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Microwaveandourlife

Thisarticleisabouttheelectromagneticwave.Forthecookingappliance,seeMicrowaveoven.Forotheruses,seeMicrowaves(disambiguation).

AtelecommunicationstowerwithavarietyofdishantennasformicrowaverelaylinksonFrazierPeak,VenturaCounty,California.

Theatmosphericattenuationofmicrowavesindryairwithaprecipitablewatervaporlevelof0.001mm.Thedownwardspikesinthegraphcorrespondtofrequenciesatwhichmicrowavesareabsorbedmorestrongly.Therighthalfofthisgraphincludesthelowerrangesofinfraredbysomestandards

Microwavesareaformofelectromagneticradiationwithwavelengthsrangingfromaslongasonemetertoasshortasonemillimeter,orequivalently,withfrequenciesbetween300MHz(0.3GHz)and300GHz.[1][2]ThisbroaddefinitionincludesbothUHFandEHF(millimeterwaves),andvarioussourcesusedifferentboundaries.Inallcases,microwaveincludestheentireSHFband(3to30GHz,or10to1cm)atminimum,withRFengineeringoftenrestrictingtherangebetween1and100GHz(300and3mm).

Theprefixmicro-inmicrowaveisnotmeanttosuggestawavelengthinthemicrometerrange.Itindicatesthatmicrowavesaresmallcomparedtowavesusedintypicalradiobroadcasting,inthattheyhaveshorterwavelengths.Theboundariesbetweenfarinfrared,terahertzradiation,microwaves,andultra-high-frequencyradiowavesarefairlyarbitraryandareusedvariouslybetweendifferentfieldsofstudy.

Beginningatabout40GHz,theatmospherebecomeslesstransparenttomicrowaves,dueatlowerfrequenciestoabsorptionfromwatervaporandathigherfrequenciesfromoxygen.Aspectralbandstructurecausesabsorptionpeaksatspecificfrequencies(seegraphatright).Above100GHz,theabsorptionofelectromagneticradiationbyEarth'satmosphereissogreatthatitisineffectopaque,untiltheatmospherebecomestransparentagainintheso-calledinfraredandopticalwindowfrequencyranges.

Thetermmicrowavealsohasamoretechnicalmeaninginelectromagneticsandcircuittheory.Apparatusandtechniquesmaybedescribedqualitativelyasmicrowavewhenthefrequenciesusedarehighenoughthatwavelengthsofsignalsareroughlythesameasthedimensionsoftheequipment,sothatlumped-elementcircuittheoryisinaccurate.Asaconsequence,practicalmicrowavetechniquetendstomoveawayfromthediscreteresistors,capacitors,andinductorsusedwithlower-frequencyradiowaves.Instead,distributedcircuitelementsandtransmission-linetheoryaremoreusefulmethodsfordesignandanalysis.Open-wireandcoaxialtransmissionlinesusedatlowerfrequenciesarereplacedbywaveguidesandstripline,andlumped-elementtunedcircuitsarereplacedbycavityresonatorsorresonantlines.Inturn,atevenhigherfrequencies,wherethewavelengthoftheelectromagneticwavesbecomessmallincomparisontothesizeofthestructuresusedtoprocessthem,microwavetechniquesbecomeinadequate,andthemethodsofopticsareused.