Research Article A Time Modulated Printed Dipole Antenna Array for Beam Steering Application

12 Pages·2017·3.56 MB·English

Hindawi
International Journal of Antennas and Propagation
Volume 2017, Article ID 3687293, 11 pages
https://doi.org/10.1155/2017/3687293
Research Article
A Time Modulated Printed Dipole Antenna Array for
Beam Steering Application
RuchiGahley1andBananiBasu2
1DepartmentofElectronicsandCommunicationEngineering,ThaparUniversity,Patiala147004,India
2DepartmentofElectronicsandTelecommunicationEngineering,NationalInstituteofTechnology,Silchar788010,India
CorrespondenceshouldbeaddressedtoBananiBasu;basu [email protected]
Received5October2016;Revised18December2016;Accepted4January2017;Published16February2017
AcademicEditor:SotiriosK.Goudos
Copyright©2017RuchiGahleyandBananiBasu. This is an open access article distributed under the Creative Commons
AttributionLicense,whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkis
properlycited.
Thispaperpresentstimemodulatedbeamsteeredantennaarraywithoutphaseshifters.Thebeamsteeringisanalyzedconsidering
a two-element time modulated antenna array (TMAA) of printed dipoles with microstrip via-hole balun. The proposed array
resonatesattheIndustrial,Scientific,andMedical(ISM)radiobands,2.45GHzand5.8GHz,andofferswidebandwidthinherited
duetomodifiedstructureofgroundplane.Arrayelementsareexcitedbycomplexexponentialexcitationsignalthroughbroadband
powerdividerandradiofrequency(RF)switchestoachieveamplitudeandphasevariationwithoutphaseshifters.Differential
EvolutionalgorithmisusedtomodifythetimesequencesoftheRFswitchesconnectedtotheantennastogenerateradiationpattern
withoptimumdynamicefficiencybysuppressingsidebandradiations.Alsoswitch-ontimeinstantofRFswitchconnectedtothe
subsequentelementismodulatedtosteerthebeamtowardsdifferentdirections.Theproposedprototypeisfabricatedfollowedby
parametricoptimization.Thefabricationresultsagreesignificantlywellwithsimulatedresults.
1.Introduction Differenttimesequences[4–7]wereusedtocontroltheRF
switching. Different optimization strategies have been used
Antennaarraysarewidelyusedincommunicationsystemsto in TMAA to synthesize its radiated power pattern [8, 9]
obtain desired radiation characteristics. Various techniques to realize beam steering [10], beam forming [11–14], null
forsynthesizingarraysareavailableinliterature[1].Phased synthesis [15, 16], and direction finding [17] without using
arrayantennasarewidelyusedforconventionalbeamscan- conventionalphaseshifters.ApplicationofTMAAincogni-
ning,beamsteering,andadaptivebeamformingapplications tiveradiohasbeenanalyzedin[14].In[18],TMAAshasbeen
byadaptingtheexcitationamplitudeandphasedistribution applied to achieve directional modulation for secure com-
[2].Thelimitationsassociatedwiththephasedarrayantenna munication. Printed antenna owing to variety of beneficial
togenerateradiationpatternswithvariousstringentdesign- propertiesincludinglightweight,lowprofile,andlowcosthas
ingconstraintsarecost,size,powerconsumption,andhigh becomeexplosivelypopularandwidelyinvestigatedinarti-
complexity.Asubstantialamountofeffortshasbeendevoted cles[19–22].Widebandprintedantennasutilizedinmodern
to develop low cost highly reliable phased array antenna wireless communication systems are presented in [23–27].
sinceearly1960s.Timemodulationappliedtolinearantenna TMAAasaversatileadequateradiationsystemformodern
array is a technique to adapt its radiated power pattern by wireless applications has increased significantly over recent
periodically enabling and disabling the excitations of the past.
