Corporate-FeedMultilayerBow-TieAntennaArray...

Hindawi Publishing CorporationModelling and Simulation in EngineeringVolume 2012, Article ID 327901, 8 pagesdoi:10.1155/2012/327901

Research Article

Corporate-Feed Multilayer Bow-Tie Antenna ArrayDesign Using a Simple Transmission Line Model

S. Didouh, M. Abri, and F. T. Bendimerad

Telecommunications Laboratory, Faculty of Technology, Abou-Bekr Belkaid University, 13000 Tlemcen, Algeria

Correspondence should be addressed to M. Abri, [email protected]

Received 16 April 2012; Revised 16 October 2012; Accepted 9 November 2012

Academic Editor: S. Taib

Copyright © 2012 S. Didouh et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

A transmission line model is used to design corporate-fed multilayered bow-tie antennas arrays; the simulated antennas arraysare designed to resonate at the frequencies 2.4 GHz, 5 GHz, and 8 GHz corresponding to RFID, WIFI, and radars applications.The contribution of this paper consists of modeling multilayer bow-tie antenna array fed through an aperture using transmissionline model. The transmission line model is simple and precise and allows taking into account the whole geometrical, electrical,and technological characteristics of the antennas arrays. The proposed transmission line model showed its interest in thedesign of different multilayered bow-tie antennas and predicted the correct resonance frequency for different applications intelecommunications. To validate the proposed transmission line model, the simulation results obtained are compared withthose obtained by the method of moments. The results of simulations are presented and discussed. Using this transmissionline approach, the resonant frequency, input impedance, and return loss can be determined simultaneously. The paper reportsseveral simulation results that confirm the validity of the developed model. The obtained results are then presented anddiscussed.

1. Introduction

Microstrip antenna arrays are exploited in a vast number ofengineering applications due to their ease of manufacturing,low cost, low profile, and light weight [1, 2].

Antenna arrays are used to scan the beam of an antennasystem, increase the directivity, and perform various otherfunctions which would be difficult with any single element.In the microstrip array, elements can be fed by a single lineor by multiple lines in a feed network arrangement. Based ontheir feeding method [3–5] the array is classified in series-feed network or corporate-feed network.

Corporate-feed network is general and versatile becauseit offers the designer more freedom in controlling the feedof each element (amplitude and phase). Although it leads toperformance degradation due to radiation, its constructionalsimplicity and low cost are still considered. This method hasmore control of the feed of each element and is ideal forscanning phased arrays, multiband arrays. Thus it providesbetter directivity as well as radiation efficiency and reducesthe beam fluctuations over a band of frequencies compared

to the series-feed array. The corporate-feed network is usedto provide power splits of 2n (i.e., n = 2, 4, 8, 16, etc.). This isaccomplished by using either tapered lines or using quarterwavelength impedance transformers.

In this paper, a transmission line model is used to designcorporate-feed multilayer antennas arrays to resonate at thefrequencies of 2.4 GHz, 5 GHz, and 8 GHz corresponding toRFID, WIFI, and radars applications, and the patches chosenas radiating elements for these arrays are in the bow-tieshape. The obtained simulation results are compared withthose obtained by the moment’s method (MoM).

2. Transmission Line Model Analysis

The preferred models for the analysis of microstrip patchantennas are the transmission line model, cavity model,and full wave model (which include primarily integralequations/Moment Method). The transmission line model isthe simplest of all and it gives good physical insight, but it isless accurate.

2 Modelling and Simulation in Engineering

(a)

LΔL ΔL

W2W1

(b)

Figure 1: Bow-tie antenna and its effective length.

Patch antenna

Aperture

Feed line

Substrate 1

Ground plane

Substrate 2

Figure 2: Configuration of bow-tie antenna fed by aperture coupled.

MLEFTL10Subst = “MSub2”

TFTF12

MLINTL48Subst = “MSub2”

TFTF11


MLINTL45

RR16

CC14C

C

TermTerm1

Z = 50 OhmNum = 1


CC15

RR15

MTAPERTaper12Subst = “MSub1” Subst = “MSub1”

MTAPERTaper11Subst = “MSub1”

W = ammL = dl mm

W = ammL = dl mm

L = c mm

R = rr OhmR = rr Ohm

T = 1

T = 1

W1 = ammW2 = bmm

L = c mm

W1 = ammW2 = bmm

W = wap mmL = lap mm

MLINTL49Subst = “MSub2”W = wap mmL = lap mm

L = lf mmW = wf mm W = ws mm

L = ls mm−

+

Figure 3: Equivalent circuit of the proposed antenna.

