ti無線產(chǎn)品天線設(shè)計指南

AntennaSelectionGuide

ByRichardWallace

Keywords

?AntennaSelection?AnechoicChamber?AntennaParameters

?169MHz(136-240MHzAntenna?

315MHz(273-348MHzAntenna

?433MHz(387-510MHzAntenna-868MHz(779-960MHzAntenna?915

MHz(779-960MHzAntenna?2.4GHzAntenna?

CC-Antenna-DK

1Introduction

Thisapplicationnotedescribesimportantparameterstoconsiderwhendeciding

whatkindofantennatouseinashortrangedeviceapplication.

Importantantennaparameters,differentantennatypes,designaspectsand

techniquesforcharacterizingantennasarepresented.Radiationpattern,gain,impedance

matching,bandwidth,sizeandcostaresomeoftheparametersdiscussedinthis

document.

Antennatheoryandpracticalmeasurementarealsocovered.Inadditiondifferent

antennatypesarepresented,withtheirprosandcons.Alloftheantennareference

designsavailableon/lpwarepresentedincludingtheAntennaDevelopment

Kit[29].

Thelastsectioninthisdocumentcontainsreferencestoadditionalantennaresources

suchasliterature,applicableEMsimulationtoolsandalistofantennamanufacturerand

consultants.

Correctchoiceofantennawillimprovesystemperformanceandreducethecost.

