电子信息工程专业英语翻译清华出版社

TechnicalEnglish,ForInformationScienceandElectronicEngineering,Unit3,EMFields,AntennaandMicrowaves,PartI,ElectromagneticField,3,NewWords,4,1,Theelectromagneticfieldisaphysicalfieldproducedbyelectricallychargedobjects.Itaffectsthebehaviorofchargedobjectsinthevicinityofthefield.Theelectromagneticfieldextendsindefinitelythroughoutspaceanddescribestheelectromagneticinteraction.Itisoneofthefourfundamentalforcesinthenature(theothersaregravitation,theweakinteraction,andthestronginteraction),电磁场在空间无限延伸，并描述电磁相互作用。,5,2,Thefieldcanbeviewedasthecombinationofanelectricfieldandamagneticfield.Theelectricfieldisproducedbystationarycharges,andthemagneticfieldbymovingcharges(currents);thesetwoareoftendescribedasthesourcesofthefield.ThewayinwhichchargesandcurrentsinteractwiththeelectromagneticfieldisdescribedbyMaxwellsequationsandtheLorentzforcelaw.,电荷和电流与电磁场相互作用的方式由麦克斯韦方程组和洛伦兹力定律所描述。,6,3,Fromaclassicalpointofview,theelectromagneticfieldcanberegardedasasmooth,continuousfield,propagatedinawavelikemanner,whereasfromaquantummechanicalpointofview,thefieldcanbeviewedasbeingcomposedofphotons.,从经典的角度，电磁场可认为是光滑、连续的场，以波动方式传播；而从量子力学的角度，场可看作是由光子组成的。,7,4Structureoftheelectromagneticfield,Theelectromagneticfieldmaybeviewedintwodistinctways.Continuousstructure:Classically,electricandmagneticfieldsarethoughtofasbeingproducedbysmoothmotionsofchargedobjects.Forexample,oscillatingchargesproduceelectricandmagneticfieldsthatmaybeviewedina“smooth”,continuous,wavelikemanner.,例如，振荡电荷产生电场和磁场，可看成平滑的、连续的波动方式。,8,5,Inthiscase,energyisviewedasbeingtransferredcontinuouslythroughtheelectromagneticfieldbetweenanytwolocations.Forinstance,themetalatomsinaradiotransmitterappeartotransferenergycontinuously.Thisviewisusefultoacertainextent(radiationoflowfrequency),butproblemsarefoundathighfrequencies(seeultravioletcatastrophe).Thisproblemleadstoanotherview.,Theultravioletcatastrophe,alsocalledtheRayleigh-Jeanscatastrophe,wasapredictionofearly20thcenturyclassicalphysicsthatanidealblackbodyatthermalequilibriumwillemitradiationwithinfinitepower.,9,6,Discretestructure:Theelectromagneticfieldmaybethoughtofinamore“coarse”way.Experimentsrevealthatelectromagneticenergytransferisbetterdescribedasbeingcarriedawayinphotonswithafixedfrequency.PlancksrelationlinkstheenergyEofaphotontoitsfrequencynthroughtheequation:E=hn,普朗克的关系式将光子的能量E及其频率n通过下式联系起来,10,6,wherehisPlancksconstant,namedinhonorofMaxPlanck,andnisthefrequencyofthephoton.Forexample,inthephotoelectriceffecttheemissionofelectronsfrommetallicsurfacesbyelectromagneticradiationitisfoundthatincreasingtheintensityoftheincidentradiationhasnoeffect,andthatonlythefrequencyoftheradiationisrelevantinejectingelectrons.1,例如在光电效应中，即因电磁辐射而从金属表面发射电子的现象，我们发现增加入射辐射的强度并无影响，只有辐射频率与发射的电子有关。,11,7,Thisquantumpictureoftheelectromagneticfieldhasprovedverysuccessful,givingrisetoquantumelectrodynamics,aquantumfieldtheorydescribingtheinteractionofelectromagneticradiationwithchargedmatter.,已经证明电磁场的量子描述是非常成功的，引出了量子电动力学，一种描述电磁辐射与带电物体之间的相互作用的量子场理论。