RFMicrowave Low Noise OscillatorsWord下载.docx
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Lownoiseoscillatorsoperatingfrom1MHzto10GHzhavebeenbuiltwhichuseInductorCapacitor(LC),crystal,SurfaceAcousticWave(SAW),Dielectric,HelicalandTransmissionLineResonators.Theseoscillatorsdemonstratenoiseperformanceusuallywithin1dBofthepredictedminimum.MMIClownoiseoscillatorshavebeendesignedandfabricated.Tunablelownoiseoscillators(bothhybridandMMIC)havebeenbuiltandareunderfurtherinvestigation.Nonlinearmodellingtechniques,usingVolterraSeries,havebeendevelopedwhichaccuratelypredicttheoutputpowerandtheoperatingfrequency.Ultra-lownoisereferencestandardsforoperationupto20GHzarebeingdevelopedusingsapphiredielectricresonators.Presentperformanceat7.5GHzexceeds-143dBc/Hz@10kHzoffset.Improvementsofaround35dBarecurrentlyunderinvestigation.Newtechniqueshavejustbeendeveloped(Sept.2000seepublications,patentapplicationsandbookbelow)whichsuppresstheflickernoiseby20dBdowntothethermallimitsforoffsetsabove10kHz.
Thephasenoiseresultsarenowwithin1/2dBofthetheoreticalminimumnoiseperformancesetbythermalnoise.
Thisisachievedbyusingfeedforwardamplifiersastheoscillatorsustainingstageandincorporatingthelimitingelsewhere.
SupportedbyEPSRC
Phasenoiseinoscillators:
NoisepowerversusQL/QOfromtheory(solidcurve)andexperiment(pointsx).
FlickerNoiseMeasurementandReduction
JKAEverard,PDallas
FlickernoisecausesconsiderabledegradationtotheperformanceofoscillatorsanddividerswhichuseGaAs.AsystemformeasuringthelowfrequencyFlickernoiseonthegateanddrainofaGaAsFETandtheAMandPMcomponentsthattheseFlickernoisestransposeontoacarrierhasbeendevelopedasshownbelow.Thissystemhasbeenusedtomeasurethecrosscorrelationbetweenthelowfrequencyandthedemodulatedhighfrequencynoisesbymeasuringallthecomponentssimultaneouslyonadigitizingoscilloscope.ThesemeasurementscanbeusedtodeterminetheFlickernoisesourcesinGaAsFETsandthecorrelationbetweenthem.FlickernoisereductiontechniquesinGaAsFEToscillatorsarebeinginvestigated.TransposedGainOscillatorsoffer-143dBc/Hz@10kHzoffsetat7.5GHz.Newtechniqueshavejustbeendeveloped(Sept.2000seepublications,patentapplicationsandbookbelow)whichsuppresstheflickernoiseby20dBdowntothethermallimitsforoffsetsabove10kHz.
Thisisachievedbyusingfeedforwardamplifiersastheoscillatorsustainingstageandincorporatingthelimitingelsewhere.Lowfrequencyfeedbackforflickernoisesuppressionisnowbeingre-investigatedandoptimised.
Noisemeasurementsystem.TypicalcrosscorrelationbetweendrainnoiseandAMcomponent
TunableResonatorsandLowLossFilters
JKAEverard
Newdesigntechniqueshavebeenappliedtomicrowavebandpassfilterstodemonstratecompactlowcostfiltersusingtransmissionlines,helicalresonatorsandcapacitors.Striplinefilterstructureswhichdemonstrateverylowradiationlosshavebeendevelopedasshown.ThesefiltersdonotrequirescreeningboxesandhavetheinherenthighQsofthematerialsused.UnloadedQsof520havebeenobtainedat5GHzinunscreenedfilters.Newresonators(bothhybridandMMIC)whichcantuneoveranearoctavefrequencyrangehavebeendevelopedforuseintunablemicrowaveoscillatorsandfilters.NewhighQ(235at2GHz)verycompactresonatorsandfiltershavebeendeveloped.
UltrahighQresonatorsoperatingatroomtemperaturearecurrentlyunderinvestigation.RoomtemperatureQsof24,000and60,000arereadilyachievedwithsimplestructuresusingBaTiO3andSapphirerespectively.
Newstructureswitha10foldimprovementinQ(atroomtemperature)arecurrentlybeingmodelledandinvestigated.
Lowloss4.5GHzbandpassfilter.
Frequencyresponse(insertionloss)ofunscreenedbandpassfilter.
BroadbandPowerEfficientRFandMicrowaveAmplifiers
BroadbandpowerefficientClassEamplifiershavebeendevelopedforusefrom120to180MHz.NewCADtechniquesweredevelopedtoimplementtherapiddesignandevaluationofsuchcircuits.Newcircuitswhichpresenttheoptimumcompleximpedancetotheactivedeviceoverabroadfrequencyrangehavebeendeveloped.Thesedesigntechniquesarenowbeingextendedtoproducehybrid,microstripandMMICversionsoperatingabove900MHzforuseinmobiletelephonesandcommunicationssystems.Distributedloadnetworkshavebeendevelopedwhichproduceefficienciesgreaterthan75%with500mWoutputpowerat1GHz.A'
realtime'
loadnetworksimulatorhasbeenwrittenwhichallowsfulltuningofthecomponentvaluesandfrequencywhileobservingthewaveformsatallthenodesin'
onanoscilloscopelikedisplay.
