a limitedscan phased array antenna.docx

a limitedscan phased array antenna.docx

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alimitedscanphasedarrayantenna

alimited-scanphasedarrayantennawithwidely-spacedsmall-aperturecircularlypolarizedhighly-efficienthornelements

Abstract---Asmall-apertureantennawithawavedirector,acircularpolarizer,aconicalhornandtwocoaxialinputports,isuesedasaradiatingelementforalimited-scanphasedarraytoshapetheflat-toppedpatterninX-Bandinthispaper.Thehornantennaelementhascharacteristicsofsmallaperture,highgain,high-efficiency,lowsidelobe,2GHzbandwidthandtransmissioncircularpolarizationwave.Thedistancesbetweentheseelements（elementspacing）aremorethanonewavelengthinthelimited-scanphasedarray.However,theunwantedgratinglobeseffectsbesidethemainbeam,whichresultfromwidely-spacedhighefficientelements,areseriousproblems.Inordertosuppressthegatinglobesandhaveexcellentperformance,thelimited-scanphased-arrayantennaconsistof7（alongX）by7（alongY）equallyspaced,highefficientelementsisanalyzedandsimulatedbyHFSS;Also,acompactlargeaperiodicoctagonalarraywithunequallyspaced1664-elementsisdesigned.Itisworthmentioningthatithavebestsuppressionofgratinglobes（below-25dB）andbestperformancecomparedwithotherthreeoctagonalantennaarraysconfigurationcalculatedbyBorlandC++.AlongX,Y,thescanrangoflimited-scanphasedarraysareall

inmystudy.

IndexTerms--high-efficiencyelement,wavedirector,circularpolarization,phased-array,gatinglobesaperiodicoctagonalarray

1.INTRODUCTION

Thearraywithwidely-spacedelements,inotherwords,anarrayusingfewerelements,isoneofthedirectionsinphased-arrayradarantennastoday,whichnotonlymeanslowermanufacturingcosts,butalsomeans（implies）lighterweightofthearraysurface,lesselectricitydemandandbetterventilation.Thisformhasconsiderableadvantagesinapplicationsoflarge-scaleactivephasedarrays,becausethewideelementspacing（longdistanceofelements）canreducemutualcoupling[1]betweentheelementsinanarray,andtheperformanceofelementsinanarrayislittledifferentfromitoftheelementalone.However,whenthedistancebetweenelementsaremorethanonewavelength,gratinglobes[2]areinevitable,whichwillcausemulti-directional（multi-angle）emission,receivefuzzyinformationandwasteenergy.Soitisnecessarytosuppressthegratinglobes.Thereare（thereexist）twowaystosuppressthegratinglobes:

oneisusingactiveelementpatterncontrol[3],theotherisusingaperiodicarrangementofelements[4-5].Besides（Inaddition）,usingfewerelementstoreachahighlygainandaneffectivelong-rangeofarrayantennaisalsothetarget,so,thedesignoftheantennaelementisessential.

Indesigningacircularly（circular）polarizedantennaelement,oneof（the）mostimportantgoalsistofindtheoptimalradiatingthatmeetsasetofperformancecriteriathatusuallyincludeaxial,gainandsoforth.Circularpolarization,comparedto（把...比作）（with）linearpolarization,allowsforgreaterflexibilityinorientationanglebetweenreceiverandtransmitter,weatherpenetration,bettermobility,andreductioninmutil-pathreflectionandotherkindsofinterferences[1,2].So,circularpolarizedantennashavequiteextensiveusing（application）,suchas（forinstance）,communications,radar,electronicwarfare,telemetry,remotesensing,astronomy.However,Circularpolarizedantennaconsistsoftwocategories,oneisformedbytheantennaitself,theotherisformedbyacircularlypolarizer,.Thefirstcategoryhasseriousdepolarizationinanarraybecauseof（onaccountof）mutualcoupling,thesecondhaslittlemutualcouplinginthearraywithoutdepolarizationphenomenonduetothecircularpolarizerplacedinthewaveguide.Inthispaper,thesecondformisused（empolyed）,andonthebasisofsummingupthepreviouswork[]designedStepped-septumpolarier.

Theantennaelementisahighefficientelement,thatishavinghighgain.Anovelwavedirectorisdesignedinordertoincreasethegain.Alotofthesehighefficientelementscomposedofalargeaperiodicoctagonalarray,（largeaperiodicoctagonalarrayiscomposedofthesehighlyefficientelements）.Thislargelimitedscanphasedarraycanbeusedfortargetsurveillance,capture,tracking,recognitionandsoon（soforth）.

Inthefollowingsection,adetaileddesignandanalysisprocessofahighlyefficientelementwithawavedirector,apolarizerandassociatedfeedstructureispresented.Theefficientelementisfeedbyeithercoaxialsdirectly.thepatternofthe7*7phased-arrayinX-bandwiththis（these）highlyefficientelementsobtainedbyusingthesimulationsoftwareAnsoftHFSSisanalyzed.Furthermore,aconstructionofalargespacinglimitedscanaperiodicoctagonalarraywith1664-elementshavebeendesignedandresearched.TheresultswhichderivesfromtheaperiodicoctagonalarrayareobtainbyusingBorlandC++andOriginpro.weonlyfocusedonthepassiveantennapartofthephasedarraysystem,notincluded（exceptfor）theactiveT/Rmodulesinthispaper.

