Introductiontoradiowaves
Atypeofelectromagneticwaves.Electromagneticwaveswithafrequencybelow30,000,000KHz(300GHz)orwithawavelengthgreaterthan1mmarecalledradiowavesbecausetheyaregeneratedbythealternatingcurrentoftheoscillatingcircuitandcanbeemittedandabsorbedbytheantenna.
Electromagneticwavesincludemanytypes,arrangedintheorderoffrequencyfromlowtohigh:radiowaves,infraredrays,visiblelight,ultravioletrays,X-raysandgammarays.Radiowavesaredistributedinthefrequencyrangebelow300GHz.
Radiowavesindifferentbandshavedifferentpropagationcharacteristics.
Thelowerthefrequency,thesmallerthepropagationloss,thelongerthecoveragedistance,andthestrongerthediffractionability.However,thefrequencyresourcesofthelowfrequencybandaretight,andthesystemcapacityislimited.Therefore,theradiowavesofthelowfrequencybandaremainlyusedinsystemssuchasbroadcasting,television,andpaging.
Thehighfrequencybandisrichinfrequencyresourcesandthesystemcapacityislarge.Butthehigherthefrequency,thegreaterthepropagationloss,thecloserthecoveragedistance,andtheweakerthediffractionability.Inaddition,thehigherthefrequency,thegreaterthetechnicaldifficultyandthecorrespondingincreaseinthecostofthesystem.
Whenthemobilecommunicationsystemselectsthefrequencybandtobeused,comprehensiveconsiderationshouldbegiventothecoverageeffectandcapacity.Comparedwithotherfrequencybands,UHFfrequencybandhasabettercompromisebetweencoverageeffectandcapacity,soitiswidelyusedinthemobilecommunicationfieldofterminalssuchasmobilephones.Ofcourse,aspeople’sdemandsformobilecommunicationsareincreasingandtherequiredcapacityisincreasing,mobilecommunicationssystemswillinevitablydeveloptowardshighfrequencybands.
Thespeedofradiowavesonlychangeswiththeelectricalandmagneticpropertiesofthepropagationmedium.Thespeedofradiowavespropagatinginvacuumisequaltothespeedoflightpropagatinginvacuum,becauseradiowavesandlightarebothelectromagneticwaves.ThespeedatwhichradiowavespropagateinothermediaisVε=C/sqrt(ε).Whereεisthedielectricconstantofthepropagationmedium.Thedielectricconstantofairisveryclosetothatofvacuum,slightlygreaterthan1,sothepropagationspeedofradiowavesintheairisslightlylessthanthespeedoflight,usuallyweapproximateittobeequaltothespeedoflight.
Radiowavepropagation
Thewayofradiowavepropagation
Forfreespace,becausethereisnoblockinfreespace,radiowavepropagationisonlydirect,andtherearenootherphenomena..
Fortheactualpropagationenvironmentindailylife,duetotheexistenceofvariousobjectsontheground,thepropagationofradiowavesincludesdirectradiation,reflection,diffraction(diffraction),etc.Inaddition,forindoorortrainForusers,partofthesignalcomesfromthepenetrationofradiowavesintobuildings.Allofthesehavecausedthediversityandcomplexityofradiowavepropagation,andhaveincreasedthedifficultyofresearchonradiowavepropagation.
Directradiation
Directradiationwithinthelineofsightcanbeseenasradiowavespropagatinginfreespace.Thedirectwavepropagationlossformulaisthesameasthepathlossformulainfreespace:PL=32.44+20lgf+20lgd.Amongthem,PListhepathlossinfreespace,andtheunitisdB.Fisthefrequencyofthecarrier,inMHz.disthedistancebetweenthetransmittingsourceandthereceivingpoint,theunitiskm.
Reflection,RefractionandPenetration
Whenanobstacleisencounteredduringthepropagationofelectromagneticwaves,whenthesizeoftheobstacleismuchlargerthanthewavelengthoftheelectromagneticwave,Electromagneticwaveswillbereflectedandrefractedatthejunctionofdifferentmedia.Inaddition,themediapropertiesofobstacleswillalsoaffectreflections.Foragoodconductor,reflectiondoesnotcauseattenuation;foraninsulator,itonlyreflectsapartoftheincidentenergy,andtherestisrefractedintothenewmediumtocontinuetopropagate;fornon-idealmedium,electromagneticwavespenetratethemedium,thatis,whenthemediumpenetrates,themediumWillabsorbtheenergyofelectromagneticwavesandproducepenetratingfading.Thepenetrationlossisnotonlyrelatedtothefrequencyoftheelectromagneticwave,butalsorelatedtothematerialandsizeofthepenetratingobject.
