講義教案成果heikkinen 2004 low profile circularly polarize

162 IEEEMICROWAVEANDWIRELESSCOMPONENTSLETTERS,VOL.14,NO.4,APRIL2004

Low-ProfileCircularlyPolarizedRectifyingAntennaforWirelessPowerTransmissionat5.8GHz

JoukoHeikkinen,Member,IEEE,andMarkkuKivikoski,Member,IEEE

—PortabledevicesoperatingwithoutbatteriesaresometimesdesiredinwirelessapplicationssuchasRFID(RadioFrequencyIdentification)andemetry.Anovelcircularlypolarizedshortedannularring-slotrectenna(rectifyingantenna)ona0.5mmthickflexiblemicrowavelaminateisproposedforthepoweringofthesedevices.Outputdcvoltageof1.3Vandaxialratioof1.5dBweremeasuredwhen32dBmmicrowavepowerwastransmittedat5.8GHzoveradistanceof2m.Comparingtheresultswitharectennadesignedonathickrigidlaminate,similarperformancewasobserved.

IndexTerms—Circularpolarization,rectifier,slotantenna.

A

Introduction

RECTENNAisaRFpowerreceiverthatconvertsthere-ceivedpowerintodcpowerthatcanthenbeconsumed,

e.g.,byanactiveRFIDtag[1]integratedintotherectennastruc-ture.Theadvantageofacircularlypolarized(CP)rectennaoveralinearlypolarizedoneisthatnearlyconstantdcoutputcanbeachievedeveniftherectenna’srotationangle,relativetothetransmitter,changes.

SeveralantennasforCPradiationhavebeendesignedoverthelastfewyearsusingacircularring,e.g.,withstriplinehy-bridcouplerfeedat2.45GHz[2],withmicrostripfeedat1.5GHz[3],andwithconarwaveguideandcoaxiallinefeedat

2.45GHz[4].Tothebestofourknowledge,fewrectennaforCPradiationhavebeenproposedsofar[5],[6].Furthermore,theserectennasareintendedfortheoperationatrelativelyhighpowerdensities.

Anannularring-slotrectennadesignedforlowpowerden-sitiesandoperatingat5.2GHzwasintroducedin[7].Inthisletter,anenhanceddesignoperatingat5.8GHzisproposedandtheperformanceofthetwodesignsiscompared.

TestStructure

Rectennawasdesignedonathinhigh-frequencylaminateRO3003( , , ,copperthickness35).ThelayoutoftherectennaisshowninFig.1.Antennaandrectifier(interfaceindicatedwithadashedlineinFig.1)wereinitiallydesigned,manufacturedandmeasuredsep-arayinordertovalidatetheirperformancepriortothereal-izationofthecompleterectenna.

Ashortedannularring-slotstructure,firstintroducedin[8],wasutilizedasanantennaelement.AntennafeedwascomposedofatransmissionlineTL1andtwoquarter-wavetransformers

ManuscriptreceivedJune5,2003;revisedOctober28,2003.

TheauthorsarewiththeTampereUniversityofTechnology,InstituteofElec-tronics,FIN-33101Tampere,Finland(:jouko.heikkinen@tut.fi).

DigitalObjectIdentifier10.1109/LMWC.2004.827114

TL2andTL3.Antennawasdesignedfor50inputimpedanceformeasurementpurposes.Themeanslotradius

waspreliminarilydesignedsothattheslotwavelength[9]atthedesiredcenterfrequency5.8GHzwasequaltothemeanslotcircumference

(1)

SuchastructurewassimulatedusingMOM(MethodofMo-ments)sothattheinputimpedancewascalculatedattheouteredgeoftheslot(atofTL1).Itwasfoundoutthat(1)predictedthevicinityoftheantennasfirstresonantfrequencyatreasonableaccuracy,butthefrequencyfortheoptimumCPradiationwasabout1.4timeshigher.Thatwasmainlybecause

(1)doesnotincludetheeffectofthering-slotfeed.Meanslotradius,slotwidth andshortanglewerethereforevariedinsimulationstofindtheminimumaxialratioat5.8GHz.AllsimulationswereperformedwithADS(AdvancedDesignSystem)Momentumusingstripmetallizationlayers.Finaldi-mensionsoftheantennaarelistedinTableI.

RectifierwascomposedofamicrowaveSchottkydetectordiodepairD,abypasscapacitorC,aloadresistorRandachokeinductorL.Thediodepair(HSMS-2862)wasconnectedinashunt-seriesmanner(so-calledvoltagedoublercircuit)inordertolowertheinputimpedanceandizetheoutputdcvoltage.Theinputimpedanceoftherectifiercircuitwastrans-formedinto50withtransmissionlinesTL4andTL5andtwosymmetricalsectionsofanopenStub.Rectifierwasde-signedwithADSEM/Circuitco-simulationfeatureusingstripmetallizationlayers.ComponentvaluesanddimensionsofthematchingelementsaregiveninTableI.

RESULTS

Separateantennaandrectifieraswellasthecompleterectennaweremanufacturedbywetetching.Measuredandsimulatedinputreturnlossoftheantennaandtherectifier(inputpower5dBm)areshowninFig.2.Theoreticalandexperimentalresultsagreedfairlywellandaquitegoodimpedancematchwasachievedinthevicinityof5.8GHz.Thedifferencebetweensimulatedandmeasuredresultswasmainlyduetomanufacturingtolerancesandanerrorduetotheconnectorusedinmeasurements.