Modelling and Simulation in Engineering 3

287.1 mm

42 m

m

42.4 mm

30 mm

SMA connector

22.6 mm

Figure 4: Mask of the multilayered bow-tie antenna array operating at the frequency 2.4 GHz.

1.7 1.9 2.1 2.3 2.5 2.7 2.91.5 3

−15

−10

−5

−20

0

Frequency (GHz)

Proposed modelMomentum software

S 11

(dB

)

Figure 5: Simulated input antenna array return loss.

1.7 1.9 2.1 2.3 2.5 2.7 2.91.5 3

−100

0

100

−200

200

Frequency (GHz)

Proposed modelMomentum Software

Ph

ase

(◦)

Figure 6: Reflected phase at the antenna array input.

In this study, six bow-tie microstrip radiating elementsare used to design the corporate-fed array antenna. A bow-tie microstrip radiating patch which is shown in Figure 1 canbe considered as an open-ended transmission line of lengthL and width W .


Frequency (GHz)

Figure 7: Smith’s chart of the input impedance return losses.

1.7 1.9 2.1 2.3 2.5 2.7 2.91.5 3

3

5

7

9

1

10

Frequency (GHz)

VSW

R


Figure 8: Bow-tie antennas array VSWR.


31 m

m

20.1 mm

SMA connector

7.4 mm

2.5 mm

127.7 mm

Figure 9: Mask of the multilayered bow-tie antenna array operating at the frequency 5 GHz.

3. Microstrip Corporated-Feed Array Antenna

The printed array to be considered is one using aperture-coupled bow-tie microstrip patches. The aperture-coupledpatch element [4, 6] consists of two substrates, with a groundplane in between. As shown in the geometry for a singleaperture-coupled patch in Figure 2, a microstrip feed lineis printed on the bottom (feed) substrate, while the patchelement is printed on the top (antenna) substrate. Couplingbetween the feed line and the radiating element is through asmall slot in the ground plane below the patch.

The proposed transmission line equivalent circuit for anaperture coupled bow-tie antennas fed via microstrip line isshown in Figure 3.

In this equivalent circuit, two ideal transformers areassumed between the slot ground plane and both sides ofthe line. The energy is transferred and stored in these twotransformers in terms of load susceptance. In fact, all theenergy passes the slot aperture and delivers to the patchfor radiating. The ratios of these two transformers can bedetermined using [4]:

n1 =Lap

L, (1)

where Lap is the length of the slot.

While the second transformation ratio n2 can be approx-imated by the expression:

n2 =Lap√W · h , (2)

where h is the thickness of the substrate, the capacitance C iscalculated using the following equation as in [7]:

C(ε) = ε0εrA

hγnγm+

12γn

(εreff (εr ,h,W)

c0Z(εr = 1,h,W)

)− ε0εrA

h, (3)

γj ={

1, j = 0

2, j /= 0.(4)

4. Results and Discussions

The validity of the suggested model is highlighted bycomparing the results of the return loss, the input phase,input antenna VSWR, and input impedance locus to thoseobtained by the moment’s method of the MomentumSoftware. The simulated antennas arrays are designed toresonate, respectively, at the frequencies 2.4 GHz and 8 GHz.

4.1. Bow-Tie Antenna Array Operating at the Resonant Freq-uency 2.4 GHz. The configuration of the proposed arrayis shown in Figure 4, which consists of 6 identical bow-tie patch elements in parallel or corporate feed to cover2.4 GHz operating frequency. The corporate feed has a singleinput port and multiple feed lines in parallel constitutingthe output ports. Each of these feed lines terminates at anindividual radiating element and therefore transfers all itsenergy into the element.

The antenna array is to be designed on substrate whichhas a relative permittivity εr of 2.54, a dielectric thickness hof 1.6 mm, and a loss tangent of about 0,019 and 0.05 mmconductor thickness. A rectangular slot with Lap = 26 mmand width Wap = 2.6 mm is used for coupling the patch to amicrostrip line of length L f = 20 mm, etched on substratewhich has a relative permittivity εr of 2.54, a dielectric


4.7 4.9 5.14.5 5.3

−15

−10

−5

−20

0

Frequency (GHz)

Proposed modelMomentum Software

S 11

(dB

)


4.7 4.9 5.14.5 5.3

−100

0

100

−200

200

Frequency (GHz)


Ph

ase

(◦)

Figure 11: The antenna array input-reflected phase.

thickness h of 1.6 mm, and a loss tangent of about 0.019 and0.05 mm conductor thickness.

The mask of the multilayer bow-tie antenna array withdimensions is shown in Figure 4.