Generally,indoorradiowavesignalsarethesuperpositionofthepenetrationcomponentandthediffractioncomponent,andthediffractioncomponentaccountsforthemajority.Therefore,ingeneral,theindoorandoutdoorleveldifferenceofhigh-frequencysignals(suchas1800MHz)islargerthanthatoflow-frequencysignals(800MHz).Moreover,afterthelowfrequencysignalenterstheroom,duetothepoorerpenetrationability,thefieldstrengthdistributionismoreuniformaftervariousreflectionsintheroom;andafterthehighfrequencysignalenterstheroom,partofthepenetrationisagainpenetrated,andtheindoorsignaldistributionisnotIfitistoouniform,theuserwillfeelthatthesignalfluctuatesgreatly.
Diffraction(diffraction)
Whenanobstacleisencounteredduringthepropagationofelectromagneticwaves,whenthesizeoftheobstacleisclosetothewavelengthoftheelectromagneticwave,theelectromagneticwavecanDiffractedfromtheedgeoftheobject.Diffractioncanhelpcovershadowareas.
Scattering
Intheprocessofelectromagneticwavepropagation,obstaclesareencountered.Thesizeoftheobstaclesissmallerthanthewavelengthofelectromagneticwaves,andsuchobstaclesperunitvolumeWhenthenumberisverylarge,scatteringwilloccur.Scatteringoccursonthesurfaceofroughobjects,smallobjects,orotherirregularobjects,suchasleaves,streetsigns,andlampposts.
Radiowavepropagationatdifferentdistances
Line-of-sightpropagation
Thegeneralformofline-of-sightradiowavepropagationismainlydirectwavesSuperimpositionwiththegroundreflectedwavemayresultinastrongersignalorweakersignal.
Becausetheearthissphericalandaffectedbytheradiusofcurvatureoftheearth,thereisalimitdistanceRmaxforline-of-sightpropagation,whichisaffectedbytheheightofthetransmittingantenna,theheightofthereceivingantennaandtheradiusoftheearth.
Non-line-of-sightpropagation
Thegeneralformsofnon-line-of-sightpropagationofradiowavesare:diffractedwaves,reflectedwavesinthetroposphereandreflectedwavesintheionosphere.
①Diffractedwaves
Diffractedwavesarethemainsourceofsignalsinsidebuildingsorshadowareas.Theintensityofthediffractedwaveisgreatlyaffectedbythepropagationenvironment,andthehigherthefrequency,theweakerthediffractedsignal.
②Thetroposphericreflectionwave
Thetroposphericreflectionwaveisgeneratedinthetroposphere.Thetroposphereisaheterogeneousmedium,whichchangeswithtimeduetoweatherconditions.Itsreflectioncoefficientdecreaseswithincreasingheight.Thisslowlychangingreflectioncoefficientbendstheelectricwave.Thetroposphericreflectionmethodisusedinwirelesscommunicationswithawavelengthlessthan10meters(thatis,afrequencygreaterthan30MHz).Reflectedwavesinthetroposphereareextremelyrandom.
③Ionosphericreflectionwave
Whenthewavelengthisgreaterthan1meter(thatis,thefrequencyislessthan300MHz),theionosphereisareflector.Theelectricwavesreflectedfromtheionospheremayhaveoneormorejumps,sothiskindofpropagationisusedforlong-distancecommunication.Likethetroposphere,theionospherehasthecharacteristicsofcontinuousfluctuations.
Characteristicsofradiowavesinlandmobilecommunicationenvironment
Complexityofpropagationenvironment
DuetothecomparisonofantennaheightsofmobileterminalsLow,thepropagationpathisalwaysaffectedbytheterrainandman-madeenvironment,causingalargeamountofscattering,reflectionorsuperpositionofthereceivedsignal.
Thecomplexityofthepropagationenvironmentisreflectedinthediversityofterrain,man-madebuildings,andman-madeinterference.Forexample,inaterrainwithwoodsaround,leaveswillcausealotofradiowavestoscatter.Asfortheurbanenvironment,thewaveguideeffectcausedbythetallbuildingsonbothsidesofthestreetincreasesthesignalalongthepropagationdirectiononthestreetandweakensthesignalperpendiculartothepropagationdirection.Thedifferencebetweenthetwoisabout10dB.Inaddition,theignitionofmotorvehicles,powerlines,industryandotherhumaninfluenceswillcauseinterferencetothereceivedsignal.
