the rf in rfid passive uhf rfid in practice

《the rf in rfid passive uhf rfid in practice》由会员上传分享，免费在线阅读，更多相关内容在工程资料-天天文库。

1、CHAPTER2HistoryandPracticeofRFID2.1ItAllStartedwithIFFBythe1930s,theprimitivebiplanesoffabricandwoodthathadpopulatedtheskiesabovethebattlefieldsofWorldWarIhadbecomeall-metalmonoplanescapableofcarryingthousandsofkilogramsofexplosivesandtravelingathundredsofkilometersper

2、hour:bythetimeobser-verscouldvisuallyidentifyanincomingflight,itwastoolatetorespond.Detectionofair-planesbeyondvisualrangewasthetaskofmicrowaveradar,alsounderrapiddevelopmentinthe30s,butmeredetectionofthepresenceofaircraftbeggedthekeyquestion:whosesideweretheyon?Itwase

3、xactlythisinabilitytoidentifyaircraftthatenabledthemistakenassign-mentofincomingJapaneseaircrafttoanunrelatedUnitedStatesbomberflightandsoensuredsurpriseatPearlHarborin1941.TheproblemofidentifyingaswellasdetectingpotentiallyhostileaircraftchallengedallcombatantsduringW

4、orldWarII.TheLuftwaffe,theGermanairforce,solvedthisprobleminitiallyusinganingeniouslysimplemaneuver1.DuringengagementswithGermanpilotsatthebeginningofthewar,theBritishnotedthatsquadronsoffighterswouldsuddenlyandsimultaneouslyexecutearollfornoappa-rentreason.Thiscurious

5、behaviorwaseventuallycorrelatedwiththeinterceptionofradiosignalsfromtheground.ItbecameapparentthattheLuftwaffepilots,whentheyreceivedindicationthattheywerebeingilluminatedbytheirradar,wouldrollinordertochangethebackscatteredsignalreflectedfromtheirairplanes(Figure2.1).

6、TheconsequentmodulationoftheblipsontheradarscreenallowedtheGermanradaroperatorstoidentifytheseblipsasfriendlytargets.Thisisthefirstknownexample(atleasttotheauthor)oftheuseofapassivebackscatterradiolinkforidentification,amajortopicoftheremainderofthisbook.Passiverefersto

7、thelackofaradiotransmitterontheobjectbeingidentified;thesignalusedtocommunicateisaradiosignaltransmittedbytheradarstationandscatteredbacktoitbytheobjecttobeidentified(inthiscaseanairplane).1Unfortunately,atthemomentthisisanunverifiedInternetreport,forwhichIhavebeenunable

8、tofindanarchivalsource—butitissuchafunstoryIhadtoincludeitanyway!Anauthoritativecitationfor(ordebunkingof)thestorywouldbeappr