肉^TEXAS

INSTRUMENTS

Figure1.TexasInstrumentsAntennaDevelopmentKit(CC-Antenna-DK

TableofContents

KEYWORDS11INTRODUCTION12ABBREVIATI0NS33BRIEFANTENNA

THEORY43.IDIPOLE(A/2ANTENNAS43.2MONOPOLE(AMANTENNAS5

3.3WAVELENGTHCALCULATIONSFORDIPOLEINFREESPACE53.4M

AXIMUMPOWERTRANSFER(VSWR63.5ANTENNAPERFORMANCEC

ONSIDERATIONS73.6FRIISTRANSMISSIONEQUATI0N74ANTENNATYPES

84.1PCBANTENNAS10

4.1.1TIAntennaReferenceDesigns10

4.1.2IPBased1()4.2CHIPANTENNAS114.3WHIPANTENNAS114.4WIRE

ANTENNAS115ANTENNAPARAMETERS12

5.1RADIATIONPATTERNS12

5.1.1Polarization15

5.1.2GroundEffects165.2DIRECTIONALANTENNAS175.3SIZE,COST

ANDPERFORMANCE176ANTENNAMEASUREMENTS18

6.1MEASURINGBANDWIDTHWITHASPECTRUMANALYZER186.2M

EASURINGRL,IMPEDANCEANDBANDWIDTHWITHANETWORKA

NALYZER19

6.2.1MountingofcableforS11measurements19

6.2.2Calibration20

6.2.3PlacementoftheDeviceunderTest21

6.2.4InterpretingMeasurementResults21

6.2.5AntennaMatching236.30VER-THE-AIR(OTAMEASUREMENTS24

7ANTENNAREFERENCEDESIGNSAVAILABLEONWWW.TI.COM/LPW26

7.ICC-ANTENNA-DKREFERENCEDESIGNS267.22.4GHZANTENNAR

EFERENCEDESIGNS27

7.2.1SingleEndedAntennas27

7.2.2DifferentialAntennas29

7.2.3YAGIPCBDirectionalAntenna307.3SUB1GHZANTENNAR

EFERENCEDESIGNS31

7.3.1ReferenceDesignsfor868/915/955MHzAntennas31

7.3.2ReferenceDesignsfor433MHzAntennas35

7.3.3ReferenceDesignsfor315MHzAntennas36

7.3.4ReferenceDesignsfor169MHzAntennas378ADDITIONALANTENNA

RESOURCES378.1ANTENNALITERATURE378.2EMSIMULATIONTOOLS

378.3SMITHCHARTS-ANTENNAMATCHING388.4GERBERVIEWERS38

8.5E2ECOMMUNITY388.6ANTENNASUPPLIERSANDCONSULTANTS38

9SUMMARY3910REFERENCES4211GENERALINFORMATION4411.ID

OCUMENTHISTORY44

2Abbreviations

Note

Application

AN

Test

Under

AUT

Antenna

Materials

Of

BOM

Bill

Bandwidth

BW

CTIACellularTelecommunicationsIndustryAssociation

Wave

CW

Carrier

Board

Demonstration

DB

Development

Kit

DK

Note

Design

DN

Test

Under

Device

DUT

Board

EB

Evaluation

EIRPEffectiveIsotropicRadiatedPower

EM

Magnetic

Electro

Evaluation

Module

EM

Inverted-F

Antenna

IFA

Property

IPIntellectual

Scientific,

Medical

Industrial,

ISM

of

Sight

Line

LOS

Inverted-F

Antenna

Meandered

MIFA

Connected

Not

NC

NHPRPNearHorizonPartialRadiatedPower

NHPRP45NearHorizonPartialRadiatedPowerwithin45degreesangle

Air

The

OTA

Over

Board

Circuit

Printed

PCB

Radio

Frequency

RF

Loss

Return

RL

Device

Range

SRD

Short

Ratio

Wave

Standing

SWR

Instruments

TITexas

TRP

Power

Radiated

Total

Market

To

Time

TTM

VSWRVoltageStandingWaveRatio

Antenna

YAGI

Directional

3BriefAntennaTheory

Theantennaisakeycomponentforreachingthemaximumdistanceinawireless

communicationsystem.Thepurposeofanantennaistotransformelectricalsignalsinto

RFelectromagneticwaves,propagatingintofreespace(transmitmodeandtotransform

RFelectromagneticwavesintoelectricalsignals(receivemode.

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Ma2neasint

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eaeedre

3P2U6PWesmhthtnap

Figure3.EmissionPatternofaDipoleAntenna

Giventheseantennapatterns,youcanseethatadipoleantennashouldbemounted

sothatitisverticallyorientedwithrespecttothefloor.Thisresultsinthemaximum

amountofenergyradiatingoutintotheintendedcoveragearea.Thenullinthemiddleof

thepatternwillpointupanddown.

3.2Monopole

(X/4Antennas

Amonopoleantennamostcommonlyreferstoaquarter-wavelength(X/4.The

antennaisconstructedofconductiveelementswhosecombinedlengthisaboutquarter

thewavelengthatitsintendedfrequencyofoperation.Thisisverypopularduetoitssize

sinceoneantennaelementisoneX/4wavelengthandtheGNDplaneactsastheotherX/4

wavelengthwhichproducesaneffectiveX/2antenna.Therefore,formonopoleantenna

designstheperformanceoftheantennaisdependentonthegroundsize,refertoFigure4.

Allsmallantennasarederivativesofasimpledipolewhereoneelementisfoldedintothe

GNDandservesasthesecondradiator.

Figure4.MonopoleAntennaUtilizingGNDPlaneasanEffectiveX/4Antenna

Element

3.3WavelengthCalculationsforDipoleinFreeSpace

Forthesameoutputpower,sensitivityandantennagain;reducingthefrequencyby

afactoroftwodoublestherange(lineofsight.Loweringtheoperatingfrequencyalso

meansthattheantennaincreasesinsize.Whenchoosingtheoperatingfrequencyfora

radiodesign,theavailableboardspacemustalsoaccommodatetheantenna.Sothe

choiceofantenna,andsizeavailableshouldbeconsideredatanearlystageinthedesign.

Xmeters=2.99792458E8m/sec

f(GHz

Equation1.WavelengthEquation

FrequencyX/4(cmX/4(inch入(cmX(inch

GHz3.11.212.54.9

2.4

955MHz7.83.131.412.4

915MHz8.23.232.812.9

868MHz8.63.434.513.6

MHz

17.36.869.227.3

433

169MHz44.317.5177.469.8

MHz277.6109.31110.3437.1

27

Table1.VariousWavelengthsforSeveralFrequencyRanges

3.4MaximumPowerTransfer(VSWR

MoritzVonJacobi'smaximumpowertheorystatesthatmaximumpowertransfer

happenswhenthesourceresistanceequalstheloadresistance.Forcompleximpedances,

themaximumpowerdeliveredfromatransmissionlinewithimpedanceZ0toanantenna

withimpedanceZa,itisimportantthatZ0isproperlymatchedtoZa.Ifasignalwith

amplitudeVINissentintothetransmissionline,onlyapartoftheincidentwavewillbe

transmittedtotheantennaifZOisnotproperlymatchedtoZa,refertoEquation2.

Z0=Za'

Equation2.MaximumPowerTransferTheorem

Thecomplexreflectioncoefficient(「isdefinedastheratioofthereflectedwaves'

amplitudetotheamplitudeoftheincidentwave.「canbecalculatedfromtheimpedance

ofthetransmissionlineandtheimpedanceoftheantenna,asshowninEquation3.

7-7

F=_Z2

z0+z°

Equation3.ComplexReflectionCoefficient(「

Thereflectioncoefficientiszeroifthetransmissionlineimpedanceisthecomplex

conjugateoftheantennaimpedance.ThusifZO=Za'theantennaisperfectlymatched

tothetransmissionlineandalltheappliedpowerisdeliveredtotheantenna.