Randommobilityofmobileterminals
Mobileterminalsarealwaysmoving.Evenifthemobileterminaldoesnotmove,thesurroundingenvironmentisalwayschanging,suchaspeople,Themovementofvehicles,thewindblowingleaves,etc.,makethepropagationpathbetweenthebasestationandthemobileterminalconstantlychange.Inaddition,changesinthemovingdirectionandmovingspeedofthemobileterminalrelativetothebasestationwillcausechangesinthesignallevel,whichcanonlybedescribedbytheprobabilitydistributionofarandomprocess.
Theopennessofpropagation
Theopennessoftheradiowavepropagationspaceleadstoseriousspaceinterference.Themorecommononesareco-channelinterference,adjacentchannelinterference,andintermodulationinterference.Asthefrequencyreusefactorincreases,co-adjacentfrequencyinterferencewillbecomethemaininterference.
Propagationclassification
Radiowavesfromthelaunchingsitetothereceivingsitemainlyincludeskywaves,groundwaves,andspacelinearwaves.Thecharacteristicsofeachwaveareasfollows:
Groundwave:Theelectricwavepropagatingalongthesurfaceoftheearth,calledgroundwave.Duringthepropagationprocess,theelectricwaveisabsorbedbytheground,sothepropagationdistanceisnotfar.Thehigherthefrequency,thegreaterthegroundabsorption,sowhenshortwaveandultrashortwavespropagatealongtheground,thedistanceisrelativelyclose,generallynomorethan100kilometers,whilethemediumwavepropagationdistanceisrelativelylong.Theadvantageisthatitislessaffectedbytheclimate,thesignalisstable,andthecommunicationreliabilityishigh.
Skywave:Theradiowavepropagatedbythereflectionoftheionosphereintheatmosphere,calledskywave,orionosphericreflectionwave.Thetransmittedradiowavesarereflectedbytheionospheremorethan70-80kilometersfromthegroundtothereceivinglocation,andtheirpropagationdistanceisrelativelylong,generallymorethan1,000kilometers.Thedisadvantageisthatitisgreatlyaffectedbytheionosphericclimateandthepropagationsignalisveryunstable.Theshort-wavefrequencybandisthebestfrequencybandforsky-wavepropagation.Theshort-wavesingle-sidebandradiostationsequippedbyfishingvesselsareequipmentthatusessky-wavepropagationforlong-distancecommunication.
Spacelinearwave:Aradiowavethatpropagatesinastraightlinefromthelaunchingsitetothereceivingsiteinspace,calledthespatiallinearradiowave,alsoknownasthelinearwaveorline-of-sightwave.Thepropagationdistanceistheline-of-sightrange,whichisonlytensofkilometers.Thewalkie-talkiesandradarsequippedwithfishingvesselsareallequipmentthatusesspacewavepropagationtocommunicate.
Transversewaves
Radiowavesaretransversewaves.Thatis,thedirectionoftheelectricfieldandthemagneticfieldareperpendiculartothedirectionofwavepropagation.Whenradiowavespropagateinspace,theymustbeaffectedbytheatmosphere,especiallytheionospherehasthemostsignificantinfluence,causingradiowavestoberefractedandattenuated.Amongthem,thegreaterthewavelength,Thegreatertherefractionandattenuation.
Accordingtothedifferentpropagationcharacteristicsofradiowavewavelengths,differentcommunicationservicesusedifferentbands.Forexample,longwavesareusedfornavigationandfixedservices;mediumandshortwavesareusedformobileservices;microwavesareusedforradioastronomyandspacecommunications.
Radiowavecharacteristics
Thefadingcharacteristicsofradiowaves
Thefadingofradiowavesduringpropagationisaveryimportantcharacteristic.Itisdescribedinthreescales:mediumandsmall.
Largescaleisusedtodescribethemediansignal(areaaverage).Ithasapowerlawpropagationcharacteristic,thatis,themediansignalpowerisinverselyproportionaltoacertainpoweroftheincreaseindistancelength.
