Presenter:MiZhiqiangHunanModernLogisticsCollegeBasicKnowledgeofRFIDAntennaContents1OverviewofRFIDantenna2ConceptanalysisOverviewofRFIDantenna01Theelectronictagandthereaderandwriterconstructanon-contactinformationtransmissionchannelbetweenthemthroughtheirrespectiveantennas,asshowninFigure2-7.WhethertheRFtagorthereaderworksproperly,itisinseparablefromtheantennaorthecouplingcoil:(1)InordertostartthecircuitofpassiveRFtagchip,itisnecessarytoobtainenoughenergythroughtheantennaintheelectromagneticfieldgeneratedbythereaderantenna.(2)Theantennadeterminesthecommunicationchannelandmodebetweentheradiofrequencytagandthereader.Theantennaplaysakeyroleinthedatacommunicationbetweentheradiofrequencytagandthereader.CardortagCardortagCardortagAntennasTheRFIDantennaofshort-rangeapplicationsystemlessthan1mgenerallyadoptsthecoilantennawithsimpletechnologyandlowcost,whichmainlyworksinthemiddleandlowfrequencyband.Forlong-distanceapplicationsover1m,IDantennaswithmicrostrippatchesordipolesareneeded,whichoperateinhighfrequencyandmicrowavebands.InRFdevices,thematchingproblembetweenantennaandtagchipbecomesmoreseriouswhentheoperatingfrequencyincreasestothemicrowavearea.Thegoalofthelineistotransmitthemaximumenergyintoandoutofthelabelchip.Thisrequirescarefuldesignoftheantennaandfreespaceandmatchingofitsattachedtagchips.OverviewofRFIDantenna01Conceptanalysis021.Conceptanalysis:dBm,dBi,dBd,dB,dBc（1）dBmdBmisavalueofabsolutepower,anditsformulais:10lgP(powervalue/1mW).[Example2-1]IfthetransmittingpowerPis1mW,itwillbe0dBmafterconversiontodBm.[Example2-2]For40Wpower,theconvertedvalueperdBmunitshouldbe101g(40W/1mW)=101g(40000)=10lg4+10lg10+101g1000=46dBm.1.Conceptanalysis:dBm,dBi,dBd,dB,dBc（2）dBi

anddBddBianddBdarevaluesofgain(powergain),bothofwhicharerelativevalues,butreferencebenchmarksaredifferent.ThereferencedatumofdBiisomnidirectionalantennaandthatofdBdisdipole,sotheyareslightlydifferent.ItisgenerallybelievedthatthevalueexpressedbydBiis2.15largerthanthatexpressedbydBdforthesamegain.[Example2-3]Foranantennawithagainof16dBd,thegainis18.15dBiwhenconvertedintoaunitdBi(usuallyneglectingdecimaldigits,18dBi).[Example2-4]0dBd=2.15dBi.[Example2-5]TheantennagainofGSM900canbe13dBd(15dBi)andthatofGSM1800canbe15dBd(17dBi).Conceptanalysis021.Conceptanalysis:dBm,dBi,dBd,dB,dBc（3）dBdBistheunitofpowergainandrepresentsarelativevalue.WhencalculatinghowmanydBsthepowerofAislargerorsmallerthanthatofB,theformulathatcanbeusedis:10lg(powerofA/powerofB).[Example2-6]IfthepowerofAistwiceaslargeasthepowerofB,thereis101g(powerofA/powerofB)=10lg2=3dB.Inotherwords,thepowerofAis3dBgreaterthanthepowerofB.[Example2-7]The100mtransmissionlossofthe7/8-inchGSM900feederisabout3.9dB.[Example2-8]IfthepowerofAis46dBmandthepowerofBis40dBm,itcanbesaidthatAis6dBlargerthanB.[Example2-9]Ifthegainoftheantennais12dBdandthegainoftheantennais14dBd,itcanbesaidthatAis2dBsmallerthanB.Conceptanalysis021.Conceptanalysis:dBm,dBi,dBd,dB,dBc（4）dBcdBcisaunitthatrepresentstherelativevalueofpower,exactlythesameasdB.Ingeneral,dBcisrelativetocarrierpower.Inmanycases,itisusedtomeasuretherelativevalueofcarrierpower,suchastomeasureinterference(co-channelinterference,intermodulationinterference,cross-modulationinterference,out-of-bandinterference,etc.)andtherelativevaluesofcoupling,spurs,etc.WheredBcisused,inprinciple,dBcanalsobeusedinstead.Conceptanalysis021.Conceptanalysis:dBm,dBi,dBd,dB,dBc（5）dBmPower/Level(dBm):Theoutputcapabilityoftheamplifier,typicallyinunitsofW,mW,dBm.NotethatdBmistheabsolutepowerlevelindecibelstaking1mWasthereferencevalue.Theconversionformulaisasfollows.Level(dBm)=10lgW5W→10lg5000=37dBm10W→10lg10000=40dBm20W→10lg20000=43dBmItisnotdifficulttoseethatforeverydoublingofpower,thelevelvalueisincreasedby3dBm.Conceptanalysis022.Gain(dB):isthemagnification,theunitcanbeexpressedindecibels(dB).Thatis:dB=10lgA(Aisthepoweramplificationfactor).3.InsertionlossReferstotheincreasedattenuationofadeviceorcomponentafteritisconnectedtothetransmissioncircuit.TheunitisexpressedindB.4.Selectivity:Measurethegainintheworkingfrequencybandandtheabilitytosuppresstheout-of-bandradiation.The-3dBbandwidthisthebandwidthwhenthegainisreducedby3dB,andthesameistruefor-40dBand-60dB.Conceptanalysis025.Third-orderintermodulation:Iftherearetwosinusoidalsignalsω1andω2,manyintermodulationcomponentswillbegeneratedduetononlinearaction,whereintwofrequencycomponentsof2ω1-ω2and2ω2-ω1arecalledthird-orderintermodulationcomponents,andtheirpowerTheratioofthepowerofP3tothesignalω1orω2iscalledthethird-orderintermodulationcoefficientM3.Thatis,M3=10lgP3/P1(dBc)6.Noisefigure:Generallydefinedastheratiooftheoutputsignal-to-noiseratiototheinputsignal-to-noiseratio,theactualuseisconvertedtodecibels.TheunitisindB.7.Couplingdegree:Thepowerratioofthecoupledporttotheinputport,indB.8.Isolation:Theratioofthepowerofthelocaloscillatororsignalleakingtootherportstotheoriginalpower,indB.Conceptanalysis029.Antennagain(dB):referstotheabilityoftheantennatoconcentratethetransmittedpowerinaspecifieddirection.Generally,thefieldstrengthEobtainedbymaximizingtheradiationdirectionoftheantennaiscomparedwiththeuniformfieldstrengthE0oftheidealisotropicantenna,andthegainisincreasedbyamultipleofthepowerdensity.Ga=E2/E0210.Antennapattern:Itisthe