individual array elements [3]. Since early 2000s there has ThepresentedarticleproposesTMAAofprinteddipoles
beenrenewedinterestintakinguptheinvestigationsonthis for beam steering without using phase shifters. The tra-
fieldduetothearrivalofthehighperformanceRFswitches. ditional printed dipoles using novel U-shaped ground
2 InternationalJournalofAntennasandPropagation
Control signal from Control signal from
CPLD test board (fp) RF RF CPLD test board (fp)
switch switch
Complex exponential
signal
RF IN
Figure1:SimplifiedblockdiagramoftheproposedTMAA.
planeandquarterwavelengthmicrostripvia-holebalunare Here𝑓0 ≫𝑓𝑝(𝑓𝑝 =1/𝑇𝑝,𝑇𝑝istheTMperiod).𝛽=2𝜋/𝜆
designed at 2.45GHz and 5.8GHz inspired by [20]. Intro- isthefreespacewavenumber,𝜆=𝑐/𝑓0isthewavelength,and
duction of the U-shaped ground plane reflects the electro- 𝑐isthespeedoflightinfreespace.
magneticwavestowardsthefeedingdirection.Itimprovesthe
{𝑈 (𝑡),
rtievfleelycttihonancotheffieVci-esnhtaapneddbsrtoruadcteunrsethuesebdanindw[2i0d]t.hThmoerdeiepffoelecs- 𝐼𝑛(𝑡)={{𝑈𝑛𝑛(𝑡)𝑒−𝑗2𝜋𝑓𝑝𝑡, for 𝑛=1,2. (2)
are connected through a broadband power divider ranging
from 2.1GHz to 7GHz and PIN diode single pole single 𝑈𝑛(𝑡) is the time switching function of the RF switches
throwRFswitches.DEisappliedtoobtainthetimesequence modellingtheperiodicon-offtimeoftheswitches.Thus
to suppress the side band power level (SBL). Applicationof
{1, 𝑘𝑇 +𝑡 ≤𝑡≤𝑘𝑇 +𝑡 +𝜏 ,
complexexponentialsignalsteersthebeamtowardsdifferent 𝑈𝑛(𝑡)={ 𝑝 on 𝑝 on 𝑛 (3)
directions as the switching time sequences of RF switches {0, otherwise.
are modulated. Article [12] has simulated a beamforming
network for TMLA using Artificial Bees Colony algorithm. 𝜏𝑛 are the switch-on duration of the RF switches con-
Howeverthepresentarticlehassuccessfullyimplementedthe nected to 𝑛th element and 𝑘 is an integer. Due to the
designstructureofdualbandTMbeamsteeredarrayusing periodicity of the modulating pulse functions 𝐼𝑛(𝑡) can be
DE. decomposed into Fourier series with different frequency
components,givenby
The antenna structure is rigorously optimized through
simulation using CST microwave studio to realize wide ∞