Mesoscaleisusedtodescribeslowfading.Itistheaveragepowerchangesuperimposedonthemedianlevelofthelarge-scalepropagationcharacteristics.Whenexpressedindecibels,thischangetendstobenormallydistributed.
Smallscalesareusedtodescribefastfading.ItusuallyobeystheRayleighprobabilitydensityfunction,alsoknownasRayleighfading.
Dopplerfrequencyshift
AccordingtotheDopplereffect,duetotherelativemovementbetweentheradiowavetransmitterandreceiver,thefrequencyofthesignalreceivedbythereceiverwillbethesameasthefrequencyofthesignalreceivedbythetransmitter.Thereisadifferencebetweenthetransmittedsignalfrequencies,andthisdifferenceistheDopplershift.
Dopplerfrequencyshiftconformstothefollowingformula:
isthesynthesizedfrequency
istheworkingfrequency
isthemaximumDopplerfrequency
visthemaximumspeedofthemobileterminal
isthewavelength
istheanglebetweenthepropagationdirectionofthemultipathsignalandthetraveldirectionofthemobileterminal
timedispersionsumEqualization
Timedispersionoriginatesfromreflection,andthereflectedsignalcomesfromanobjectseveralkilometersawayfromthereceivingantenna.Forexample,thebasestationcontinuouslysendsasequenceof"1"and"0".Ifthetimefortheremotereflectedsignaltoreachthemobileterminalisjustonebitbehindthedirectsignal,thereceivingterminalwilldetect"0"fromthedirectsignal,andatthesametime"1"isdetectedinthereflectedsignal,whichcausesinter-symbolinterference,whichiscalledtimedispersion.Usingadaptiveequalizationtechnologycanreducetheimpactoftimedispersion.
Thehistoryofradiowaves
Maxwellfirstclarifiedthetheoreticalbasisofelectromagneticwavepropagationinhispaper"DynamicTheoryofElectromagneticFields"submittedtotheRoyalSociety.Hisworkwascompletedbetween1861and1865.
HeinrichRudolfHertzfirstverifiedMaxwell'stheorythroughexperimentsbetween1886and1888.Waveequation.
OnChristmasEvein1906,ReginaldFessendenusedtheheterodynemethodtoachievethefirstradiobroadcastinhistoryinMassachusetts,USA.FanXindabroadcastedhisownviolinperformanceof"ChristmasEve"andrecitationofthe"Bible".TheMarconiResearchCenterinChelmsford,England,startedbroadcastingtheworld'sfirstregularradioentertainmentprogramin1922.
HeinrichRudolfHertzfirstverifiedMaxwell'stheorythroughexperimentsbetween1886and1888.Heprovedthatradioradiationhasallthecharacteristicsofwaves,andfoundthattheelectromagneticfieldequationscanbeexpressedbypartialdifferentialequations,usuallycalledwaveequations.
In1893,NikolaTeslapubliclydemonstratedradiocommunicationforthefirsttimeinSt.Louis,Missouri,USA.Inreportsforthe"FranklinCollegeofPhiladelphia"andthe"NationalElectricLightAssociation",hedescribedanddemonstratedthebasicprinciplesofradiocommunication.Theinstrumenthemadecontainsallthebasicelementsoftheradiosystembeforetheinventionofthetube.
Marconi(GuglielmoMarconi)hasapatentthatisgenerallyconsideredtobetheworld'sfirstradiotechnology,BritishPatentNo.12039,"Improvementofelectricalpulseandsignaltransmissiontechnologyandrequiredequipment".
NikolaTeslaobtainedapatentforradiotechnologyintheUnitedStatesin1897.In1898,Marconiopenedtheworld'sfirstradiofactoryinHallStreet,Chelmsford,England,employingabout50people.However,theUSPatentOfficerevokeditspatentin1904andinsteadgrantedMarconiapatentfortheinventionofradio.ThismovemaybetheresultofMarconi’seconomicbackingfiguresintheUnitedStates,includingEdisonandAndrewCarnegie.In1909,MarconiandKarlFerdinandBraunwontheNobelPrizeinPhysicsfor"thecontributionoftheinventionofwirelesstelegraphy."
In1943,shortlyafterTesla'sdeath,theU.S.SupremeCourtreaffirmedthatTesla'spatentwasvalid.ThisdecisionrecognizesthathisinventionwascompletedbeforeMarconi'spatent.Somepeoplethinkthatthisdecisionwasobviouslymadeforeconomicreasons.Inthisway,theUSgovernmentinWorldWarIIcouldavoidpayingMarconi'spatentroyalties.
