Presenter:MiZhiqiangHunanModernLogisticsCollegeTheperformanceanddeploymentofRFIDantennaCONTENTS1TherelationshipbetweenperformanceofRFIDread/writeandRFIDantenna3TheconfigurationofcommonlyusedRFIDantenna2ThemajorparametersofRFIDantenna4TheroleandpositionofRFIDantenna5FactorsaffectingtheperformanceoftheRFIDantennaTherelationshipbetweenperformanceofRFIDread/writeandRFIDantenna01Anantennaisadevicethatconvertsthereceivedelectromagneticwaveintocurrentsignalorconvertscurrentsignalintoanelectromagneticwave.InRFIDsystems,antennasareincludedinboththeRFtagandthereader.TheantennacanbeintegratedintotheRFtagandreader,oritcanbeplacedseparatelyfromtheRFtagandreader.InordertoensurethenormaloperationoftheRFIDsystem,theantennaperformanceofthetagandreadermustmeetcertainrequirements.TherelationshipbetweenperformanceofRFIDread/writeandRFIDantenna011)TheantennaintheRFtagsIntheradiofrequencydevices,whentheoperatingfrequencyisincreasedtothemicrowaveregion,itbecomesdifficulttomatchbetweentheantennaandthetagchip.Theroleoftheantennaistoensureenergyaslargeaspossibleintoandoutofthetagchip;forshispurpose,theantennadesign,freespaceandconnetedtagchipsmustbetakeintoconsiderationcomprehensively.(1)Necessaryrequirementsfortagantenna1Smallenoughtobeattachedtothedesireditem;2Directionalitywithomnidirectionalorhemisphericalcoverage;3Toprovidethesignalaslargeaspossibletothechipofthetag;4Regardlessofthepositionoftheitem,thepolarizationoftheantennacanmatchtheinterrogationsignalofthecardreader;5Robust;6Verycheap.(2)Factorstobeconsideredwhenchoosingantenna1.Typesoftheantenna2.Theimpedanceoftheantenna;3.Theperformanceoftheradioappliedtotheitem.TherelationshipbetweenperformanceofRFIDread/writeandRFIDantenna012)TheantennaofreaderThereadersoftheRFsystemmustemitenergythroughtheantennatoformanelectromagneticfield,andthenidentifytheRFtagthroughtheelectromagneticfield.ItcanbesaidthattheelectromagneticfieldformedbytheantennaisthereadablespaceoftheRFIDsystem,andanyRFIDsystemshouldcontainatleastoneantenna(whetherbuilt-inorexternal)toemitandreceiveRFsignals.ForsomeRFIDsystems,oneantennaemitsandreceivesignalssimultaneously,andforsomeotherRFIDsystems,therearetwoantennasofwhichoneantennaemitsenergyandtheotherreceivessignals.whichtypesofantennawillbechosenshouldbebasedonthespecificcircumstances.Inaninductivelycoupledradiofrequencyidentificationsystem,thereaderantennaisusedtogeneratemagneticflux,andthemagneticfluxisusedtosupplypowertotheradiofrequencytagandtotransferinformationbetweenthereaderandtheradiofrequencytag.ThemajorparametersofRFIDantenna021)ElectromagneticradiationWhenalternatingcurrentflowsonthewire,electromagneticwaveradiationisgenerated,andradiationcapabilityisrelatedtothelengthandshapeofthewire.Asshowninfigure(a),ifthedistancebetweenthetwowiresisveryclose,theelectricfieldistrappedbetweenthetwowires,sotheradiationisveryweak;ifthedistanceofthetwowiresarealittlefaraway,asshowninfigure(b),theelectricfieldcouldbespread,asaresult,theradiationwouldbeenhanced.FigureDiagramofradiationofelectromagneticwavesItmustbepointedoutthatwhenthelengthofthewireismuchsmallerthanthewavelength,theradiationisveryweak;whenthelengthofthewireiscomparabletothewavelength,thecurrentonthewiregreatlyincreases,therebyformingstrongerradiation.ThemajorparametersofRFIDantenna02ThemajorparametersofRFIDantenna1)Electromagneticradiation2)SymmetricalvibratorofRFIDantenna3)