,12,8Dynamicsoftheelectromagneticfield,Inthepast,electricallychargedobjectswerethoughttoproducetwotypesoffieldassociatedwiththeirchargeproperty.Anelectricfieldisproducedwhenthechargeisstationarywithrespecttoanobservermeasuringthepropertiesofthechargeandamagneticfield(aswellasanelectricfield)isproducedwhenthechargemoves(creatinganelectriccurrent)withrespecttothisobserver.,相对于测量电荷性质的观察者，电荷静止时产生电场，电荷运动（产生电流）时产生磁场（和电场）。,13,8,Overtime,itwasrealizedthattheelectricandmagneticfieldsarebetterthoughtofastwopartsofagreaterwholetheelectromagneticfield.2,随着时间的推移，人们认识到电场和磁场是电磁场这一整体的两个部分。,14,9,Oncethiselectromagneticfieldhasbeenproducedfromagivenchargedistribution,otherchargedobjectsinthisfieldwillexperienceaforce(inasimilarwaythatplanetsexperienceaforceinthegravitationalfieldoftheSun).Iftheseotherchargesandcurrentsarecomparableinsizetothesourcesproducingtheaboveelectromagneticfield,thenanewnetelectromagneticfieldwillbeproduced.3,电磁场中其它带电体就会受到一个力的作用,如果另外这些电荷和电流的大小与产生上述电磁场的源是可比的，那么将产生一个新的净电磁场。,15,9,Thus,theelectromagneticfieldmaybeviewedasadynamicentitythatcausesotherchargesandcurrentstomove,andwhichisalsoaffectedbythem.TheseinteractionsaredescribedbyMaxwellsequationsandtheLorentzforcelaw.,电磁场可以认为是一个动力学实体，它促使其它电荷和电流运动，同时又受它们影响。,PartII,MicrostripAntenna,17,NewWords,18,NewWords,19,1,Intelecommunication,thereareseveraltypesofmicrostripantennas(alsoknownasprintedantennas)themostcommonofwhichisthemicrostrippatchantennaorpatchantenna.Apatchantennaisanarrowband,wide-beamantennafabricatedbyetchingtheantennaelementpatterninmetaltracebondedtoaninsulatingdielectricsubstratewithacontinuousmetallayerbondedtotheoppositesideofthesubstratewhichformsagroundplane.1,片状天线是一种窄带宽波束的天线，通过将天线单元图样蚀刻到粘贴在绝缘基底上的金属轨迹而制成，基底的另一面则粘贴连续的金属层形成接地平面。,20,1,Commonmicrostripantennaradiatorshapesaresquare,rectangular,circularandelliptical,butanycontinuousshapeispossible.Somepatchantennaseschewadielectricsubstrateandsuspendametalpatchinairaboveagroundplaneusingdielectricspacers;theresultingstructureislessrobustbutprovidesbetterbandwidth.,一些片状天线为了避免绝缘基底，在接地平面的上空用绝缘逆电流器悬挂一个金属贴片；这种结构的鲁棒性不是很好，但能提供更好的带宽。,21,1,Becausesuchantennashaveaverylowprofile,aremechanicallyruggedandcanbeconformable,theyareoftenmountedontheexteriorofaircraftandspacecraft,orareincorporatedintomobileradiocommunicationsdevices.2,因为这种天线外形低矮，机械强度大，并且形状上适应性强，通常装在飞机或太空飞行器外表，或组合在移动无线电通信设备上。,22,2,Microstripantennasarealsorelativelyinexpensivetomanufactureanddesignbecauseofthesimple2-dimensionalphysicalgeometry.TheyareusuallyemployedatUHFandhigherfrequenciesbecausethesizeoftheantennaisdirectlytiedtothewavelengthattheresonantfrequency.Asinglepatchantennaprovidesamaximumdirectivegainofaround6-9dBi.,因为其简单的二维形状,dBi:decibelisotropic,theforwardgainofanantennacomparedwiththeisotropicantenna,whichuniformlydistributesenergyinalldirections.,23,2,Itisrelativelyeasytoprintanarrayofpatchesonasingle(large)substrateusinglithographictechniques.Patcharrayscanprovidemuchhighergainsthanasinglepatchatlittleadditionalcost;matchingandphaseadjustmentcanbeperformedwithprintedmicrostripfeedstructures,againinthesameoperationsthatformtheradiatingpatches.,通过平板印刷技术我们很容易在单个大绝缘体上印刷贴片阵列。,用形成辐射电波的片状微带天线的同样机理，可对印刷微带天线的馈电结构进行匹配和相位调节。