Radiowaveapplication
Radiowasfirstusedinnavigation,usingMorsetelegraphtotransmitinformationbetweenshipandland.Nowadays,radiohasavarietyofapplications,includingwirelessdatanetworks,variousmobilecommunications,andradiobroadcasting.
Thefollowingaresomeofthemainapplicationsofradiotechnology:
Navigation
Theearliestformofbroadcastingisnauticalradiotelegraph.Itusesaswitchtocontrolwhetherthecontinuouswaveistransmittedornot,andthesignalgeneratedatthereceiverisMorsecode.
*AMbroadcastingcanbroadcastradiosignals.Amplitudemodulationbroadcastingusesamplitudemodulationtechnology,thatis,thegreaterthereceivedintensity,thegreatertheenergyemittedbytheradiostation.Suchsignalsaresusceptibletointerferencefromsourcessuchaslightningorotherinterferencesources.*FMbroadcastingcanbroadcastradiosignalswithhigherfidelitythanAMbroadcasting.Forfrequencymodulation,thelargerthebandwidth,thehigherthefrequencyofthetransmittedsignal.FMbroadcastingworksinVeryHighFrequency(VHF).Thehigherthefrequencyband,thelargerthefrequencybandwidthithas,whichcanaccommodatemoreradiostations.Atthesametime,thepropagationofradiowaveswithshorterwavelengthsisclosertothestraight-linepropagationcharacteristicsoflightwaves.
*ThesidebandsofFMbroadcastingcanbeusedtospreaddigitalsignalssuchasstationlogos,programnameprofiles,websiteaddresses,stockmarketinformation,etc.Insomecountries,afterbeingmovedtoanewarea,theFMradiocanautomaticallyfindtheoriginalchannelbasedonthesidebandinformation.
*RadiostationsusedinnavigationandaviationuseVHFamplitudemodulationtechnology.Thisallowslightantennastobeusedonairplanesandships.
*Government,fire,policeandcommercialradiostationsusuallyusenarrowbandFMtechnologyondedicatedfrequencybands.Theseapplicationsusuallyuseabandwidthof5KHz.ComparedwiththebandwidthofFMradioortelevision,fidelityhastobesacrificed.
*Civilormilitaryhigh-frequencyservicesuseshortwavesforcommunicationbetweenships,aircraft,orisolatedlocations.Inmostcases,single-sidebandtechnologyisused,whichsaveshalfofthefrequencybandcomparedtoamplitudemodulationtechnology,andusesthetransmitpowermoreeffectively.
*TerrestialTrunkedRadio(TETRA)isadigitaltrunkingtelephonesystemdesignedforspecialdepartmentssuchasthemilitary,police,andemergencyservices.
*Amateurradioisaradiostationcommunicationinvolvingradioenthusiasts.Amateurradiostationscanusemanyopenfrequencybandsontheentirespectrum.Hobbyistsusedifferentformsofcodingmethodsandtechniques.Somelatercommercialtechnologies,suchasfrequencymodulation,single-sidebandamplitudemodulation,digitalpacketradioandsatellitesignaltransponders,werefirstappliedbyamateurs.
Calling
*Cellularphonesormobilephonesarecurrentlythemostcommonlyusedwirelesscommunicationmethods.Cellularphonecoverageareasareusuallydividedintomultiplecells.Eachcelliscoveredbyabasestationtransmitter.Theoretically,theshapeofthecellisahoneycombhexagon,whichisalsothesourceofthenameofthecellphone.Currentlywidelyusedmobilephonesystemstandardsinclude:GSM,CDMAandTDMA.Afewoperatorshavealreadybeguntoprovidenext-generation3Gmobilecommunicationservices,andtheirleadingstandardsareUMTSandCDMA2000.
*Therearetwoformsofsatellitephone:INMARSATandIridiumsatellitesystem.Bothsystemsprovideglobalcoverageservices.INMARSATusesgeostationarysatellitesandrequiresadirectionalhigh-gainantenna.Iridiumisalow-orbitsatellitesystemthatdirectlyusesmobilephoneantennas
Video
*TheusualanalogTVsignalusesamplitudemodulation,frequencymodulationandsynthesisoftheimagetopropagateinthesamesignal.
