Int. J. Electron. Commun. (AE) 66 (2012) 68 75

Contents lists available at ScienceDirect

International Journal of Electronics andCommunications (AE)

j our na l ho mepage: www.elsev ie

On the cta

Raj KumMicrowave and nstitutIndia

a r t i c l

Article history:Received 24 AAccepted 10 M

Keywords:Microstrip antFractalMonopole antUltrawide banCPW-FedResonant frequOmnidirection

ibed tric cxpercorrena hantenup deful fo

1. Introdu

The Fedethe 3.1 to 10.6 GHz band for UWB modern communications. Ultra-Wideband (UWB) commonly refers to signal or system that eitherhas a large relative bandwidth (BW) or a large absolute band-width [13]. Such a large BW offers specic advantages with respectto signal rosimplicity. Usmall size aare much mand multi-bnas investigprotruded scuits and tcircular disvarious UWapplicationproposed tonotched ulting stub is pDing et al. [fractal antecircular UW

This papantenna for

CorresponE-mail add

agesn, lotion

of antenna has been done. The performance of the proposedantenna is characterized in term of impedance bandwidth, radi-ation patterns and group delay.

1434-8411/$ doi:10.1016/j.bustness, information content and/or implementationWB communication system requires a UWB antenna of

nd simple to design and fabricate. Some UWB antennasore complex than other existing single band, dual bandand antennas [46]. Most of the UWB monopole anten-ated till today are non-planar as in [5,6] and due to theirtructure, they cannot be integrated with integrated cir-hey are fragile. Liang [7] has reported the CPW-feedc monopole antenna for UWB applications. Recently,B fractal antennas have also been reported for UWBs [811]. In [8], CrownSierpinski microstrip antenna is

reduce the size of a crown square fractal. The frequencyra-wideband microstrip slot antenna with a fractal tun-roposed to achieve frequency notched function [9,10].11] and Kumar et al. [12,13] have proposed a new UWBnna by adopting the fractal concept on the CPW-fedB antenna.er presents a new inscribed triangle circular fractal

UWB applications. The proposed fractal antenna has

ding author. Tel.: +91 20 24304149.ress: dr.rajkumarkumar@yahoo.com (R. Kumar).

2. Antenna geometry

Monopole antenna with CPW-feed of 30 mm diameter is shownin Fig. 1a. This is called as initiator or zeroth iteration. Fractalgeometry with each iteration has been constructed from monopolecircular disc of 30 mm diameter. In rst ietration, four regular poly-hedron of size 8.57 mm has been taken inside the circle of diameter30 mm and each polyhedron is rotated with an angle 30. Thesefour polyhedron were substrated from 30 mm circle diameter. Thisis called 1st iteration as shown in Fig. 1b. In 2nd iteration, a circleof 21.2 mm diameter has been taken inside this four polyhedron. In21.2 mm diameter circle, four polyheron of size 8.53 mm has beentaken again and each polyheron is rotated with an angle of 30 thenthis four polyheron were substrated from 21.2 mm circle diameter.This is called 2nd iteration as shown in Fig. 1c. In 3rd iteration,a circle of 15 mm diameter has been taken inside the substratedpolyheron. In this circle of diameter 15 mm again four polyheronof size 8.5 mm has been taken and each polyheron is rotated withan angle of 30 then these four polyheron were substrated from15 mm circle diameter. This is called 3rd iteration as shown inFig. 1d. In 4th iteration, a circle of 10.7 mm diameter has been takeninside the substrated four polyheron. Now, in this circle of diameter10.7 mm again four polyheron of size 8.46 mm has been taken each

see front matter 2011 Elsevier GmbH. All rights reserved.aeue.2011.05.003 design of inscribed triangle circular fra

ar , Dhananjay Magar, K. Kailas Sawant Millimeterwave Antenna Laboratory, Department of Electronics Engineering, Defence I

e i n f o

pril 2010ay 2011

enna

ennadwidth

encyal radiation pattern

a b s t r a c t

In this article, an ultrawide band inscrbeen designed on FR4 substrate dielecdimension of 30 mm diameter. The ebandwidth from 2.25 GHz to 15 GHz ultrawide band characteristcs of antenmeasured radiation pattern of fractal ain elevation plane. The measured groband. Such type of antenna is very us

ction

ral Communications Commission (FCC) has designated

advantricatiointegrar .de /a eue

l antenna for UWB applications

e of Advanced Technology (Deemed University), Girinagar, Pune 411025,

triangle circular fractal antenna is presented. The antenna hasonstant r = 4.3 and thickness of substrate 1.53 mm with initialimental result of fractal antenna exhibits the excellent ultrasponds to 147.83% impedance bandwidth at VSWR 2:1. Thiss been achieved by using the CPW-fed and fractal concept. Thena is nealy omnidirectional in azimuth plane and bidirectionalelay of proposed antenna is almost constant throughout ther UWB communication system.