DirectionalityoftheRFIDantenna4)InputtingimpedanceoftheantennaZin5)Standingwaveratio6)Returnloss7)Polarizationoftheantenna8)Antennagain9)Thelobewidthoftheantenna10)Front-BackRatio11)Uppersidelobesuppression12)Downtiltoftheantenna13)Antennaoperatingfrequencyrange(bandwidth)14)ReflectionlossThemajorparametersofRFIDantenna022)SymmetricalvibratorofRFIDantennaThesymmetricalvibratorisaclassical,themostwidelyusedantenna.Thesinglehalf-wavesymmetryoscillatorcanbeusedsimplyorindependentlyorasafeedforaparabolicantenna.Apluralityofhalf-wavesymmetryoscillatorscanalsobeusedtoformanantennaarray.Avibratorwiththesamelengthofbotharmsiscalledasymmetricalvibrator.Avibratorofwhichthelengthofarmis1/4wavelengthandthefulllengthequals1/2wavelengthiscalledahalf-wavesymmetricvibrator,asshowninfigure(a).wavelengthwavelengthwavelengthSymmetricoscillatorHalf-wavesymmetricoscillatorThemajorparametersofRFIDantenna02Inaddition,thereisaspecial-shapedhalf-wavesymmetricvibrator,whichcanbeseenasafull-wavesymmetricvibratorfoldedintoanarrowrectangularframe,andthetwoendsofthefull-wavesymmetricvibratorarestacked,andthenarrowrectangularframeiscalledfoldedvibrator.Itshouldbenotedthatthelengthofthefoldedvibratorisalso1/2wavelength,soitiscalledahalf-wavefoldedvibrator,asshowninFigure(b).wavelengthSymmetricoscillatorHalf-wavesymmetricoscillatorThemajorparametersofRFIDantenna023)DirectionalityoftheRFIDantennaTheRFIDantennacouldbeclassifiedintoemittingantennaandreceivingantenna.Amongthem,thefirstfundamentalfunctionsoftheemittingantennaistoradiatetheenergyobtainedfromthefeedertothesurroundingspace.Thesecondfunctionistoradiatemostoftheenergyinthedesireddirection.Theverticallyplacedhalf-wavesymmetryvibratorhasathree-dimensionalpatternofaflat"breadnut"shape,asshownin(a).Althoughthestereoscopicpatternisstrong,itisdifficulttodraw.Figures(b)and(c)showitstwoprincipalplanepatterns,andtheplanepatterndescribesthedirectivityoftheantennaonaspecifiedplane.Itcanbeseenfromthefigure(b)thattheradiationintheaxialdirectionofthevibratoriszeroandthemaximumradiationdirectionisonthehorizontalplane;andasshownfromthediagram(c),theradiationinalldirectionsonthehorizontalplaneissame(a)Stereoscopicpattern(b)Verticalplanepattern(c)HorizontalplanepatternThemajorparametersofRFIDantenna023)DirectionalityoftheRFIDantennaThedirectionalityoftheantennaisenhanced,andanumberofsymmetricaloscillatorarrayscancontroltheradiation,creatinga"flatbagel"thatfurtherconcentratesthesignalinthehorizontaldirection.Thefigurebelowshowsthestereoandverticalplanedirectionsoffourhalf-wavesymmetryoscillatorsarrangedalongaverticallineintoaverticalquaternionarray.(a)Stereoscopicpattern(b)VerticalplanepatternFigureDirectionalityoftheRFIDantenna3)DirectionalityoftheRFIDantennaThereflectorcouldbeusedtomanipulatetheradiantenergytoasingledirection,andaplanarreflectorononesideofthearraytoformasectorcoveringtheantenna.Thelowerhorizontalpatternillustratestheeffectofthereflectivesurface-thereflectivesurfacereflectspowertotheone-sideddirection,increasingthegain.ThemajorparametersofRFIDantenna02FigureDiagramofreflectivesurfaceThemajorparametersofRFIDantenna02（1)InputtingimpedanceoftheantennaZin