The simulated input return loss of multilayer bow-tieantenna array is displayed at the frequency 2.4 GHz inFigure 5.

The representation of the reflection coefficient as a func-tion of the resonance frequency is shown by the appearanceof several resonance frequencies, which is a characteristic ofthe multiband antenna array.

The results show the appearance of a resonant modeat the frequency 2.4 GHz and a good agreement by theproposed model and the Momentum software. It appearsthat a peak of −17.52 dB using transmission line model witha light shift by the moment method provides a return loss of−11.24 dB at the frequency 2.42 GHz.

The moments results and those obtained from transmis-sion line model of the input phase of return loss for thisantenna array are shown in Figure 6.

From Figure 6, both models have the same shape and wenote very well that the phase is null by the two models at theresonant frequencies, which means a perfect adaptation.


Figure 12: Smith’s chart of the input impedance locus.

4.7 4.9 5.14.5 5.3

3

5

7

9

1

10

Frequency (GHz)

VSW

R


Figure 13: Bow-tie antenna array VSWR.

The impedance locus of the antennas array from 1.5 to3 GHz is illustrated on Smith’s chart in Figure 7.

It can be seen from Figure 7 that both models representthe locations of input impedances in a manner almostidentical; this justifies the good agreement between the twomodels.

From Figure 8, there is a good agreement between thetwo models; the level of VSWR is close to unity, implyinga good adaptation of the antenna array and precision of themodel line transmission.

4.2. Bow-Tie Antenna Array Operating at the Resonant Freq-uency 5 GHz. The selected configuration is shown inFigure 9 and consists of six bow-tie identical patches mul-tilayer operating at the resonant frequency 5 GHz.

The antenna array is to be designed on substrate whichhas a relative permittivity εr of 2.54, a dielectric thickness h


155.4 mm

21.6

5 m

m

24.13 mm

14.1 mm

SMA connector

10.29 mm

Figure 14: Mask of the multilayered bow-tie antenna array operating at the frequency 8 GHz.

of 1.6 mm, and a loss tangent of about 0,019 and 0.05 mmconductor thickness. A rectangular slot with Lap = 18 mmand width Wap = 0.6 mm is used for coupling the patch to amicrostrip line of length L f = 10 mm, etched on substratewhich has a relative permittivity εr of 2.54, a dielectricthickness h of 1.6 mm, and a loss tangent of about 0.019 and0.05 mm conductor thickness.

The multilayer bow-tie antenna array designed withdimensions in millimeter is represented in Figure 9.

The mask of the multilayer bow-tie antenna array withdimensions is shown in Figure 10.

From Figure 10, the resonance of antenna array iscorrectly predicted by both models to be 5 GHz, and asa result we note a peak of about −13.54 dB obtained bytransmission line model and of about −19.6 dB by themoment’s method.


The reflected phase is null by the two models in spite ofthe shift observed by transmission line model.

The input impedance locus of the multilayer bow-tieantenna array is illustrated on Smith’s chart in Figure 12.

It is observed that the curves of the two models passby the axis of 50Ω. The simulated VSWR is represented onFigure 13.

According to Figure 13, there is good agreement betweenthe two models (transmission line model and the momentmethod). Around the resonant frequency the VSWR is closeto unity implying a good adaptation of the network.

4.3. Bow-Tie Antenna Array Operating at the Resonant Freq-uency 8 GHz. In this section, other geometry is analyzed byusing the method proposed in this paper. The antenna array

7.9 8 8.17.8 8.2

−25

−20

−15

−10

−5

−30

0

Frequency (GHz)


S 11

(dB

)


consists of six bow-tie identical multilayer patches, as shownin Figure 14 and is designed to operate at 8 GHz frequency.

The antenna array is to be designed on substrate whichhas a relative permittivity εr of 2.54, a dielectric thickness hof 1.6 mm, and a loss tangent of about 0,019 and 0.05 mmconductor thickness. A rectangular slot with Lap = 16 mmand width Wap = 2.6 mm is used for coupling the microstripline of 10 mm length to the patch, etched on a substratewhich has a relative permittivity εr of 2.54, a dielectricthickness h of 1.6 mm, and a loss tangent of about 0,019 and0.05 mm conductor thickness.

Figure 14 presents the mask layout for multilayer bow-tieantenna array at the resonant frequency 8 GHz.

The simulated input return loss of multilayer bow-tie antenna array is displayed at the frequency 8 GHz inFigure 15.


7.9 8 8.17.8 8.2

−100

0

100

−200

200

Frequency (GHz)


Ph

ase

(◦)

Figure 16: The antenna array input-reflected phase.