AntennamatchingtypicallyusesboththeReturnLossandtheVoltageStanding

WaveRatio(VSWRterminology.VSWRistheratioofthemaximumoutput(Input+「

totheminimumwaveform(Input-f,refertoEquation4.

乙+Z。

Equation4.VoltageStandingWaveRatio

ThepowerratioofthereflectedtotheincidentwaveiscalledReturnLoss;this

indicateshowmanydecibelsthereflectedwavepowerisbelowtheincidentwave.Refer

toEquation5.

z“+z0

Equation5.ReturnLoss(dB

Withantennadesign,VSWRandReturnLossareameasureofhowwellthe

antennaismatched.RefertoTable2,fortheconversionsbetweenReturnLoss,VSWR

andpercentageofpowerloss.

WhenmatchinganantennaaVSWRof1.5(RL=14dBisagoodmatch,whenthe

VSWRis>2.0(RL=9.5dBthenthematchingnetworkshouldbereviewed.VSWRof

2.0(RL=9.5dBisusuallyusedastheacceptablematchleveltodeterminethe

bandwidthoftheantenna.Mismatchingoftheantennaisoneofthelargestfactorsthat

reducethetotalRFlinkbudget.Toavoidunnecessarymismatchlosses,itis

recommendedtoaddapi-matchingnetworksothattheantennacanalwaysbematched.

IftheantennadesignisadequatelymatchedthenitjusttakesonezeroohmresistororDC

blockcaptobeinsertedintothepi-matchingnetwork.

VSWRReturn%Pbwer/ReflectionMismatch

Loss(dB)VoltaReLossCoefficientLoss(dB)

1ae0/000.000

1.1523.10.49/7.00.07.021

1.2519.11.2/11.10.111.054

1.514.04.0/20.00.200.177

1.7511.37.4/27.30.273.336

1.910.09.6/31.60316.458

2.09.511.1/33.30.333.512

2.57.418.2/42.90.429.880

3.06.025.1/50.00.5001.25

3.55.130.9/55.50.5551.6

4.04.436.3/60.00.6001.94

4.53.940.7/63.60.6362.25

5.03.544.7/66.60.6662.55

101.767.6/81.80.8184.81

200.8781.9/90.50.9057.4

1000.1796.2/98.00.98014.1

ae.000100/1001.00ae

Table2.VSWRChart

3.5AntennaPerformanceConsiderations

Thereareanumerousissuestoconsiderwhenselectingtheantenna:

?Antenna

placement

?Groundplanesfor%wavelengthantennas

?UndesiredmagneticfieldsonPCB

?Antennamismatch(VSWR

?ObjectsthatalterordisruptLineofSight(LOS

?Antennagaincharacteristics

?Antenna

bandwidth

?AntennaRadiationEfficiency

3.6FriisTransmissionEquation

FriisequationistheprimarymathmodeltopredictingLineofSightcommunication

links.Thisisaveryelementaryequationandhasbeenexpandedtoincludeheightof

antennaabovegroundanddifferenceinTXandRXantennas.Theformulaisvery

accurateoncealltheconstantshavebeenentered.Pleasereferto[28]forfurther

informationconcerning“RangeMeasurementsinanOpenFieldEnvironment”.

VSWRReturn%Pbwer/Refle.

Loss(dB)VoltageLossCoeffi

13C0/00

1.1523.10.49/7.00.(

Equation6.FriisTransmissionEquation

X=WavelengthinMeters

Pr=ReceivedPowerindBm

Pt=TransmitPowerindBm

Gt=TransmitAntennaGainindBi

Gr=ReceiveAntennaGainindBi

R=DistancebetweenAntennasinMeters

4AntennaTypes

Thereareseveralantennatypestochoosefromwhendecidingwhatkindofantenna

touseinanRFproduct.Size,costandperformancearethemostimportantfactorswhen

choosinganantenna.Thethreemostcommonlyusedantennatypesforshortrange

devicesarePCBantennas,chipantennasandwireantennas.Table3showstheprosand

consforseveralantennatypes.

AntennatypesProsCons

PCBantenna*Verylowcost

?Goodperformanceat

>868MHz

?Smallsizeathigh

frequencies

?Standarddesign

antennaswidely

available?DifficulttodesignsmallandefficientPCBantennasat<433MHz

?Potentiallylargesizeatlowfrequencies

Chipantenna?Smallsize

?ShortTTMsince

purchasingantenna

solution,Mediumperformance?Mediumcost

Whipantenna?Goodperformance

?ShortTTMsince

purchasingantenna

solution?Highcost

?Difficulttofitinmanyapplications

Wireantenna?Verycheap?Mechanicalmanufacturingof

antenna

IPbasedantenna

?SupportfromIP

company

?Highcostcomparedtostandard

freePCBantennadesigns.