bandwidthresponsesatthetwoproposedresonances.Exper- 𝐼𝑛(𝑡)= ∑ Γ𝑛(𝑚)𝑒𝑗2𝜋𝑚𝑓𝑝𝑡, (4)
𝑚=−∞
imental testing of the fabricated antenna array shows good
agreThemeernetstwoifththtehepaspimeruilsatoerdgarnesizueltds.asfollows.Theproblem Γ1⟨𝑚⟩(𝑡)= 𝑇1 ∫𝑇𝑝𝑈𝑛(𝑡)𝑒−𝑗2𝜋𝑚𝑓𝑝𝑡𝑑𝑡, (5)
𝑝 0
ismathematicallyformulatedinSection2.Section3provides
tThMeAoAutlairneedoefscDribEe.dThineSdecetsiiognn4s.pAecsiefitcoatfinounms eorficparlorpeosuseltds Γ2⟨𝑚⟩(𝑡)= 𝑇1 ∫𝑇𝑝𝑈𝑛(𝑡)𝑒−𝑗2𝜋(𝑚+1)𝑓𝑝𝑡𝑑𝑡, (6)
𝑝 0
is reported and discussed in Section 5. Finally the paper is
concludedinSection6. Γ⟨𝑚⟩ = 𝜏𝑛 sin(𝜋𝑚𝑓𝑝𝜏𝑛)𝑒−𝑗𝜋(𝑚+𝑛−1)𝑓𝑝(2𝑡on+𝜏𝑛). (7)
𝑛 𝑇 𝜋𝑚𝑓 𝜏
2.TheoreticalBackground 𝑝 𝑝 𝑛
Underthehypothesesthat𝑓𝑝 ≪ 𝑓0andΔ𝑓𝑠 < 𝑓𝑝,where
Consider an array of two collinear dipoles with spacing 𝑑 Δ𝑓𝑠 is the maximum bandwidth of the received signals, the
positioned along the 𝑧-axis as shown in Figure 1. Both the signalattheworkingfrequency𝑓0 canbethenextractedby
arrayelementsareexcitedusingacomplexexcitationsignal filteringouttheSRandeventuallythereceivedsignalturns
𝑒−𝑗2𝜋𝑓𝑝𝑡 and controlled by a high-speed RF switch having outatinfinitenumberofharmonictermsspacedat𝑚𝑓𝑝(𝑚∈
𝑓𝑝. When a plane wave of frequency 𝑓0 is incident at an 𝑍)from𝑓0.Accordingly,thearrayfactorat𝑓0turnsouttobe
angle 𝜃 with respect to the normal of the array, the far
2 𝜏
field pattern of the array considering the element pattern 𝐹⟨0⟩(𝜃)=𝑒𝑗2𝜋𝑓0𝑡∑ 𝑛𝑒−𝑗𝜋(𝑛−1)𝑓𝑝(2𝑡on+𝜏𝑛)𝑒𝑗𝛽𝑛𝑑cos𝜃,
𝑇
is 𝑛=1 𝑝
(8)
𝐹(𝜃)=𝑒𝑗2𝜋𝑓0𝑡∑2 𝐼𝑛(𝑡)𝑒𝑗𝛽𝑑𝑛cos𝜃[cos((𝜋si/n2)𝜃cos𝜃)]. (1) 𝐹⟨𝑚⟩(𝜃)=𝑒𝑗2𝜋𝑓0𝑡∑2 Γ𝑛⟨𝑚⟩(𝑡)𝑒𝑗𝛽𝑛𝑑cos𝜃.
𝑛=1 𝑛=1
InternationalJournalofAntennasandPropagation 3
Via hole
L
2 W
1
L
p
W
p
g
W
b L
g G
ℎ
d
Microstrip via hole
SMA
W
g
(a)
L
L3
Top
L2
W L1 W2 W3 W4
W1 R R R
Bottom
(b) (c)
(d) (e)
Figure2:ElementsoftheTMAA:(a)configurationoftheantennaarray;(b)prototypeoftheantennaarray;(c)configurationofthepower
divider;(d)prototypeofthepowerdivider;(e)prototypeoftheRFswitchandCPLDtestboard.
Theaveragepowerdensityradiatedbythearrayover𝑇𝑝 Thususing(8),weevaluatetheexpressionofthepower
radiatedatcentralfrequency(𝑃0)andatthesidebands(𝑃SR)
𝑆(𝜃)= 𝑇1𝑝 ∫−𝑇𝑇𝑝𝑝//22[Re⟨𝐹(𝜃)⟩]2𝑑𝑡. (9) 𝑃0 =2𝜋∑2 (𝑇𝜏𝑛)2,
𝑛=1 𝑝
Sothetotalpowerradiatedcanbecalculatedusing (11)
2𝜋 𝜋 𝑃 =2𝜋∑2 𝜏𝑛 (1− 𝜏𝑛).
