Systems Aspects of Millimeter-Wave

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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