MicrowaveBroadbandNegativeGroupDelayCircuits
CBroomfield,JKAEverard
Microwavenegativegroupdelaycircuitsofferingoctavebandwidthshaverecentlybeenproduced-seeElectronicslettersNovember2000,Vol.36,No33.
DynamicSelfRoutingAllOpticalSwitches
JKAEverard,MPage-Jones
AllopticalSwitcheshavebeendevelopedwhichautomaticallyrouteopticaldatasignalswherethedata,destinationaddressandopticalpowerareallcontainedwithinthesingleopticallaserbeam.ThisistheopticalequivalentoftheoldStrowgerExchange.AnewallopticalsystemwithoneinputandthreeoutputshasrecentlybeendemonstratedattheRoyalSocietyusinganinputopticalpowerof300micro-watts.Thisisbelievedtobethefirstallopticalswitchwhichcontainsthedata,destinationaddressandpowerallwithinthesame300microwattI/Plaserbeam.
Theswitchoperatesbyautomaticallyproducingadiffractiongratingwithinannonlinearcrystalwhichrotatesaccordingtothedestinationaddress.
Thecodingiscarriedwithintheautocorrelationoftheinputsignalwhichinthiscaseisthedistancebetweenadjacentpulses.
Allopticalswitching.
DemonstrationofswitchingbetweenO/P1O/P2
PicosecondOpto-Electronics
JKAEverard,NGhogomu
Ultra-fastopto-electronicdetectorsandmixershavebeendevelopedwithbandwidthsextendingfromDCto50GHz(5psrisetime).Mostrecentlya3-waveopto-electronicmixerhasbeendemonstratedwhichdetectstwoopticalsignalsspaced33GHzapart.Thesesignalsaredetectedanddownconvertedto500MHzallwithinthesamedevice.MMICversions,asillustratedbelow,havebeenfabricatedandshowntowork.Analysispredictsperformanceoftenbetterthanidealphotodiodes.Thesedevicesarebeingusedforcoherentdetectionanddownconversionandasphasedetectorsforphaselockingsemiconductorlasers.Currentdevicesdemonstrateasensistivityof-60dBm@33GHzina1MHzbandwidthwithaS/N=1.ShotNoiselimitedsubpicoseconddevicesarecurrentlybeinginvestigated.
33GHz3-waveopto-electronicmixer.
OpticalFibreSpectrumAnalysers
JKA.Everard,MPage-Jones
AnopticalfibrespectrumanalyserhasbeenbuiltwhichusesaMichelsonfibreinterferometertomeasuretheautocorrelationfunctionandhencethespectrumofopticalsignals.Theautocorrelationfunctionisobtainedbyusingthestretchingofpolarisationmaintainingfibreinabalancedconfiguration.Differentialdelaysof3cmsinascantimeof50mshavebeenachieved.TechniquesforjoiningAndrewssinglemodeellipticallycoredfibretoDfibrewithtransmissiongreaterthan80%havebeendeveloped.Thisallowedallfibresystemstobebuilt.Thesesystemscanalsobeusedforfibresensorsandforprogrammingtheallopticalself-routingswitches
OpticalFibreSensors
JKAEverard,NGhogomi,RThomas,MPage-Jones
Microwaveradartechniques(SpreadSpectrumRamanOTDR)havebeenusedtodevelopadistributedopticalfibretemperaturesensorcapableofmeasuringthetemperaturedistributionoveraKilometreoffibrewithdegreesensitivityandmetrespatialresolutionasshownbelow.CoherentBrillouintemperaturesensorshavebeendemonstratedandareunderfurtherinvestigation.Newsensorswithsubmeterresolutionarebeingdeveloped.
SupportedbyEPSRCandUniversityofYork
Measurementoftemperatureover1kmusinganopticalfibresensor.
MMICImplementationsofOpto-ElectronicandMicrowaveCircuits
Oscillators,tunableresonators,filters,highefficiencyamplifiersandphotoconductivethreewaveopticalmixersanddetectorshavebeenbuiltonhybridandmonolithicmicrowaveintegratedcircuits(MMIC'
s).Currentlycompleteradiotransmitters(includingthepowerefficientRFamplifier)andreceiversarebeingdesignedonmonolithicmicrowaveintegratedcircuitsandhavealreadybeenbuiltinhybridform.AmicrowaveDopplerRadarisshownbelow.Coherentopticalreceiversanddownconvertersincorporatingthemicrowaveoscillatorsarebeingdesigned.
MicrowaveDopplerRadar.
FutureProjects
RFandMicrowaves:
UltraLowNoiseTunableReferenceOscillatorswithPhaseNoise~-180dBcat10kHzoffsetatXband
BroadTuningLowNoiseVCOs
HighlyPowerEfficientLow