𝑃(𝜃)=∫ ∫ 𝑆(𝜃)sin𝜃𝑑𝜃𝑑𝜙. (10) SR 𝑇 𝑇
0 0 𝑛=1 𝑝 𝑝
4 InternationalJournalofAntennasandPropagation
0 −3
−3.5
−5
−4
B) B)
d −10 d −4.5
meter ( −15 meters ( −5−.55
-paraS −−2250 -paraS −6−.56
−7
−30 −7.5
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
Frequency (GHz) Frequency (GHz)
S11simulated S11measured S21
S simulated S measured S
21 21 31
S simulated S measured
31 31
(a) (b)
200
ees) 150
gr
de 100
n
e i 50
has 0
p
ers ( −50
et −100
m
ara −150
p
-S −200
1 2 3 4 5 6 7 8
Frequency (GHz)
S21
S
31
(c)
Figure3:(a)Simulatedandmeasuredscatteringparametersofpowerdivider.(b)Magnitudeofsimulated𝑆21and𝑆31parameter.(c)Phase
ofsimulated𝑆21and𝑆31parameter.
Sothedynamicefficiencyofthearrayis 3.DifferentialEvolution
𝜏2+𝜏2 Differential Evolution (DE) proposed by Storn and Price
𝜂= 𝑇 (𝜏 +1𝜏 )−2𝜏2−𝜏2. (12) [28,29]iswellknownpopulationbasedsimpleandefficient
𝑝 1 2 1 2 method for global optimization. DE algorithm consists of
thefollowingbasicsteps:initialization,mutation,crossover,
In order to suppress the SLL and enhance the dynamic
selection,andtermination.
efficiency,theDEalgorithmisappliedastheglobaloptimiza-
tionmethod.Toachievethedesigngoalthefollowingfitness (1) Initialization of Population. DE searches for a global
functionisformulatedforminimizationoveriterationsusing optimumwithinacontinuoussearchspaceofdimension𝐷.
DE Generate𝐾 𝐷–dimensionalpopulationoftargetvectorsfor
1 eachgeneration𝐺.
Fitness(𝑡on,𝜏𝑛)=𝑘1SLL+𝑘2(𝜂), (13) 𝐴⃗ =[𝑎1 ,𝑎2 ,𝑎3 ,...,𝑎𝐷],
𝑖,𝐺 𝑖,𝐺 𝑖,𝐺 𝑖,𝐺 𝑖,𝐺
(14)
where 𝑖=1,2,3,...,𝐾.
while SBL at the first sideband is not allowed to rise
beyond −25dB. The constants 𝑘1 and 𝑘2 are the corre- Targetvectorswithbetterresultsmaybefoundinadefinite
sponding weighing factors of SLL and dynamic efficiency, regionofsearchspacewithmaximumandminimumbounds
respectively.Inthedesigningproblem,equalweightage(𝑘1 = ineachdimensionas
𝑘2 = 1) of both the parameters is considered. The switch- 𝐴⃗ =[𝑎1 ,𝑎2 ,...,𝑎𝐷 ],
on time (𝑡on) and switch-on duration (𝜏𝑛) of each element max max max max
(15)
areconsideredaspopulationvectorsandvariedinorderto 𝐴⃗ =[𝑎1 ,𝑎2 ,...,𝑎𝐷 ].
minimizethefitnessfunction. min min min min
InternationalJournalofAntennasandPropagation 5
0 0
−5
−5
meter (dB) −10 meter (dB) −−1150
-paraS −−2105 -paraS −−2250
−25 −30
0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8
Frequency (GHz) Frequency (GHz)
d=2mm d=5mm Gℎ=6mm Gℎ=12mm
d=3mm d=6mm Gℎ=8mm Gℎ=14mm
d=4mm Gℎ=10mm
(a) (b)
0
−5
−10
B) −15
d
er ( −20
et −25
m
a −30
par −35
-S −40
−45
−50
0 1 2 3 4 5 6 7 8
Frequency (GHz)
g=1mm g=2.5mm
g=1.5mm g=3mm
g=2mm
(c)
Figure4:Optimizedreturnlossofantennaarray:(a)𝑆11fordifferent𝑑;(b)𝑆11fordifferent𝐺ℎ;(c)𝑆11fordifferent𝑔.
0
−5
B)
d −10
er (
et −15
m
a
ar −20
p
-S
−25
−30
0 1 2 3 4 5 6 7 8
Frequency (GHz)
Measured
Simulated
Figure5:Simulatedandmeasuredreturnlossofantennaarray.
