資源描述：
《the rf in rfid passive uhf rfid in practice》由會員上傳分享，免費在線閱讀，更多相關(guān)內(nèi)容在工程資料-天天文庫。
1、CHAPTER2HistoryandPracticeofRFID2.1ItAllStartedwithIFFBythe1930s,theprimitivebiplanesoffabricandwoodthathadpopulatedtheskiesabovethebattle?eldsofWorldWarIhadbecomeall-metalmonoplanescapableofcarryingthousandsofkilogramsofexplosivesandtravelingathundredsofkilometersper
2、hour:bythetimeobser-verscouldvisuallyidentifyanincoming?ight,itwastoolatetorespond.Detectionofair-planesbeyondvisualrangewasthetaskofmicrowaveradar,alsounderrapiddevelopmentinthe30s,butmeredetectionofthepresenceofaircraftbeggedthekeyquestion:whosesideweretheyon?Itwase
3、xactlythisinabilitytoidentifyaircraftthatenabledthemistakenassign-mentofincomingJapaneseaircrafttoanunrelatedUnitedStatesbomber?ightandsoensuredsurpriseatPearlHarborin1941.TheproblemofidentifyingaswellasdetectingpotentiallyhostileaircraftchallengedallcombatantsduringW
4、orldWarII.TheLuftwaffe,theGermanairforce,solvedthisprobleminitiallyusinganingeniouslysimplemaneuver1.DuringengagementswithGermanpilotsatthebeginningofthewar,theBritishnotedthatsquadronsof?ghterswouldsuddenlyandsimultaneouslyexecutearollfornoappa-rentreason.Thiscurious
5、behaviorwaseventuallycorrelatedwiththeinterceptionofradiosignalsfromtheground.ItbecameapparentthattheLuftwaffepilots,whentheyreceivedindicationthattheywerebeingilluminatedbytheirradar,wouldrollinordertochangethebackscatteredsignalre?ectedfromtheirairplanes(Figure2.1).
6、TheconsequentmodulationoftheblipsontheradarscreenallowedtheGermanradaroperatorstoidentifytheseblipsasfriendlytargets.Thisisthe?rstknownexample(atleasttotheauthor)oftheuseofapassivebackscatterradiolinkforidenti?cation,amajortopicoftheremainderofthisbook.Passiverefersto
7、thelackofaradiotransmitterontheobjectbeingidenti?ed;thesignalusedtocommunicateisaradiosignaltransmittedbytheradarstationandscatteredbacktoitbytheobjecttobeidenti?ed(inthiscaseanairplane).1Unfortunately,atthemomentthisisanunveri?edInternetreport,forwhichIhavebeenunable
8、to?ndanarchivalsource—butitissuchafunstoryIhadtoincludeitanyway!Anauthoritativecitationfor(ordebunkingof)thestorywouldbeappr
