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1、INTENSITYANGLEOFARRIVALEFFECTSONMICROWAVEPROPAGATIONCAUSEDBYATMOSPHERICTURBULENCER.W.McMillanU.S.ArmySpaceMissileDefenseCommPOBox1500HuntsvilleAlabama358073801USAAbstractAtmosphericturbulencehasbeenshowntocausemeasurable

2、effectsonthepropagationofmicrowavemillimeterwavesignals.Althoughtheseeffectsarenotasstrongasthoseencounteredatvisiblewavelengthsbecauseoftheirvariationasf76wherefisfrequencythecontributionofthehuitystructurefunctionCQ2ma

3、kestheseeffectssignificantfmanyapplications.Inthispaperwepresentresultsofcalculationsmeasurementsoftheeffectsofatmosphericturbulenceonmillimeterwavesignalsat117140173230GHzaswellascalculationsmeasurementsoftheseeffectsat

4、10GHz.Theagreementbetweentheeticalmeasuredvaluesisconsideredgoodfthistypeexperiment.BackgroundDuringaseriesofmeasurementsofmillimeterwavepropagationthroughdustsmokein1977J.J.GallagherR.W.McMillanthenwkingattheGegiaTechRe

5、searchInstituteobservedlargeintensityfluctuationsof94140GHzsignalspropagatingthroughclearair.Althoughthisobservationwasnotsurprisinginlightofatmosphericturbulencetheywhichpredictscontributionstotheindexofrefractionstruct

6、ureparameterCn2fromboththetemperaturestructureparameterCT2thehuitystructureparameterCQ2aswellastheircrosscrelationCTQatmillimeterwavefrequenciesitwassurprisingtothemicrowavemillimeterwavecommunitiesbecauseithadrarelyifev

7、erbeenobservedbefe.AreptonthesemeasurementsledtosupptfromtheU.S.ArmyResearchOfficefmedetailedmeasurementsofthesephenomenaincludingcarefulmicrometerologicalinstrumentationfacterizationofthestructureparametersmentionedabov

8、ecrelationoftheseobservationswithmillimeterwavemeasurements.ThisseriesofexperimentswascarriedoutwiththesupptcollabationoftheNationalOceanicAtmosphericAdministrationprimarilyresponsiblefmeteologicalinstrumentationbytheaut

9、hcolleaguesattheGegiaTechResearchInstitute.TheresultsofthesemeasurementswhichweremadeatasitenearChampagneUrbanaIllinoischosenfthehomogeneityofitsterrainaregiveninseveralpapersfexample[12].Theseresultswillbediscussedinmed

10、etailinsubsequentsections.Apotentiallyseriousproblemfmicrowavemillimeterwaveradarsystemsinparticularisthatofangleofarrivalofthesignalsscatteredbytargetscausedbyturbulenceinducedwavefrontdisttion.Theangleofarrivalθisgiven

11、byθ=λ?2πdwhere?isthephasedifferenceinthewavefrontmeasuredoverthepathd.FmostradarscenariostheAOAisnegligiblebutinthosecaseswherethewavefrontmusttravelthroughgreatdistancesintheatmosphericboundarylayerfexampleinlongrangelo

12、wangletrackingapplicationsAOAcanbesignificant.MeasurementsofAOAFigure1.Experimentalconfigurationftheturbulencemeasurements.Figure2.Intensityfluctuationsmeasuredat140GHzMicrowaveRadarAngleofArrivalTheeffectsofatmospherict

13、urbulenceonradarangleerrsaregenerallysmallbutinthosecaseswherearadarisrequiredtoguideamissilewithoutaseeker(commguide)afewmicradiansoferrmaybeenoughtocausethemissiletomissitstarget.Inthispaperwecomparetwomethodsofcalcula

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