?SimilarcosttoChipantennaTable3.ProsandConsforDifferentAntenna

Solutions

Itisalsocommontodivideantennasintosingleendedantennasanddifferential

antennas.Singleendedantennasarealsocalledunbalancedantennas,whiledifferential

antennasareoftencalledbalancedantennas.Singleendedantennasarefedbyasignal

whichisreferencedtogroundandthecharacteristicinputimpedancefortheseantennasis

usually50ohms.MostRFmeasurementequipmentsarealsoreferencedto50ohms.

Therefore,itiseasytomeasurethecharacteristicofa50ohmantennawithsuch

equipment.

HowevermanyRFIC'shavedifferentialRFportsandatransformationnetworkis

requiredtouseasingleendedantennawiththeseIC's.Suchanetworkiscalledabalun

sinceittransformsthesignalfrombalancedtounbalancedconfiguration.Figure5shows

asingleendedantennaandadifferentialantenna.

SingleEnded

AntennaDifferentialAntenna

Figure5.SingleEndedandDifferentialAntenna

Theantennaspresentedinthisdocumentareforthelicensefreeworldwideband

2.4000GHz-2.4835GHzbandandtheallthestandardfrequencybandsatsub1GHz.

Forthesub1GHzbands;thereisusuallya"low"sub1GHzbandanda"high”sub1

GHzband.

The“high"sub1GHzbandinEuropecovers863-870MHz,theUScovers902-928

MHzbandandtheJapaneseband955MHz.TheEuropeanbandisusuallyreferredtoas

the“868MHzband"andtheUSbandiscommonlydesignatedthe“915MHzband”.Itis

oftenpossibletoachievegoodperformancewiththesameantennaforboththeEuropean

868MHz,US915MHzandJapanese955MHzbandsbytuningtheantennalengthor

changingthevaluesofthematchingcomponents.Suchantennasarecalled

"868/915/955"MHzantennas^^inthisdocument.

The44low^^sub1GHzbandinEuropecovers433.050-434.790MHz,theUScovers

300-348MHzband.TheEuropeanbandisusuallyreferredtoasthe“433MHzband”

andtheUS

bandiscommonlydesignatedthe“315MHzband”.

Antennas

4.1PCB

Ourambitionistoprovideexcellentantennareferencedesignsandapplicationnotes

sothedesign-inprocesswillbeeasierandquicker.WithRFdesigns,theantennadesign

isacriticalstagetobeabletoachievethebestpossiblelinkbudgetforaspecific

application.Aspreviouslymentionedin3.5,therearemanyconsiderationswhen

choosingthetypeofantenna.

Theantennaapplicationnotesareupdatedonaregularbasiswithnewdesigns.The

TIantennadesignsthatarereleasedarefreeofchargeandcanbeuseddirectlyinthe

finalapplicationdesign.InadditiontothesefreeTIantennadesigns,wealsohave

specificantennasdesignsthatareIPbased.TheantennaIPcompanyusuallyhasa

specificdesignprofilesuchasdirectivityorcompactdesignforexample.

Theantennainthebasicform,PIFA,patch,spiraletcisgenerallyfreefrompatent

infringementbecausethesearewellknowndesignsthathavebeenaroundformanyyears.

Whentheantennaisadaptedfromthe"standardformat";thentheantennasaremorethan

likelyprotectedthroughpatents.Itisimportanttokeepthisinmindwhendevelopinga

newantenna.Manyantennapatentscollidewitheachotherandwhichcompanyhadthe

originalIP,andiftheIPisvalidcanbealongdiscussion.Itisadvisabletokeepthe

standardtextbookantennadesignswhendevelopinganantennatoavoidanylegal

discussions.

4.1.1TIAntennaReferenceDesigns

DesigningaPCBantennaisnotstraightforwardandusuallyasimulationtoolmust

beusedtoobtainanacceptablesolution.Inadditiontoderivinganoptimumdesign,

configuringsuchatooltoperfonnaccuratesimulationscanalsobedifficultandtime

consuming.Itisthereforerecommendedtomakeanexactcopyofoneofthereference

designsavailableat/lpw,iftheavailableboardspacepermitssuchasolution.

Seesection7foradescriptionoftheavailablereferencedesigns.

TheCC-Antenna-DK[43]contains13lowcostantennasand3calibrationboards.

