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页数:43页
时间:2019-08-08
《Systems Aspects of Millimeter-Wave》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、Chapter2SystemsAspectsofMillimeter-WavePowerAmplifiersTheprimarymotivationforoperatingwirelesssystemsathigherfrequenciesliesinthefactthatanincreaseinfrequencyisgenerallyassociatedwithanincreaseinbandwidthincommunicationsystems,aswellasanimprovementinresolutioninimagingandran
2、gingsystems.Alongsidethesefactors,areductioninthephysicalsizeofcomponentsandantennasalsoaccompaniesallwirelesssystemsthatoperateathigherfrequencies.Asonewouldexpect(andasseveraldecadesofresearchhavemadeabundantlyclear),therearefundamentallychallengingaspectsofmillimeter-wav
3、esystemsthatcomplicatethedesignprocessandhinderthewide-spreadimplementationofsuchsystems.Thecharacteristicsofsemiconductordevicesaresuchthattheperformanceofthedevicedecreaseswithanincreaseinfrequency,andaparticulartechnologytypicallyexhibitslowergain,anincreasednoisefigurean
4、dimpairedlinearityperformanceasfrequencyincreases.Thisreductioninperformancecangenerallybeattributedtotheincreasedlossesthatmaterialsexperienceathigherfrequencies.Moreover,free-spacepropagationofelectromagneticwavesexhibitlossesthatrapidlyincreasewithincreasingfrequency—apa
5、rtfromdistinctwindowsinthefrequencyspectrumwhereattenuationissomewhatreduced,thesewindowsappeararound35,90,140and250GHzinthemillimeter-wavespectrum.Consequently,thebandslistedherearepopularforimplementingwirelesssystemsinthetradi-tionalsense(wheremaximizingrangeisafundament
6、alrequirement).Ontheotherhand,oneoftheoxygenabsorptionbandsexistsat60GHz,whichmeansthatalargeportionofthepowercontainedinanelectromagneticwavewillbeabsorbedbyoxygenmoleculesinfreespace.Whilethisbandisnotatallsuitableforimplementingaconventionalwirelesssystem,giventhesignific
7、antlyreducedpropagationdistance,itisusefulinhigh-densitynetworksandprovidesthebenefitofaggressivefrequencyreuseinarelativelysmallarea.Improvementsinprocessandmanufacturingtechnologyinthelastdecadeorsohavebroughtwiththemanewwaveofresearchfocusedonsystem-on-chip(SoC)solutionsf
8、orcomplexcommercialwirelesssystems.Thisisinstarkcontrast©SpringerInternationalPubl
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