*DigitalTVusesMPEG-2imagecompressiontechnology,whichrequiresonlyabouthalfthebandwidthofanalogTVsignals.
Emergencyservices
*Emergencypositionindicatingradiobeacons(EPIRBs),emergencypositioningtransmittersorpersonalpositioningbeaconsareusedtoaddresspeopleinemergencysituationsOrmeasuresmallradiotransmittersthatarepositionedviasatellites.Itsfunctionistoproviderescuerswiththepreciselocationofthetargetinordertoprovidetimelyrescue.
Datatransmission
*Digitalmicrowavetransmissionequipment,satellites,etc.usuallyuseQuadratureAmplitudeModulation(QAM).TheQAMmodulationmethodusesboththeamplitudeandphaseofthesignaltoloadinformation.Inthisway,alargeramountofdatacanbetransferredonthesamebandwidth.
*IEEE802.11isthecurrentwirelessLANstandard.Itusesthe2GHzor5GHzfrequencyband,andthedatatransmissionrateis11Mbpsor54Mbps.
Navigation
*Activeandpassiveradiodevicescanbeusedtoidentifyandindicatetheidentityofobjects.
*Allsatellitenavigationsystemsusesatellitesequippedwithpreciseclocks.Thenavigationsatellitebroadcastsitspositionandtiminginformation.Thereceiverreceivessignalsfrommultiplenavigationsatellitesatthesametime.Thereceiverobtainsitsdistancetoeachsatellitebymeasuringthepropagationtimeoftheradiowave,andthencalculatesitspreciseposition.
*TheLoransystemalsousesthepropagationtimeofradiowavesforpositioning,butitstransmittersarealllocatedonland.
*TheVORsystemisusuallyusedforflightpositioning.Itusestwotransmitters,onedirectionaltransmitteralwaysemitsandrotatesatafixedratelikeabeacon'sspotlight.Whenthepointingtransmitterisfacingnorth,anotheromnidirectionaltransmitterwillemitpulses.TheaircraftcanreceivesignalsfromtwoVORstationsanddetermineitspositionbycalculatingtheintersectionofthetwobeams.
*Radioorientationistheearliestformofradionavigation.Radioorientationusesamovableloopantennatofindthedirectionofthestation.
Radar
*Radarcalculatesthetarget'sdistancebymeasuringthedelayofreflectedradiowaves.Andthesurfacetypeofthetargetissensedbythepolarizationandfrequencyofthereflectedwave.
*Navigationradarusesultrashortwavetoscanthetargetarea.Thegeneralscanningfrequencyistwotofourtimesperminute,andtheterrainisdeterminedbyreflectedwaves.Thistechnologyiscommonlyusedinmerchantshipsandlong-distancecommercialaircraft.*Multipurposeradarusuallyusesthefrequencybandofnavigationradar.However,theemittedpulsesaremodulatedandpolarizedinordertodeterminethesurfacetypeofthereflector.Anexcellentmulti-purposeradarcandistinguishheavyrain,land,vehicles,etc.
*Thesearchradarusesshort-wavepulsestoscanthetargetarea,usually2-4timesperminute.SomesearchradarsusetheDopplereffecttodistinguishmovingobjectsfromthebackground
*Thehomingradarusesasimilarprincipletothesearchradar,butitcanscanasmallareaquicklyandrepeatedly.Uptoseveraltimespersecond.
*Weatherradarissimilartosearchradar,butusescircularlypolarizedwavesandwavelengthsthatareeasilyreflectedbywaterdroplets.SomeweatherradarsalsousetheDopplereffecttomeasurewindspeed.
Heating
*Themicrowaveovenuseshigh-powermicrowavestoheatfood.(Note:Acommonmisunderstandingisthatthefrequencyusedbymicrowaveovensistheresonancefrequencyofwatermolecules.Infact,thefrequencyusedisaboutone-tenthoftheresonancefrequencyofwatermolecules.)
Power
*Radiowavescangenerateweakelectrostaticandmagneticforces.Undermicrogravityconditions,thiscanbeusedtofixthepositionofobjects.
*Aerospacepower:Thereisaproposaltousethepressuregeneratedbyhigh-intensitymicrowaveradiationasthepoweroftheinterstellarprobe.
Astronomy
*Itistheradiowavesignalemittedbythecosmicbodyreceivedbytheradiotelescopetostudythephysicalandchemicalpropertiesofthecelestialbody.Thissubjectiscalledradioastronomy.