ITU-R-P.341-5-无线链路中传输损耗的概念

ITU-RP.341-5无线链路中传输损耗的概念1RECOMMENDATIONITU-RP.341-5*THECONCEPTOFTRANSMISSIONLOSSFORRADIOLINKS**(1959-1982-1986-1994-1995-1999)Rec.ITU-RP.341-5TheITURadiocommunicationAssembly,consideringa)thatinaradiolinkbetweenatransmitterandareceiver,theratiobetweenthepowersuppliedbythetransmitterandthepoweravailableatthereceiverinputdependsonseveralfactorssuchasthelossesintheantennasorinthetransmissionfeedlines,theattenuationduetothepropagationmechanisms,thelossesduetofaultyadjustmentoftheimpedancesorpolarization,etc.;b)thatitisdesirabletostandardizetheterminologyandnotationsemployedtocharacterizetransmissionlossanditscomponents;c)thatRecommendationITU-RP.525providesthefree-spacereferenceconditionsforpropagation,recommendsthat,todescribethecharacteristicsofaradiolinkinvolvingatransmitter,areceiver,theirantennas,theassociatedcircuitsandthepropagationmedium,thefollowingterms,definitionsandnotationsshouldbeemployed:1Totalloss(ofaradiolink)***(symbols:LlorAl)Theratio,usuallyexpressedindecibels,betweenthepowersuppliedbythetransmitterofaradiolinkandthepowersuppliedtothecorrespondingreceiverinrealinstallation,propagationandoperationalconditions.NOTE1–Itisnecessarytospecifyineachcasethepointsatwhichthepowersuppliedbythetransmitterandthepowersuppliedtothereceiveraredetermined,forexample:–beforeoraftertheradio-frequencyfiltersormultiplexersthatmaybeemployedatthesendingorthereceivingend;–attheinputorattheoutputofthetransmittingandreceivingantennafeedlines.2Systemloss(symbols:LsorAs)Theratio,usuallyexpressedindecibels,foraradiolink,oftheradio-frequencypowerinputtotheterminalsofthetransmittingantennaandtheresultantradio-frequencysignalpoweravailableattheterminalsofthereceivingantenna.NOTE1–Theavailablepoweristhemaximumrealpowerwhichasourcecandelivertoaload,i.e.,thepowerwhichwouldbedeliveredtotheloadiftheimpedanceswereconjugatelymatched.NOTE2–Thesystemlossmaybeexpressedby:Ls10log(pt/pa)=Pt–PadB(1)where:pt:radio-frequencypowerinputtotheterminalsofthetransmittingantennapa:resultantradio-frequencysignalpoweravailableattheterminalsofthereceivingantenna._______________*ThisRecommendationshouldbebroughttotheattentionoftheCoordinationCommitteeforVocabulary(CCV).**ThroughoutthisRecommendation,capitallettersareusedtodenotetheratios(dB)ofthecorrespondingquantitiesdesignatedwithlower-casetype,e.g.Pt10logpt.Ptistheinputpowertothetransmittingantenna(dB)relativeto1Wwhenptistheinputpower(W).***AgraphicaldepictionofthisandsubsequentdefinitionsisshowninFig.1.2Rec.ITU-RP.341-5NOTE3–Thesystemlossexcludeslossesinfeederlinesbutincludesalllossesinradio-frequencycircuitsassociatedwiththeantenna,suchasgroundlosses,dielectriclosses,antennaloadingcoillosses,andterminatingresistorlosses.0341-01Lb=Lbf+LmLbfLs=L+Ltc+Lrc=Pt?PaL=Lb?Gt?GrGtGrLtcLrcFIGURE1GraphicaldepictionoftermsusedinthetransmissionlossconceptFree-spacebasictransmissionloss,LbfBasictransmissionloss,LbPropagationmedium,etc.ReceiverFilters,feeder,etc.TransmittingantennalossesIsotropicantennaIsotropicantennaTransmissionloss,LTransmitterFilters,feeder,etc.ReceivingantennalossesReceivingantennaTransmittingantennaSystemloss,LsTotalloss,Ll(referencepointsshouldbespecified)FIGURE.1[0341-01]3Transmissionloss(ofaradiolink)(symbols:LorA)Theratio,usuallyexpressedindecibels,foraradiolinkbetweenthepowerradiatedbythetransmittingantennaandthepowerthatwouldbeavailableatthereceivingantennaoutputiftherewerenolossintheradio-frequencycircuits,assumingthattheantennaradiationdiagramsareretained.NOTE1–Thetransmissionlossmaybeexpressedby:L=Ls–Ltc–LrcdB(2)ITU-RP.341-5无线链路中传输损耗的概念3whereLtcandLrcarethelosses,expressedindecibels,inthetransmittingandreceivingantennascircuitsrespectively,excludingthedissipationassociatedwiththeantennasradiation,i.e.,thedefinitionsofLtcandLrcare10log(r'/r),wherer'istheresistivecomponentoftheantennacircuitandristheradiationresistance.NOTE2–Transmissionlossisequaltosystemlossminusthelossintheradio-frequencycircuitsassociatedwiththeantennas.4Basictransmissionloss(ofaradiolink)(symbols:LborAi)Thetransmissionlossthatwouldoccuriftheantennaswerereplacedbyisotropicantennaswiththesamepolarizationastherealantennas,thepropagationpathbeingretained,buttheeffectsofobstaclesclosetotheantennasbeingdisregarded.LbLGtGrdB(3)whereGtandGrarethedirectivitygains(seeAnnex1)ofthetransmittingandreceivingantennas,respectively,inthedirectionofpropagation.NOTE1–Thebasictransmissionlossisequaltotheratiooftheequivalentisotropicallyradiatedpowerofthetransmittersystemtothepoweravailablefromanisotropicreceivingantenna.NOTE2–Theeffectofthelocalgroundclosetotheantennaisincludedincomputingtheantennagain,butnotinthebasictransmissionloss.5Free-spacebasictransmissionloss(symbols:LbforA0)Thetransmissionlossthatwouldoccuriftheantennaswerereplacedbyisotropicantennaslocatedinaperfectlydielectric,homogeneous,isotropicandunlimitedenvironment,thedistancebetweentheantennasbeingretained(seeRecommendationITU-RP.525).NOTE1–Ifthedistancedbetweentheantennasismuchgreaterthanthewavelength,thefree-spaceattenuationindecibelswillbe:Lbf20log