The𝑗thcomponentofthe𝑖thvectorisinitializedas (2)Mutation.Afterinitialization,adonorvector𝑀⃗𝑖,𝐺corre-
𝑎𝑗 =𝑎𝑗 +rand𝑗(0,1)⋅(𝑎𝑗 −𝑎𝑗 ), sponding to best population member 𝐴⃗best,𝐺 in the current
𝑖,0 min 𝑖 max min generationiscreatedthroughmutation.
(16)
𝑗∈{1,2,3,...,𝐷}, 𝑀⃗𝑖,𝐺=𝐴⃗best,𝐺+𝐹⋅(𝐴⃗𝑟𝑖,𝐺−𝐴⃗𝑟𝑖,𝐺). (17)
1 2
whererand𝑗(0,1)isauniformlydistributedrandomnumber Theindices𝑟𝑖 and𝑟𝑖 aremutuallyexclusiveintegersandran-
𝑖 1 2
lyingbetween0and1. domlychosenfromtherange(1,2,...,𝐾).𝐹iscalledscaling
6 InternationalJournalofAntennasandPropagation
(dBV/m2)
−56.4 3
−62.6
2
10
−66.4
8
6
n −70.1 1
er 4
n patt 2 −73.9
o 0 0
diati −2 −81.4
a
R −4
−6 −88.9 −1
−8
3 −96.4
2 3 −2
1 2
0 1
Y −1 0
−1
−2 −2 X −3
−3 −3 −3 −2 −1 0 1 2 3
(a) 3Dradiationpatternplot (b) Contourplot
Figure6:Optimizedradiationpatternatcentrefrequency2.45Ghz.
(dBV/m2)
−37.7
10 −44
8
−47.7
6
n 3
er 4
patt 2 −51.5
n 2
atio 0 −59
di −2
Ra −4 −62.7 1
−6
−8 −70.3 0
3
2 −77.7
3 −1
1
2
0 1
Y −2
−1 0
−1
−2 X
−2 −3
−3 −3 −3 −2 −1 0 1 2 3
(a) 3Dradiationpatternplot (b) Contourplot
Figure7:Optimizedradiationpatternatcentrefrequency5.8Ghz.
factorwhichwillbetunedaccordingtothefitnessfunction the trial vector of the same index denoted as 𝑇𝑖⃗,𝐺 =
generatedbyeachvector.𝐴⃗best,𝐺isthebestindividualvector [𝑡𝑖1,𝐺,𝑡𝑖2,𝐺,𝑡𝑖3,𝐺,...,𝑡𝑖𝐷,𝐺].Thetrialvectorcreatedis
withminimumfitnessvalueinthepopulationatgeneration
𝐺(3.) Crossover. In crossover operation the donor vector 𝑡𝑖𝑗,𝐺={{𝑚𝑖𝑗,𝐺, if (rand𝑗𝑖 (0,1)≤CR or 𝑗=𝑗rand), (18)
mixes its components with the target vector 𝐴⃗𝑖,𝐺 to obtain {𝑎𝑖𝑗,𝐺, otherwise,
InternationalJournalofAntennasandPropagation 7
B) 0
d
n ( −10
atter −20
n p −30
o
ati −40
di
a −50
d r
e −60
z
mali −70
Nor −80
−200 −150 −100 −50 0 50 100 150 200
Theta (degree)
2.45GHz (f) 2.45GHz−1f
0 p
2.45GHz+1f
p
Figure8:Radiationpatternatcentrefrequency2.45Ghzandsidebands.