1.SINGLEHIGHEFFICIENTELEMENTDEVELOPMENT（SinglehighefficientElementDevelopment）

thestructureofthehighlyefficientelementantennawhichconsistoffourmajorparts:

awavedirector,apolarizer,aconicalhorn,twocoaxialinputports,asisshowninfig.1.Becausetheelementantenna（antennaelement）ishighlyefficientelement,andconsideredthehornantennahave（has）lowVSWR,widebandwidth,powercapacity,andmanyotheradvantages,so,itissuitabletobeaelementofthearray.（itisfeasibletoselecttheseelements）.Ifhornshaveappropriateaperture,agoodradiationcharacteristicswillbereceived.Althoughtheapertureofthehornisfixedto38mminmystudy.awavedirector,consistofeightlayered,stackupdielectric-slabandincenterofeachdielectric-slabliesinadisk,whichisdesignedandarrangedabovethehornapertures,theaimofthewavedirectoristoguidethewavetransmissionandconcentratetheenergy.Theroleofthedielectric-slabsarealsofixeddisks.Themorenumberofdisks,thestrongertheabilitytoguidewave,ifdisksexceedacertainnumber,theinfluenceofguidingwaveisinsignificantbecausetheinductioncurrentontheedgeofeachdiskisweaken.

dielectric-slabs’permittivityis1.15,thethicknessoffirstdielectric-slababovethehornaperture,is11mm,theothersevendielectric-slabsareall9mm,theradiusofeachdiskis4mm,4mm,4mm,4mm,4.5mm,4.5mm,4.5mm,4mmrespectivelyandthethicknessareall0.5mm,theheightofhornis19mm.Thespecificstructureisasshowinfigure1.

Comparedwithotherpolarizer,septumcircularpolarizerbe（is）abletoachievedualcircularpolarizationwithoutexternalorthogonal.Thepolarizerconsistsofathinconductiveseptum,whichdivideacircularwaveguideintotwoidenticalsemicircularwaveguides.Theheightoftheseptumequalsthediameterofthecircularwaveguide.Andtheheightgraduallydecreasestozeroindiscretesteps.Theexcitationtakeplaceonthewaveguide.Byselectingtheappropriatedimensionsoftheseptum’ssteps,linearpolarizedwavedecomposedintoequalamplitude,phasedifferenceis90°circularpolarizedwavesthroughtheseptum’ssteps.Thesizeofthecircularpolarization（CP）asshowninfigure2.

Thecoaxialinputportsverticalmetalseptum,theprobeconnectedtocoaxialinputportisinsertedintothecircularwaveguide,thelengthofprobeextendshavesignificanteffectonCPperformanceandVSWR.Accordingtothespecificsituationtoadjustthenumberandradiusofthedisksandtheheightofthedielectric-slab.Copperwasusedthroughoutthedesignforallthemetallicparts.EitherfeedportcanbeformedLeft-HandCPorReft-HandCP.thesimulationresultsareshowninfigure4（when）

thepatternin

planeisalmostoverlappedinthe

plane,andtheVSWRislow.Generallyspeaking,athighfrequenciesthesmallapertureantennaelementisdifficulttoachievesuchahighgain,however,thishighlyefficiencyradiatingelementreachedabout16dBgainvaluewith38mmapeature.Simultaneously,ARmeetstherequirementwonderfullyasdepictsinfig.4.Theefficientunitcanconstitutealargespanlimitedscanningphasedarray,alsocanformotherarrayantennawhichusedinthemilitaryfieldssuchasradar,remotetelemetry.

figure1.Athree-dimensionalviewofthehighlyefficientelementantenna

figure2.Thedimensionsofthepolarizer,refertoTable1fordetails.

Table1.thedimensionsofthepolarizer（unit:

mm）

a

b

c

d

e

f

g

h

i

j

k

l

2.7

4.5

8.3

13.0

18.6

23.8

6.7

14.3

10.3

9.3

2.9

25.6

figure3.TheVSWRofahighefficientelement

Figture4（a）.ARofelementantennainthe

plane

Figture4（b）.Gainofelementantennainthe

plane

3.Theanalysisof7by7limitedscanequally（uniform）spacingphased-arrayantenna

A7*7arrayisformed（by）theabove-describedhighlyefficientelement,the（elementspacing）is1.2

Advantagesanddisadvantagesoccuredwhenelementspacingisbeyondonelambda.Accordingtotheformula

（1）,when

，itisinevitabletoappeargratinglobes,andamoreseriousproblemisthatthegratinglobewillrisewhenscanning.Inarray,wavedirectoralsocanguidewavetransmission,maketheenergyconcentratedinonedirection,theefficiencyishigherthangeneralelementantenna.Besides,therearemutualcouplingbetweenelementsinarray,usually,mutualcouplingmakethepatterndistort,anddepolarizationisobvious.however,inmyresearch,thedistancebetweenantennaelementsis1.2lamda,which（reducesthemutualcouplingeffects）,inaddition,eachelementofthecircularpolarizerplacedinthecircularwaveguide,almostnotproducesinteractiontoinfluencethecircularpolarizationofarray.Th