,24,2,Theabilitytocreatehighgainarraysinalow-profileantennaisonereasonthatpatcharraysarecommononairplanesandinothermilitaryapplications.,以低矮的天线构成高增益阵列的能力是片状天线广泛用于飞机和其他军事应用的原因之一。,25,3,Themostcommonlyemployedmicrostripantennaisarectangularpatch.Therectangularpatchantennaisapproximatelyaone-halfwavelengthlongsectionofrectangularmicrostriptransmissionline.Whenairistheantennasubstrate,thelengthoftherectangularmicrostripantennaisapproximatelyone-halfofafree-spacewavelength.,矩形贴片天线长近似为矩形微带传输线的一段，其长度等于半波长。,矩形微带天线的长度大约为自由空间波长的一半,26,3,Sincetheantennaisloadedwithadielectricasitssubstrate,thelengthoftheantennadecreasesastherelativedielectricconstantofthesubstrateincreases.Theresonantlengthoftheantennaisslightlyshorterbecauseoftheextendedelectric“fringingfields”whichincreasetheelectricallengthoftheantennaslightly.,天线的谐振长度略短一些，这是因为边缘场稍微增加了天线的电气长度。,Fringingfields:theelectricfieldsproducedbyscatteredelectronsinanelectronmicroscope.,27,3,Anearlymodelofthemicrostripantennaisasectionofmicrostriptransmissionlinewithequivalentloadsoneitherendtorepresenttheradiationloss.,微带天线的一个早期模型是一段微带传输线，在一端具有等效负载，代表辐射损耗。,28,4,Thedielectricloadingofamicrostripantennaaffectsbothitsradiationpatternandimpedancebandwidth.Asthedielectricconstantofthesubstrateincreases,theantennabandwidthdecreaseswhichincreasestheQfactoroftheantennaandthereforedecreasestheimpedancebandwidth.3,随着基底介电常数的增大，天线的带宽减小，其Q值提高，因而阻抗带宽减小。,29,4,Thisrelationshipdidnotimmediatelyfollowwhenusingthetransmissionlinemodeloftheantenna,butisapparentwhenusingthecavitymodelwhichwasintroducedinthelate1970s.Theradiationfromarectangularmicrostripantennamaybeunderstoodasapairofequivalentslots.,当使用天线的传输线模型时这种情况并没有发生，到了七十年代后期出现空腔模型时这种情况就显现出来了。,30,4,Theseslotsactasanarrayandhavethehighestdirectivitywhentheantennahasanairdielectricanddecreasesastheantennaisloadedbymaterialwithincreasingrelativedielectricconstant.,这些狭缝就像一个阵列，当天线使用空气电介质时方向性最好，但是当天线的负载材料的相对介电常数增加时方向性会减弱。,31,5,Anadvantageinherenttopatchantennasistheabilitytohavepolarizationdiversity.Patchantennascaneasilybedesignedtohavevariouspolarizations,usingmultiplefeedpoints,orasinglefeedpointwithasymmetricpatchstructures.4Thisuniquepropertyallowspatchantennastobeusedinmanytypesofcommunicationslinksthatmayhavevariedrequirements.,片状天线能很容易地通过多个馈点或具有非对称片结构的单一馈点设计成具有各种极化特性。,32,6,Thehalf-waverectangularmicrostripantennahasavirtualshortingplanealongitscenter.Thismaybereplacedwithaphysicalshoringplanetocreateaquarter-wavelengthmicrostripantenna.Thisissometimescalledahalf-patch.,沿中心的虚拟短路平面,用物理短路平面替代上述虚拟短路平面就可以做成四分之一波长微带天线,33,6,Theantennaonlyhasasingleradiationedge(equivalentslot)whichlowersthedirectivity/gainoftheantenna.Theimpedancebandwidthisslightlylowerthanahalf-wavelengthfullpatchasthecouplingbetweenradiatingedgeshasbeeneliminated.,由于没有辐射边缘之间的耦合，所以阻抗带宽比半波长全贴片窄。,PartIII,Microwaves,35,NewWords,36,NewWords,37,1,Microwavesareelectromagneticwaveswithwavelengthslongerthanthoseofterahertz(THz)frequencies,butrelativelyshortforradiowaves.Microwaveshavewavelengthsapproximatelyintherangeof30cm(frequency=1GHz)to1mm(300GHz).Thisrangeofwavelengthshasledmanytoquestionthenamingconventionusedformicrowavesasthenamesuggestsamicrometerwavelength.1,这个波长范围已经使人对命名习惯提出了问题，因为微波使人联想到微米波长。