B) 0
d
n ( −10
er
att −20
p
on −30
ati
di −40
a
d r −50
e
z
ali −60
m
Nor −70
−200 −150 −100 −50 0 50 100 150 200
Theta (degree)
5.8GHz (f) 5.8GHz−1f
0 p
5.8GHz+1f
p
Figure9:Radiationpatternatcentrefrequency5.8Ghzandsidebands.
where CR is the crossover rate belongs the interval (0,1). ontheFR4dielectricmaterialofdielectricconstant4.4and
𝑗rand ∈ [1,2,...,𝐷] is a randomly chosen index which thickness 1.6mm. The configurations and prototype of the
differentiate trial vector 𝑇𝑖⃗,𝐺 from its corresponding target antenna array and power divider are shown in Figure 2
vector𝐴⃗𝑖,𝐺. adnimdetnhseiodnimofenthsieonasntaernenparaerseranyteids i1n36Tmabmle×1.3Th7memov.eThralel
(4) Selection. Selection is introducedto determine which of RF switch is realized by connecting a series capacitor, 10nf
thetargetortrialvectorssurvivestothenextgeneration.If before and after the pin diode, BAR63-02. Capacitors are
the fitness value of the trial vector is equal to or less than connectedtoprovidetheRFconnectivityandtopreventthe
thatofthecorrespondingtargetvectorthenthetrialvector dc.TheprototypeoftheRFswitchisshown inFigure2(e).
isselectedfornextgeneration;otherwisethetargetvectoris A rectangular pulse train of 3V at a repetition frequency
selectedfornextgeneration. of 1MHz is applied to bias the PIN diode. The CPLD
test board (Figure 2(e)) is programmed to generate the
(5)Termination.Ifterminationconditionisnotsatisfiedthe desiredrectangularpulseandcanbetunedfordifferenttime
executionisreturnedtoStep(2);otherwiseitisterminated. sequences.Theantennaarray,RFswitches,andpowerdivider
are connected through 50Ω SMA male/female connectors.
ThecomplexexponentialsignalandRFsignalsareprovided
4.PrototypeDesign
throughthesignalgeneratorandRFsource.
A prototype of the overall system is implemented and
presented in this section. The overall system consists of 2- 5.ResultsandDiscussion
element printed dipole antenna array, RF switches, pulse
generator, power divider, and an analog multiplier. The The proposed steering technique is experimented with an
antenna array, power divider, and RF switches are printed array prototype comprising of two microstrip fed printed
8 InternationalJournalofAntennasandPropagation
Table1:Structuralparametersofdipoleantennaarrayandpowerdivider.
Dipoleantennaarray(136mm×37mm) Powerdivider(41mm×30mm)
Partofdipole
Parameter Dimension Parameter Dimension
Thickness 1.6mm Substratethickness 1.6mm
PCBsubstrate 𝜀𝑟 4.4 𝜀𝑟 4.4
tan𝛿 0.0018 tan𝛿 0.0018
𝑑 2mm 𝐿 41mm
𝐺ℎ 6mm 𝑊 30mm
Groundplane 𝐿𝑔 10mm 𝐿1 12.56mm
𝑊𝑔 15mm 𝐿2 19mm
𝐿𝑝 13mm 𝐿3 4mm
𝑊𝑝 5mm 𝑊1 4mm
𝐿 16mm 𝑊2 3.057mm
Dipolearm
𝑊 6mm 𝑊3 3.83mm
Microstripbalun 𝑊𝑏 3mm 𝑊4 2.947mm
Via-holeradius 1mm 𝑅 100Ω
90 90
0 120 60 0 120 60
−5
−10
150 30 −10 150 30
B) −20 B) −15
e (d −30 e (d −20
ud 180 0 ud −25 180 0
mplit −30 agnit −20
A −20 M −15
210 330 −10 210 330
−10
−5
0 240 300 0 240 300
270 270
Simulated Simulated
Measured Measured
(a) (b)
90 90
0 120 60 0 120 60
−5 −5
−10 150 30 −10 150 30
B) −15 B) −15
e (d −20 e (d −20
ud −25 180 0 ud −25 180 0
mplit −20 agnit −20
A −15 M −15
−10 210 330 −10 210 330
−5 −5
0 240 300 0 240 300
270 270
Simulated Simulated
Measured Measured
(c) (d)
Figure10:Simulatedandmeasuredradiationpatternfordifferentvaluesof𝑡02 at2.45GHz.(a)𝑡02 = 0𝜇sec.(b)𝑡02 = 0.125𝜇sec.(c)
𝑡02=0.25𝜇sec.(d)𝑡02=0.375𝜇sec.
