoften
beignoredbymanyexistingsystemsoccupyingthesamefrequencybands.This
property enables the unlicensed operation of UWB devices. Moreover, the short
pulses of UWB lead to multipath immunity, i.e., the propagation paths can be
identified due to its fine time resolution. This is because the resolution of the
UWBreceiverisapproximately1/W;thelargerW is,thehigheristheresolution
(Ghavami et al., 2008). The fine time resolution is very useful for ranging and
positioning.Theshortpulsesalsoenablethepenetrationthroughwallsandground.
IntroductiontoUltrawidebandSystems 3
Fig.1.1. SpectralmaskdefinedbyFCCforUWB.(FCC,2002.)
Moreover, pulse-based UWB does not require carrier modulation, thus reducing
thesizeandcostofUWBdevicescomparedtoconventionalnarrowbandsystems.
1.2. UWBSchemes
Despitebeingseenasabreakthroughtechnology,UWBiscloselyrelatedtoexisting
spread-spectrum communication. In particular, impulse radio, one of the UWB
schemes,isalsoknownastime-hopping(TH)inspread-spectrumcommunication.
Other schemes to realise UWB include direct-sequence, frequency hopping and
OFDM.Quitenaturally,UWBoffersthesamepossibilityofcode-divisionmultiple
access (CDMA) as conventional spread spectrum does, by assigning different
signaturecodestodifferentusers.Here,wepresentanoutlineofdifferentUWB
schemes. The details of UWB transceiver design and signal processing can be
foundinYangandGiannakis(2004)andQiuetal.(2005).
1.2.1. Impulseradio/timehopping
Impulse radio was the first proposed UWB scheme (Win and Scholtz, 1998;
Win et al., 2009) and has received most of the attention in the research
community. Another name for impulse radio is time-hopping. Time-hopping is
not a new technology; it has been used in spread-spectrum systems for many
decades. Figure 1.2 shows the principle of impulse radio, where each data