AntennaperformanceforCPradiationwastestedinanane-choicchamber.Alineargainof4dBandanaxialratioof2dBweremeasured.ACPgaincorrespondingtotheseresultswastherefore6.1dB[10].Performancewasquitesimilarwitha

5.2GHzantennadesignedonanearlythreetimesthickerrigidlaminate[7].Itshouldbealsonotedthattheproposedantenna

1531-1309/04$20.00?2004IEEE

HEIKKINENANDKIVIKOSKI:LOW-PROFILECIRCULARLYPOLARIZEDRECTIFYINGANTENNA 163

Fig.1.Rectennalayout(topviewandcrosssection).

TABLEI

DimensionsandComponentValuesfortheRectennaShowninFig.1

Fig.2.Measuredandsimulatedreturnlossoftheantennaandtherectifier.Antenna,measured;antenna,simulated; rectifier,measured; rectifier,simulated.

isbidirectional,thatistheradiationpatternsarenearlyidenticalonbothsidestheantennane(xy-neinFig.1).

Theperformanceoftherectifierwasmeasuredatpowerlevelsof5dBmand0dBm.Theinputoftherectifierwasconnectedtoamicrowavesignalgeneratorandtheoutputanddcvoltage(Vout)wasmeasured.Fromtheseresultstheconver-sionefficiencywascalculated.ResultsarerepresentedinFig.3.Comparedtotheresultsreportedin[7],ahigheroutputvoltagewasachievedmainlyduetoahigherload.However,lowerconversionefficiencywasdetectedasaresultofreducedcurrentthroughthediodepair.

Fig.3.Measuredrectifieroutputdcvoltage(Vout)andefficiency(Eff)attwodifferentinputpower(Pin)levels. Vout@Pin=5dBm;Vout@Pin=0dBm; E@Pin=5dBm;E@Pin=

0dBm.

Thecompleterectennawasmeasuredinananechoicchamber.Astandardgainhornantenna(gain20dB)wasusedasatransmitter.Therectennawasrotated360in45stepsinthexy-neandtheoutputvoltagewasmeasuredateachposition.Measurementswereperformedat1mand2mdistancebetweentheantennas.Thetransmittedpowerwas26dBmat1mand32dBmat2m.ResultsforoutputvoltageandaxialratioareshowninFig.4.At5.8GHz,outputvoltageof1.1Vand1.3Vandaxialratioof2.1dBand1.5dBwasmeasuredat1mand2mdistances,respectively.Theumoutputwasmeasuredat5.85GHz,apectedbasedonFig.2.

164 IEEEMICROWAVEANDWIRELESSCOMPONENTSLETTERS,VOL.14,NO.4,APRIL2004

Fig.4.Measuredrectennaoutputdcvoltage(Vout)andaxialratioattwodifferenttransmissiondistancesandtransmittedpowerlevels(Pt).Distance=

1m,Pt=26dBm; outputdcvoltage; axialratio;Distance=

2m,Pt=32dBm; outputdcvoltage;axialratio.

Theaxialratiosat1mand2mdistancesarenotidenticalbecausethemeasuredrectennawasinthenear-fieldregionofthetransmitntenna,wheretheradiationpropertiesvarywithdistance.Thefar-fielddistanceofthetransmitntennaat

5.8GHzwas2.4m.

Conclusions

Acircularlypolarizedrectennaformicrowavewirelesspowertransmissionat5.8GHzwasmanufacturedonathinlow-lossmicrowavelaminate.Basedonthetestresults,thechosenlow-profileandflexiblelaminateiswellsuitedforthisdesign.Theproposedrectifyingantennashouldbeusefulasa“virtualbat-tery”inapplicationswherethereceiverisrotatingrelativetothetransmitter.Theuseofthinandflexiblelaminateinsteadof

thickandrigidenablesmountingintoslightlycurvedsurfacesandreducestheweightoftherectenna.Themeasuredrectenna,havinganaxialratioof1.5dB,producedanoutputvoltageof

1.3Vovera2mdistancewhen32dBmmicrowavepowerwastransmitted.Comparedtoapreviousdesign,theperformancewasbetterintermsofhigheroutputvoltagewhereassomede-teriorationinaxialratioandconversionefficiencywasnoticed.

References

R.Bridgelall,“Characterizationof patibleblue-tooth/802.11RFIDtags,”RFDesign,vol.25,no.7,pp.34–46,July2002.

X.M.QingandY.W.M.Chia,“Circularlypolarizedcircularringslotantennafedbystriplinehybridcoupler,”Electron.Lett.,vol.35,no.25,

pp.2154–2155,Dec.1999.

K.-L.Wong,C.-C.Huang,andW.-S.Chen,“Printedringslotantennaforcircularpolarization,”IEEETrans.AntennasPropagat.,vol.50,pp.75–77,Jan.2002.

M.K.FriesandR.Vahldieck,“Uninarcircularlypolarizedslot-ringantennaarchitectures,”RadioSci.,vol.38,