Theantennascoverthefrequencyrangeaslowas136MHzto2.48GHz;refertoFigure1.

TheantennadesignsfromtheCC-Antenna-DKaresummarizedin7.1.

Iftheapplicationrequiresaspecialtypeofantennaandnoneoftheavailable

referencedesignsfitstheapplication,itcouldbeadvantageoustocontactanantenna

consultantorlookfbrothercommerciallyavailablesolutions.Table8listsafew

companiesthatcanoffersuchservices.

Based

4.1.2IP

TherearemanyIPantennadesigncompaniesthatselltheirantennadesign

competencethroughIP.Sincethereisnosiliconorfirmwareinvolved;theonlywayfor

theantennaIPcompaniestoprotecttheirantennadesignisthroughpatents.Purchasinga

chipantennaorpurchasinganIPfbrtheantennadesignissimilarsincethereisan

externalcostfortheantennadesign.

IPbasedantennasfromPinyonarespecificallydesignedfordirectionaloperation

(5.2andFractusistargetingcompactdesignsaswellassalesoftheirstandardchip

antennas.

AnalternativetotheIPPinyonantennareferencedesigns[20],[21],[22]&[23]can

beastandardpatchantennaorYAGIantenna(refertoSection7.2.3whichwillalsogive

directivitybutwithnoIPcostattached.A2.4GHzpatchantennawillbereleasedasa

referencedesign.Thepatchantennamainlyradiatesinjustonedirection(onemainlobe

whereastheIPPinyonantennahastwolobes,similartoafigureeight.TheYAGI

antennausuallyhasahighergainthanthepatchantennaandistypicallylargerinsizeas

well.

4.2Chip

Antennas

Iftheavailableboardspacefortheantennaislimitedachipantennacouldbeagood

solution.Thisantennatypeallowsfbrsmallsizesolutionsevenforfrequenciesbelow1

GHz.ThetradeoffcomparedtoPCBantennasisthatthissolutionwilladdBOMand

mountingcost.Thetypicalcostofachipantennaisbetween$0.10and$0.50.Evenif

manufacturersofchipantennasstatethattheantennaismatchedto50ohmsforacertain

frequencyband,itisoftenrequiredtouseadditionalmatchingcomponentstoobtain

optimumperformance.Theperformancenumbersandrecommendedmatchinggivenin

datasheetsareoftenbasedonmeasurementsdonewithatestboard.Thedimensionsof

thistestboardareusuallydocumentedinthedatasheet.Itisimportanttobeawarethat

theperformanceandrequiredmatchingwillchangeifthechipantennaisimplementedon

aPCBwithdifferentsizeandshapeofthegroundplane.

Antennas

4.3Whip

Ifgoodperformanceisthemostimportantfactor,sizeandcostarenotcritical;an

externalantennawithaconnectorcouldbeagoodsolution.Ifaconnectorisusedthento

passtheregulations,conductedemissiontestsmustalsobeperformed.Thewhipantenna

shouldbemountednormallyonthegroundplanetoobtainbestperformance.Whip

antennasaretypicallymoreexpensivethanchipantennas,andwillalsorequirea

connectorontheboardthatalsoincreasesthecost.Noticethatinsomecasesspecial

typesofconnectorsmustbeusedtocomplywithSRDregulations.Formoreinformation

aboutSRDregulationspleaserefertof1]and[2].

Antennas

4.4Wire

Forapplicationsthatoperateinthelowerbandsofthesub1GHzsuchas315MHz

and433MHz;theantennaisquitelarge,refertoTable1.Evenwhentheearthplaneis

utilizedforhalfoftheantennadesign;theoverallsizecanbelargeanddifficulttoput

ontoaPCB.Whatcanbedoneforthisfrequencyrangewhichispracticalandcheap;a

wirecanbeusedfortheantennaandthewirecanbeformedaroundthemechanical

housingoftheapplication.

Theprosofsuchasolutionarethepriceandgoodperformancecanbeobtained.The

consarethevariationsofthepositioningoftheantennainthemechanicalhousingwill

havetobecontrolledsothattheantennawillnotvarytoomuchduringvolume

production.

Astandardcablecanbeusedasanantennaifcuttotherightlength,refertoTable1.

Theperformanceandradiationpatternwillchangedependingonthepositionofthecable.

Ifthistypeofantennaisusedthenitisgoodpracticetokeepthefirstpartofthecable

whichisclosesttothefeedpointintoamorecontrolledpositionsothematchingwillnot

beaffectedtoomuchwhentheremainingcableantennachangespositionswhentouched

ormoved.

5AntennaParameters

Thereare