Definition:Theratiooftheinputvoltageoftheantennafeedtotheinputcurrentiscalledtheinputimpedanceoftheantenna.TheinputimpedancehasaresistancecomponentRinandareactivecomponentXin,thatis,Zin=Rin+jXin.Thepresenceofthereactivecomponentreducestheextractionofthesignalpowerfromthefeedertotheantenna.Therefore,thereactivecomponentmustbemadeaszeroaspossible,thatis,theinputimpedanceoftheantennashouldbeaspureaspossible.Infact,evenanantennathatiswelldesignedanddebuggedalwayshasasmallreactivecomponentinitsinputimpedance.Theinputimpedanceisrelatedtothestructure,sizeandoperatingwavelengthoftheantenna.Thehalf-wavesymmetryoscillatoristhemostimportantbasicantenna,anditsinputimpedanceisZin=73.1+j42.5(ohms).Whenthelengthisshortened(3~5)%,thereactivecomponentcanbeeliminated,andtheinputimpedanceoftheantennaispureresistance.TheinputimpedanceatthistimeisZin=73.1(Europe),(nominally75ohms).ThemajorparametersofRFIDantenna02（2)StandingwaveratioInthecaseofmismatch,therearebothincidentandreflectedwavesonthefeeder.Wherethephaseoftheincidentwaveandthereflectedwavearethesame,thevoltageamplitudeisaddedtothemaximumvoltageamplitudeVmaxtoformanantinode;andintheoppositephaseoftheincidentwaveandthereflectedwave,thevoltageamplitudeissubtractedtotheminimumvoltageamplitudeVmintoformanode.Theamplitudevaluesofotherpointsarebetweentheantinodeandthenode.Thissyntheticwaveiscalledastandingwave.ThemajorparametersofRFIDantenna02TheratioofthereflectedwavevoltagetotheamplitudeoftheincidentwavevoltageiscalledthereflectioncoefficientandisdenotedasR:

Reflectedwaveamplitude(ZL-Z0）

R=

=(2.2)Incidentwaveamplitude(ZL+Z0)TheratiooftheantinodevoltagetotheamplitudeofthenodevoltageiscalledtheVSWR,alsocalledthevoltagestandingwaveratio,whichisrecordedasVSWR.

AntinodevoltageamplitudeVmax(1+R)VSWR==(2.3)

NodevoltageamplitudeVmin(1-R)TheclosertheterminalloadimpedanceZListothecharacteristicimpedanceZ0,thesmallerthereflectioncoefficientRis,andthecloserthestandingwaveratioVSWRisto1,thebetterthematching.（3)StandingwaveratioThemajorparametersofRFIDantenna02（4)Returnloss

Itisthereciprocaloftheabsolutevalueofthereflectioncoefficientandisexpressedindecibels.Thevalueofthereturnlossisbetween0dBandinfinity.Thelargerthereturnloss,theworsethematch.Thelargerthereturnloss,thebetterthematch.0meanstotalreflection,andinfinitymeanscompletematch.Inmobilecommunicationsystems,thereturnlossisgenerallyrequiredtobegreaterthan14dB.EmissionpowerEmissionpowerEmissionpowerEmissionpowerThemajorparametersofRFIDantenna02（4)PolarizationoftheantennaThepolarizationoftheantennaisrelatedtotheantennaradiateselectromagneticwavestothesurroundingspace.Electromagneticwavesarecomposedofanelectricfieldandamagneticfield.Itisstipulatedthatthedirectionoftheelectricfieldisthepolarizationdirectionoftheantenna,whichisthedirectionoftheelectricfieldformedwhentheantennaisradiated.Whenthedirectionoftheelectricfieldisperpendiculartotheground,theelectricwaveiscalledaverticallypolarizedwave;whenthedirectionoftheelectricfieldisparalleltotheground,theelectricwaveiscalledahorizontallypolarizedwave.Thecommonlyusedantennasareunipolar.Thefigurebelowshowstwobasicsingle-polarizationcases:verticalpolarization-themostcommonusedone;horizontalpolarization-isalsousedone(a)verticalpolarization(b)horizontalpolarization