,38,1,However,theboundariesbetweenfarinfraredlight,terahertzradiation,microwaves,andultra-high-frequencyradiowavesarefairlyarbitraryandareusedvariouslybetweendifferentfieldsofstudy.Thesameequationsofelectromagnetictheoryapplyatallfrequencies.,是相当随意的，在不同的学科领域有不同的用法,39,1,Apparatusandtechniquesmaybedescribedas“microwave”whenthewavelengthsofsignalsareroughlythesameasthedimensionsoftheequipment,sothatlumped-elementcircuittheoryisnolongeraccurate.,信号的波长与设备的尺度大致相同,集总元件电路理论不再准确,40,1,Thetermmicrowavegenerallyrefersto“alternatingcurrentsignalswithfrequenciesbetween300MHz(3108Hz)and300GHz(31011Hz).”However,bothIECstandard60050andIEEEstandard100define“microwave”frequenciesstartingat1GHz(30cmwavelength).,41,2,Theexistenceofelectromagneticwaves,ofwhichmicrowavesarepartofthefrequencyspectrum,waspredictedbyJamesClerkMaxwellin1864fromhisequations.In1888,HeinrichHertzwasthefirsttodemonstratetheexistenceofelectromagneticwavesbybuildinganapparatusthatproducedanddetectedmicrowavesintheUHFregion.,构建了在UHF频段产生和检测微波的装置，证明电磁波的存在,42,2,3,In1894J.C.Bosepubliclydemonstratedradiocontrolofabellusingmillimeterwavelengths,andconductedresearchintothepropagationofmicrowaves.Themicrowaverangeincludesultra-highfrequency(UHF)(0.33GHz),superhighfrequency(SHF)(330GHz),andextremelyhighfrequency(EHF)(30300GHz)signals.,微波传播的研究,43,4,Above300GHz,theabsorptionofelectromagneticradiationbyEarthsatmosphereissogreatthatitiseffectivelyopaque,untiltheatmospherebecomestransparentagainintheso-calledinfraredandopticalwindowfrequencyranges.,地球大气对高于300GHz的电磁辐射的吸收是如此之大，以至于变得实际上是不透明，直到所谓的红外线和可见光窗口的频率范围，大气又变得透明。,44,5Devices,Vacuumtubebaseddevicesoperateontheballisticmotionofelectronsinavacuumundertheinfluenceofcontrollingelectricormagneticfields,andincludethemagnetron,klystron,travelingwavetube(TWT),andgyrotron.2,基于电子管的器件是在受控制电场和磁场影响的真空内由电子的冲击运动而工作的，包括磁控管，速调管，行波管和振动陀螺仪。,45,5,Thesedevicesworkinthedensitymodulatedmode,ratherthanthecurrentmodulatedmode.Thismeansthattheyworkonthebasisofclumpsofelectronsflyingballisticallythroughthem,ratherthanusingacontinuousstream.3,这意味着它们是基于真空管发出的电子簇工作的，而不是用连续的电子流。,46,6Uses,Amicrowaveovenworksbypassingmicrowaveradiation,usuallyatafrequencyof2450MHz(awavelengthof12.24cm),throughthefood.Water,fat,andsugarmoleculesinthefoodabsorbenergyfromthemicrowavebeaminaprocesscalleddielectricheating.,47,6,Manymolecules(suchasthoseofwater)areelectricdipoles,meaningthattheyhaveapositivechargeatoneendandanegativechargeattheother,andthereforerotateastheytrytoalignthemselveswiththealternatingelectricfieldinducedbythemicrowavebeam.,它们一端带正电，另一端带负电,它们力图与微波波束所引起的交变电场保持一致,48,6,Thismolecularmovementcreatesheatastherotatingmoleculeshitothermoleculesandputthemintomotion.Microwaveheatingismostefficientonliquidwater,andmuchlesssoonfatsandsugars(whichhavelessmoleculardipolemoment),andfrozenwater(wherethemoleculesarenotfreetorotate).,旋转分子撞击其它分子，使他们运动，这种分子运动产生热量。,微波加热对液态水是最有效的，其次为脂肪和糖类（分子偶极矩较少）以及冷冻水（分子不能自由转动）。