Frequency (GHz)

Figure 17: Smith’s chart of the input impedance return losses.

From Figure 15, it is observed that the resonance of theantenna array is correctly predicted to 8 GHz by the twomodels. It shows a peak of−19.60 dB using transmission linemodel and a peak of 12.84 dB by the moment method.


As shown in Figure 16, a good agreement betweenthe transmission line model and moment’s method, thesimulation results also show that the phase is null by the twomodels.

The impedance locus of the multilayer bow-tie antennaarray is illustrated on Smith’s chart in Figure 17.

The input impedance or the antenna has been calculatedover a frequency range of 7.8–8.2 GHz. It can be seen from

7.9 8 8.17.8 8.2

3

5

7

9

1

10

Frequency (GHz)

VSW

R


Figure 18: Bow-tie antenna array VSWR.

Table 1: Comparison between transmission line model and methodof moments.

Antennasarrays

ModelReturn

loss(dB)

Resonantfrequency

(GHz)

Frequencyshift(%)

2.4 GHz (RFID)MLT −17.52 2.4

MoM −11.24 2.420.8%

5 GHz (WIFI)MLT −13.54 5

MoM −19.60 5.010.2%

8 GHz (RADAR)MLT −19.60 8

MoM −12.84 80%

Figure 17 that the curves of the two models pass by the axisof 50Ω.

From Figure 18, in the vicinity of the resonant frequencythe VSWR is close to the unit which corresponds to an idealmatching.

To better illustrate the results obtained in terms ofadaptation, the comparison of the results in terms of returnloss and resonant frequency between the transmission linemodel (MLT) and the method of moments (MoM) issummarized in Table 1.

Table 1 shows that the largest amount of frequency shiftis produced by antenna 2.4 GHz which produced a resonancefrequency of 2.4 GHz by MLT and 2.42 GHz by MoM, a shiftof about 0.8% from 2.4 GHz. The lowest frequency shift isshown by antenna 8 GHz, a shift of about 0% from 8 GHz.

The return losses generated by all antennas arrays, whichare all in the magnitudes less than −11 dB, show that a goodimpedance matching has been achieved in both models.

5. Conclusion

In this paper three multilayered bow-tie antennas arrays havebeen designed, which consist of 6 identical bowtie patchelements in parallel or corporate feed to resonate at thefrequencies 2.4 GHz, 5 GHz, and 8 GHz corresponding toRFID, WIFI, and radars applications using an equivalentcircuit. The transmission line model can be successfully


used to design the corporate-fed multilayer bow-tie antennasarrays, and even though the model is conceptually simple,it still produces accurate results in a relatively short periodof computing time. The proposed transmission line modelshowed its interest in the design of different multilayeredbow-tie antennas arrays feed in parallel, predicting thecorrect resonance frequency for different applications intelecommunications. The results obtained highlighted agood agreement between the transmission line model andthe moment’s method. A comparison of the results producedby the final model with the moment’s method showed thevalidity of the proposed model.

References

[1] M. Abri, N. Boukli-hacene, and F. T. Bendimerad, “Appli-cation du recuit simule a la synthese d’antennes en reseauconstituees d’elements annulaires imprimes,” Annales DesTelecommunications, vol. 60, no. 11-12, pp. 1424–1440, 2005.

[2] G. Dubost, “Broadband circularly polarized flat antenna,” inProceedings of the International Symposium on Antennas andPropagat, pp. 89–92, Sendai, Japan, 1978.

[3] M. M. Alam, “Design and performance analysis of microstriparray antenna,” in Progress in Electromagnetic Research Sympo-sium Proceedings, Moscow, Russia, August 2009.

[4] M. Abri, N. Boukli-Hacene, and F. T. Bendimerad, “Weightedarray design of an aperture coupled printed antennas,” inProceedings of the Mosharaka Multi-Conference on Communi-cations, Signals and Control (MM-CSC ’07), Amman, Jordan,2007.

[5] M. F. Bendahmane, M. Abri, F. T. Bendimerad, and N. Boukli-Hacene, “A simple modified transmission line model for insetfed antenna design,” International Journal of Computer ScienceIssues, vol. 7, no. 5, pp. 331–335, 2010.

[6] M. Himdi, J. P. Daniel, and C. Terret, “Transmission lineanalysis of aperture-coupled microstrip antenna,” ElectronicsLetters, vol. 25, no. 18, pp. 1229–1230, 1989.

[7] C. A. Balanis, Antenna Engineering, Willey, 2nd edition, 1982.

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