FigurePolarizationoftheantennaThemajorparametersofRFIDantenna02（4)PolarizationoftheantennaDual-polarizedantennas,thefollowingfigureshowstwoothersingle-polarizationcases:+45°polarizationand-45°polarization,whichareusedonlyinspecialcases.Thus,therearefourtypesofsinglepolarization,seethefigurebelow.Combiningtwopolarizedantennasofverticalpolarizationandhorizontalpolarization,orcombiningtwopolarizationantennasof+45°polarizationand-45°polarization,constitutesanewantenna.-Dualpolarizedantenna.FigureTwosinglepolarizationThus,therearefourtypesofsinglepolarization,asshownbelow.TheCombinationoftwopolarizedantennasofverticalpolarizationandhorizontalpolarization,orcombinationoftwopolarizedantennasof+45°and-45°polarization,constitutesanewantenna.-dualpolarizedantenna.FigureTwotypesofpolarizationThemajorparametersofRFIDantenna02（4）PolarizationoftheantennaThefigurebelowshowstwosingle-polarizedantennasmountedtogethertoformadual-polarizedantenna.Notethatadual-polarizedantennahastwoconnectors.Adualpolarizedantennaradiates(orreceives)twowavesthatareorthogonaltoeachother(vertical)inspace.FigureDualpolarizedantennaThemajorparametersofRFIDantenna02（4)PolarizationoftheantennaForpolarizationloss,verticallypolarizedwavesarereceivedbyanantennahavingverticalpolarizationcharacteristics,andhorizontallypolarizedwavesarereceivedbyanantennahavinghorizontalpolarizationcharacteristics.Theright-handcircularlypolarizedwaveisreceivedbyanantennahavingaright-handedcircularpolarizationcharacteristic,andtheleft-handedcircularlypolarizedwaveisreceivedbyanantennahavingaleft-handedcircularpolarizationcharacteristic.Completepolarizationisolationcouldnotexistinreality.Thesignalfedintoapolarizedantennawillalwaysappearalittlebitinanotherpolarizedantenna.Inthedual-polarizedantenna,thepowerinputtedintoverticallypolarizedantennais10W,however,theoutputpowermeasuredattheoutputofthehorizontallypolarizedantennais10mW.ThemajorparametersofRFIDantenna02（5)AntennagainAntennagainisameasureofthecapabilityofanantennatotransmitandreceivesignalsinaparticulardirection.Itisoneofthemostimportantparametersforselectingabasestationantenna.Antennagainreferstotheratioofthepowerdensityofthesignalproducedbytheactualantennaatthesamepointinspaceastheidealradiatingelement,undertheconditionofequalinputpower.Itquantitativelydescribestheextenttowhichanantennaconcentratestheinputpower.Thegainisobviouslycloselyrelatedtotheantennapattern.Thenarrowerthemainlobeofthepattern,thesmallerthesidelobesandthehigherthegain.Thephysicalindicationofthegaincanbeunderstoodinthisway-togenerateasignalofacertainsizeatacertaindistanceoveracertaindistance,ifanidealnon-directionalpointsourceisusedasthetransmittingantenna,100Wofinputpowerisrequired;howeverWhenadirectionalantennawithG=13dB=20isusedasthetransmittingantenna,theinputpoweronlyneeds100/20=5W.Inotherwords,Thegainofanantennaisamultipleoftheinputpowerthatisamplifiedcomparedtotheidealpointsourceofnon-directionalityinthedirectionofmaximumradiation.ThemajorparametersofRFIDantenna02（5)AntennagainSeveralapproximatecalculationsforantennagain1)Thenarrowerthemainlobewidthoftheantenna,thehigherthegain.Foratypicalantenna,thegaincanbeestimatedusingthefollowingequationG(dBi)=10Lg{32000/(2θ3dB,E×2θ3dB,H)}Where,2θ3dB,Eand2θ3dB,Harethelobewidthsoftheantennaonthetwoprincipalplanesrespectively;32000istheempiricaldatacalculated.2)Foraparabolicantenna,thegaincanbeapproximatelycalculatedbythefollowingequation:G（dBi）=10Lg{4.5×（D/λ0）2}WhereDistheparabolicdiameterandλ0isthecentraloperatingwavelength;whereistheempiricaldatafromthestatistics.3)Fortheuprightomnidirectionalantenna,thereisanapproximatecalculationG（dBi）=10Lg{2L/λ0}}WhereListhelengthoftheantennaandλ0isthecenteroperatingwavelength;ThemajorparametersofRFIDantenna02（6)ThelobewidthoftheantennaThelobewidthisaveryimportantparametercommonlyusedindirectionalantennas.Itreferstothewidthoftheantennaformedintheradiationpatternbelowthepeakof3dB(Theradiationpatternoftheantennaisanindicatorofthecapabilityoftheantennatotransmitandreceivesignalsinalldirections.Usuallygraphicallyexpressedastherelationshipbetweenpowerintensityandangle).Forthelobewidthofanantenna,thepatternusuallyhastwoormoreflaps,ofwhichtheflapwiththehighestradiationintensityiscalledthemainlobe,andtheotherflapiscalledthesidelobe.AsshowinFigurea,theanglebetweenthetwopointswheretheradiationintensityisreducedby3dB(halfthepowerdensityisreduced)onbothsidesofthemaximumradiationdirectionofthemainlobeisdefinedasthelobewidth(alsoknownasbeamwidthormainlobewidthorhalfpowerangle).Thenarrowerthelobewidth,thebetterthedirectivity,andthefarthertheactiondistanceis,thestrongertheanti-interferencecapabilityis.Figure(a)the3dBlobewidthoftheantennaThemajorparametersofRFIDantenna02Anothertypeoflobewidthiscalled10dblobewidth.AsshowinFigureb,theanglebetweenthetwopointswheretheradiationintensityisreducedby10dB(halfthepowerdensityisreduced)onbothsidesofthepattern.（6)ThelobewidthoftheantennaFigure(b)the10dblobewidthoftheantenna(7)Front-BackRatioItshowshowwelltheantennasuppressesthebacklobes.Whentheantennawithlowfront-to-backratioisselected,thebackflapoftheantennamayhaveacross-overcoverage,resultinginachaoticswitchingrelationshipandadroppedcall.Anantennawithafront-to-backratioof30shouldbepreferred.Forthefront-backratio,itreferstotheratioofthemaximumvalueoftheanteriorandposteriorlobesinthepatternandisrecordedasF/B.Thelargerthefront-to-backratio,thesmallerthebackwardradiation(orreception)oftheantenna.Thecalculationofthefront-to-frontratioF/Bisquitesimple---F/B=10Lg{(forwardpowerdensity)/(backwardpowerdensity)}.Whenthefront-to-backratioF/Boftheantennamustbemeetsomecriteria,thetypicalvalueis(18～30)dB,andinsomespecialcircirmstances,itmustreach(35to40)dB.ThemajorparametersofRFIDantenna02ForwardpowerBackwardpowerFigureDirectionalityofthefrond-backratioThemajorparametersofRFIDantenna02（9)DowntiltoftheantennaInordertoensurethemainlobetopointtotheground,theantennaneedstobeproperlytilteddownduringinstallation.（10)Antennaoperatingfrequencyrange(bandwidth)Regardlessoftransmittingantennaorreceivingantenna,theyalwaysfunctioninacertainfrequencyrange(bandwidth),andthebandwidthoftheantennahastwodifferentdefinitions:OnereferstotheworkingfrequencybandwidthoftheantennaundertheconditionofstandingwaveratioSWR≤1.5;Theothermeansthattheantennagaindropsbyabandwidthof3db.Inthemobilecommunicationsystem,usuallyitreferstotheformer.Specifically,thebandwidthoftheantennaistheoperatingfrequencyrangeoftheantennawhenthestandingwaveratioSWRoftheantennadoesnotexceed1.5.（11)ReflectionlossAsmentionedabove,whenthefeederandtheantennaarematched,thereisnoreflectedwaveonthefeeder,andonlytheincidentwave,thatis,thewavetransmittedonthefeederisonlythewavetravelinginthedirectionoftheantenna.Atthistime,thevoltageandcurrentamplitudearesameacrossthefeeder,andtheimpedanceofanypointonthefeederisequaltoitscharacteristicimpedance.Intheimagetotheright,duetothedifferenceinimpedancebetweentheantennaandthefeeder,oneis75ohmsandtheotheris50ohms,sotheimpedanceisnotmatched.ThemajorparametersofRFIDantenna02FigureDiagramofreflecti