,49,6,Microwaveheatingissometimesincorrectlyexplainedasarotationalresonanceofwatermolecules:suchresonanceonlyoccursatmuchhigherfrequencies,inthetensofgigahertz.Moreover,largeindustrial/commercialmicrowaveovensoperatinginthe900MHzrangealsoheatwaterandfoodperfectlywell.,微波加热有时被错误地解释为水分子的旋转共振，而这种共振只能发生在数十千兆赫的高频。,此外，大型工业/商业微波炉在900兆赫范围内工作，也能很好地加热水和食物。,50,7,Acommonmisconceptionisthatmicrowaveovenscookfoodfromthe“insideout”.Inreality,microwavesareabsorbedintheouterlayersoffoodinamannersomewhatsimilartoheatfromothermethods.Theraysfromamicrowaveelectricallymanipulatewaterparticlestocookfood.,实际上与其它加热方法类似，微波被食物外层吸收。,51,7,Itisactuallythefrictioncausedbythemovementthatcreatesheatandwarmsthefood.Themisconceptionarisesbecausemicrowavespenetratedrynonconductivesubstancesatthesurfacesofmanycommonfoods,andthusoftendepositinitialheatmoredeeplythanothermethods.,这种误解源自微波在许多普通食物的表面穿透干燥的非导电物质，因此比起其它方法来能在更深层堆积初始热量。,52,7,Dependingonwatercontentthedepthofinitialheatdepositionmaybeseveralcentimetersormorewithmicrowaveovens,incontrasttobroiling,whichreliesoninfraredradiation,orthethermalconvectionofaconvectionoven,whichdepositheatshallowlyatthefoodsurface.,使用微波炉，初始热沉积的深度可达几个公分以上，这取决于水分含量的多少,而焙烤是依赖红外辐射或烤箱内的热对流，它们在食物表面存储的热量很浅。,53,7,Depthofpenetrationofmicrowavesisdependentonfoodcompositionandthefrequency,withlowermicrowavefrequenciesbeingmorepenetrating.,54,8,Microwaveradioisusedinbroadcastingandtelecommunicationtransmissionsbecause,duetotheirshortwavelength,highlydirectiveantennasaresmallerandthereforemorepracticalthantheywouldbeatlongerwavelengths(lowerfrequencies).,微波无线电用于广播和电信传输，这是因为其波长短，与波长较长时相比，方向性天线体积更小也更实用。,55,8,Thereisalsomorebandwidthinthemicrowavespectrumthanintherestoftheradiospectrum;theusablebandwidthbelow300MHzislessthan300MHzwhilemanyGHzcanbeusedabove300MHz.Typically,microwavesareusedintelevisionnewstotransmitasignalfromaremotelocationtoatelevisionstationfromaspeciallyequippedvan.,比起其它无线电波段，微波频谱有更宽的频带可以利用，频率低于300兆赫时可用带宽小于300兆赫，而在300兆赫以上可用频带达到几个GHz。,56,9,Beforetheadventoffiberoptictransmission,mostlongdistancetelephonecallswerecarriedviamicrowavepoint-to-pointlinksthroughsitesliketheAT&TLongLinesfacility.Startingintheearly1950s,frequencydivisionmultiplexwasusedtosendupto5,400telephonechannelsoneachmicrowaveradiochannel,withasmanyastenradiochannelscombinedintooneantennaforthehoptothenextsite,upto70kmaway.4,20世纪50年代开始，人们用频分复用在每一个微波无线电信道中传送多达5400路电话，将10路无线电信道组合起来送到一个天线，发送到70公里以外的下一个中继站。,57,10,Radaralsousesmicrowaveradiationtodetecttherange,speed,andothercharacteristicsofremoteobjects.,58,11,WirelessLANprotocols,suchasBluetoothandtheIEEE802.11specifications,alsousemicrowavesinthe2.4GHzISMband,although802.11ausesISMbandandUNIIfrequenciesinthe5GHzrange.Licensedlong-range(uptoabout25km)WirelessInternetAccessservicescanbefoundinmanycountries(butnottheUSA)inthe3.54.0GHzrange.,经授权许可的远距离无线互联网接入业务,ISMbands:industrial,scientificandmedicalradiobands.UNII:UnlicensedNationalInformationInfrastructure,59,12,MetropolitanAreaNetworks:MANprotocols,suchasWiMAX(WorldwideInteroperabilityforMicrowaveAccess)basedintheIEEE802.16specification.TheIEEE802.16specificationwasdesignedtooperatebetween2to11GHz.