InternationalJournalofAntennasandPropagation 9
90 90
0
0 120 60 120 60
−5 −5
−10 150 30 150 30
B) −15 B) −10
d d
e ( −20 e (
ud 180 0 ud −15 180 0
plit −20 plit
m −15 m −10
A A
−10
210 330 210 330
−5 −5
0
240 300 0 240 300
270 270
Simulated Simulated
Measured Measured
(a) (b)
90
0
120 60
−5
−10
150 30
−15
B)
e (d −20
ud −25 180 0
plit −20
m
A −15
−10 210 330
−5
0 240 300
270
Simulated
Measured
(c)
Figure11:Simulatedandmeasuredradiationpatternfordifferentvaluesof𝑡02at5.8GHz.(a)𝑡02 = 0𝜇sec.(b)𝑡02 = 0.125𝜇sec.(c)𝑡02 =
0.375𝜇sec.
dipoles for dual band operation at 2.45GHz and 5.8GHz, layer are rigorously studied in order to obtain optimized
as shown in Figure 2. The structure of the printed dipoles designparameters,asshowninFigure4.Theprototypeofthe
is designed to provide good impedance matching over the antennaarrayisfabricatedandpresentedinFigure5.Theon
operatingfrequencybands.Thefeednetworkoftheproposed stateinsertionlossandoffstateisolationoftheRFswitchare
TMAA is composed of an ultra-wideband power divider studiedandfound0.6dBand25dB,respectively.Thereturn
covering2.1GHzto7GHz(Figure3(a))andRFswitches.The lossandbandwidthofproposedprototypeTMAAatboththe
antenna, power divider, and RF switch are optimized using frequenciesaretabulatedinTable2.
EM simulator and CST microwave studio and tested using Firstly,theontimeduration(𝜏𝑛)andswitch-oninstance
theNetworkAnalyzerE5071CofAgilentTechnologies.The (𝑡on) of the rectangular pulses applied to RF switches are
prototypeofthepowerdividerisfabricatedandthescattering optimizedusingDEinordertoobtainradiationpatternwith
parametersarepresentedinFigure3.Figure3(b)showsthat suppressedSLLandenhanceddynamicefficiencyatboththe
the magnitude of 𝑆21 and 𝑆31 is marginally deviated from operating frequencies. To achieve 𝜂 ≥ 98%, the optimized
−3dB ensuring almost equal power division at 2.45GHz. timesequencesoftheinputpulsetrainaresetat𝜏1 =0.6035,
However itbecomesalmost−4.5dBat 5.8GHz. Figure3(c) 𝜏2 = 0.2548, 𝑡01 = 0, and 𝑡02 = 0.1226 using programmed
presentsasmallphasedifferencebetweenport2andport3 CPLDtomodulatetheinputexcitationaccordingto(7).The
overthebandwidthandensuresalmostequalpowersplitting. radiation pattern obtainedusing time modulated excitation
The structure of front and the back side of the broadband distribution is shown in the corresponding contour and
powerdividerisidenticalallowingequalcurrentdistribution CartesianplotgiveninFigures6,7,8,and9at2.45GHzand
atbothsides.Thedimensionsofthegroundplane,𝑑and𝐺ℎ, 5.8GHz,respectively.TheDEoptimizedsimulatedradiation
and the gap 𝑔 between the two arms of the bottom ground patterns,presentedinFigures8and9,confirmthattheSBL
10 InternationalJournalofAntennasandPropagation
Table2:Resultsofproposedprototypeantennaarray.
Prototype Frequency Parameter Simulatedvalue Measuredvalue
2.5GHz 𝑆11 −25.28dB −20.2dB
Bandwidth 1.21GHz 1.2GHz
ProposedarrayoftwoprinteddipoleswithU-shapedground
5.8GHz 𝑆11 −19.33dB −16.99dB
Bandwidth 1.11GHz 1.02GHz
Table3:DesiredandobtainedSLL. References
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