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Chapter5BroadbandingofMicrostripAntennas
Microstripantennashaveanumberofusefulproperties,butoneoftheseriouslimitationsodtheseantennashasbeentheirnarrowbandwidthcharacteristic.TheimpedancebandwidthofatypicalMPAislessthan1%toseveralpercentforthinsubstratessatisfyingthecriteriah/λ0
<0.023forεr
≈10toh/λ0
<0.07forεr≈2.3.Thisisincontrastto15%to50%bandwidthofcommonlyusedantennaelementssuchasdipoles,slots,andwaveguidehorns.
5.1Introduction1
Chapter2BroadbandingofMicrostripAntennasResearchershavebeenengagedinremovingthislimitationforthepast20years,andhavebeensuccessfulinachievinganimpedancebandwidthofupto90%andgainbandwidthupto70%inseparateantennas.Mostoftheseinnovationsutilizemorethanonemode,giverisetoincreaseinsize,height,orvolume,andareaccompaniedbydegradationoftheothercharacteristicsoftheantenna.Increaseinbandwidthcanalsobeachievedbyasuitablechoiceoffeedingtechniqueandimpedancematchingnetwork.5.1Introduction2TheVSWRorimpedanceBWoftheMAisdefinedasthefrequencyrangeoverwhichitismatchedwiththatofthefeedlinewithinspecifiedlimits.TheBWoftheMSAisinverselyproportionaltoitsqualityfactorQandisgivenby5.2BroadbandTechniques5.2.1DefinitionofBW3
ImpactFactors
changedirection
changeofQ
ImpactforBW
Width/Length
increase
decrease,decreaseBWincreaseLosstangentofdielectric
increase
decreaseBWincrease
Effectivedielectricconstant
decrease
decrease,decreaseBWincrease
Heightofsubstrate
increase
decrease,decrease,increaseBWincrease4Basictechniques:DecreaseequivalentresonantcircuitQExtraresonantfrequency:Parasiticpatch、LCresonantcircuit、LoadshortprobeAddimpedancematchingnetworkOthertechnique5.2.2BroadbandingTechniquesofMAs5
1.Thicksubstratewithlowerdielectricconstant
(一)、Eshapepatchantenna
6
EpalneradiationpatternHpalneradiationpattern
2.04GHz~2.91GHz,35.1%
7(a)f=2.13GHz(b)f=2.7GHzCurrentdistributiononthepatchantennaMaximumvarietylessthan1dBMaximumGainobtained9.05dBi
8(二)、LshapeMAwithelectromagneticcouplingfeed
9ReturnLoss(S11)Inputimpedanceplot(3.86GHz~5.8GHz),40.2%
EpalneradiationpatternHpalneradiationpattern
10
11(三)、RidgeshapegroundplaneMPA
12EpalneradiationpatternHpalneradiationpattern2.02GHz~3.9GHz,64%
13
14(四)、MAfeedingwithmetalslant2.15GHz~4.76GHz
,BW=75.5%
15(五)、MAfeedingwithMeanderprobe
161.6GHz~2.24GHz,640M
,
33.3%1.64GHz~2.16GHz
,540M,27%EpalneradiationpatternHpalneradiationpattern
17Maximumvarietylessthan1.45dBMaximumGainobtained9.19dBi
18(一)、Parasiticpatch(coplanar)2.Extraresonantfrequency19(一)、Parasiticpatch(coplanar)202.66GHz~3.06GHz,400M,14%
2.65GHz~2.71GHz,60M,2.2%
21(一)、Parasiticpatch(Dual-layer)222324
(二)、LC
resonantcircuitAntennatypeBW(S11≤-10dB)
ResonantfrequencyNormalMA20MHz,1.5%f0=1345MHzMAwithMicrostriplineinside75MHz,5.6%f1=1327MHzf2=1360MHz25
(三)、Loadshortprobebetweenpatchandgroundplane3.62GHz~7.32GHz,67.5%
BluetoothAntenna-EmbeddedPIFA
26(一)、Singleresonantbranchmatchingtechnique
3.375GHz~3.855GHz,13%
3.Addimpedancematchnetwork27(二)、Applicationofbranchmatchincoaxialprobefeeding
281.78GHz~2.31GHz,26%
EpalneradiationpatternHpalneradiationpattern
29
Employing3-DVshapepatchantenna
4.Othertechnique301.86GHz~5.36GHz,97%
1.95GHz~3.04GHz,44%
Eplaneradiationpattern
31Hplaneradiationpattern
325.3Multi-bandMicrostripantenna5.3.1Multi-patch33345.3.2Multi-modeofsinglepatch5.3.3Loadedsinglepatch355.3.3Loadedsinglepatch36Personalmobilecommunicationandotherminiaturizedcommunicationsystemsneedasmall-sizedMA.ThesizeoftheregularlyshapedMAoperatingintheUHFbandisquitelargebecauseitsresonantlengthisinverselyproportionaltofrequency.Todesignasmallerantennaatthesefrequencies,conventionalMAconfigurations,suchasrectangularandcircularconfigurations,needtobemodified.Also,todesignabroadbandantennaarray,theelementshouldhavelargeBW.Compactbroadbandelementsneedtobedesignedforthispurpose.5.4CompactBroadbandMicrostripAntennas37CompactMSAscanbedesignedwithsubstratehavingahigherdielectricconstantεr.Inthiscase,thesizeoftheregularlyshapedMSAswillbemuchsmallerthanthatofthelowdielectricconstantsubstrateatagivenresonancefrequency,buttheBWissmall.ThissectiondescribesvariouscompactMSAconfigurationsthatareobtainedbymodifyingregularshapes,suchasrectangular,circular,andtriangularpatches,byusingshortingpostsorbycuttingslotsinthemetallicpatch.385.4.1UseofaShortedPatch(一)、Probe-fedShortedPatchorPIFA3940(二)、Aperture-CoupledShortedPatch4142(三)、Microstrip-Line-FedShortedPatch4344(四)、CapacitivelyCoupledorL-Probe-FedShortedPatch455.4.2UseofaChip-resistorandChip-capacitorLoadingTechnique(一)、DesignwithaRectangularPatch46ConventionalPatchShort-ProbeChip-Resistorf01.9GHz722MHz710MHz
BW1.9%1.4%9.3%4748(二)、DesignwithaCircularPatch4950(三)、DesignwithaTriangularPatch51525.4.3UseofU-slot44%24%18%53UWBtechnologyhasbeenusedintheareasofradar,sensingandmilitarycommunicationsduringthepast20years.UWBhasanumberofenco
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