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.TheBWoftheMSAisinverselyproportionaltoitsqualityfactorQandisgivenby5.2BroadbandTechniques5.2.1DefinitionofBW34Basictechniques：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

resonantcircuit25

(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)、DesignwithaRectangularPatch464748(二)、DesignwithaCircularPatch4950(三)、DesignwithaTriangularPatch51525.4.3UseofU-slot44%24%18%53UWBtechnologyhasbeenusedintheareasofradar,sensingandmilitarycommunicationsduringthepast20years.UWBhasanumberofencouragingadvantagesthatarethereasonswhyitpresentsamoreeloquentsoluti