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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.
ee,e
ehtsnn
btala
nosawpl
arop
csehsZ
seweY
Aro3hX
.gpete
hetrnh
tdsuit
g0ogign
n9mFni
el.id
eys2dr
vbec/na
aeu.k(atw
wgdast
hatonhtsu
tdlrneio
geoptgad
nnivennene
elfelalnt
eehoeeetai
vdtpihvd
afsdtanaa
ogfwr
Wra2/o-esi
rolXeflh
etcrraTy
truoteth.g
adchneaare
unuTcnn
Qid.eotne
tenihtsett
arghtrns
onneae
dcaenifeg
errihlrerln
eageeoo
Xvuvylprt
ilnoawnis
earwoode
yhpah
Dlt%em
rattltmmT
4ecnatioo.s
Vwierlcrfd.
3osardehtra
Pburtsnan
ceiorwn
esivwette
mCilmtut
miuaAeaaaon
2Tmndnpa
Vinennye
xehsietsnngh
attnaetoirt
n,reannseo
Ma2neasint
.leweeler
42arohttoelmga
Vciupnpioenl
erpgfApliu
uyimoDiataci
gtFus2/dciid
indX1.pdn
FAimin(3Ayare
nxetp
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
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