2011 Elsevier GmbH. All rights reserved.

of compact size, low manufacturing cost, easy fab-w prole, and very small ground plane suitable for

with compact UWB systems. A detail parametric study

R. Kumar et al. / Int. J. Electron. Commun. (AE) 66 (2012) 68 75 69

to each iteration.

polyheron idron were s4th iteratioinnite itersible becauantenna hatric constanantenna asalso been fating elemFR-4 substrtan = 0.022

3. Design o

The desicalculating

fr = 1.8412reff

where vo iscalculated b

reff = ro

[1 +

where rsimple solihas been deand thickneantenna hasnar feed is telements areported [1respect of b

4. UWB ch

A simplein Fig. 1a. Itantenna is mcurrent denmonopole adle area of In this waylonger. In increased bthe rst rethe antennthe fractal quency in h

r disc monopole antenna. In this paper, resonance elementseen added by inscribing polyhedron in various concentric

as shown in Fig. 1. The proposed fractal antenna with opti- dimension has been shown in Fig. 2 with CPW-feed. The

pedance is achieved by adjusting the width W = 3.2 mm ofer conductor and the gap between the ground plane andidth is g1 = 0.5 mm. To achieve the UWB characteristic, thetween patch and ground has been optimized to h = 0.4 mm.ngth of ground plane GL = 28 mm and width of the ground5 mm have been optimized.

ametic study of fractal antenna

circular disc monopole fractal antenna has been shown 2 with optimized dimension. It has been observed duringtion that the UWB characteristic of the proposed antennaFig. 1. Proposed antenna with respect

s rotated with an angle of 30 then these four polyhe-ubstrated from 10.7 mm circle diameter. This is calledn as shown in Fig. 1e. This process can be repeated uptoation. Practically innite iterative structure is not pos-se of fabrication constraints. The fourth iterative fractals been nalized to design on the same substrate dielec-t and thickness as conventional microstrip monopole

shown in Fig. 1a. This fourth iterative antenna hased with the coplanar feed. The CPW-feed and radi-ents both are printed on the top side of a low-costate with dielectric constant r = 4.3, h = 1.53 mm and1.

f circular microstrip antenna

gn expression of simple circular microstrip antenna forthe resonant frequency [14] is given as

voeff

(1)

the velocity of light. The effective radius reff can bey following expression

2h

roeff{

ln(

ro2h

)+ (1.41r + 1.77) + hro (0.268eff + 1.65)

}]1/2

(2)

o is radius of the circular patch. The dimension of thed circular patch is taken as radius 15 mm. This patchsigned on FR4 substrate dielectric constant of r = 4.3ss h = 1.53 mm. The monopole and fractal monopole

been fed with 50 CPW-feed. The advantage of copla-hat the feed of the antenna, ground plane and radiatingll are printed on the same side of the substrate. It has113] that CPW-feed antenna performs better well inandwidth and the radiation pattern.

aracteristic and miniaturization

circular disc monopole antenna with CPW-fed is shown is understood that current distribution of the proposed

circulahave bcirclesmized50 imthe innfeed wgap beThe leplane 2

5. Par

Thein Fig.simulaainly along the circumference of the circular disc. Thesity is low in the middle area of the solid circular discntenna. Therefore, the current will not effect if the mid-the solid circular disc monopole antenna is removed., the effective path of the surface current will becomethis antenna, the effective length of current path isy inscribing triangle in solid circular disc. This resulted,sonance frequency will be decreased and the size ofa will be reduced. To achieve the UWB characteristic,structure can be added to increase the resonance fre-igh frequencies by adding resonance elements in solid Fig. 2. Proposed fractal antenna with coplanar feed.

70 R. Kumar et al. / Int. J. Electron. Commun. (AE) 66 (2012) 68 75

Fig. 3. Simulated results of proposed fractal antenna with respect to each iteration.

is heavily dependent on the iteration number, gap betweenpatch and ground, gap between feed and ground, ground length,ground width and the diameter of the circular disc. So theseparameters of antennas should be optimized for maximum band-width.

5.1. Effect o

First, antion, i.e. forof these iteresult, the ing throughantenna, thband is imantennas, thiterative frathe band.

5.2. Effect of gap between patch and ground

It is noticed that current density is mainly distributed on theupper edge of ground plane and along the edge of circular disc,which reveals that gap between patch and ground has a role on

ancoundne tofract

of gated reen effecrom ncy ire isgap (n fab

= 0.5f each iteration

tenna has been simulated with respect to each itera- 1st, 2nd, 3rd and 4th iteration. The simulated resultsrations are shown in Fig. 3. It is clear in simulatedrst iterative antenna gives the poor impedance match-out the band. It is also observed for second iterativee impedance matching over the operating frequencyproved drastically. For the third and fourth iterativee impedance matching is further improved. The fourthctal antenna gives the impedance matching throughout

performand grfeed liposed valuessimulaIt has bpatch clear ffrequeSo, themized has beeand g1Fig. 4. Simulated results of proposed fractal antenna for various gap (e of the antenna. This parameter, i.e. gap between patch plane (h) has been optimized for proper coupling from

patch which effects the UWB characteristic. The pro-al monopole antenna has been simulated for variousp from 0.3 mm to 0.6 mm with the step of 0.1 mm. Theesults have been shown in Fig. 4 for these values of gap.observed from results that gap (h) between ground andts the lower end frequency and bandwidth. It is alsothe simulated results, as the gap h decreases, low ends almost constant but the high end frequency increases.

evident increase in the BW as gap decreases. The opti-h) is achieved h = 0.4 mm. The proposed fractal antennaricated with gap h = 0.4 mm, 50 feed with W = 3.2 mm

mm.h) between patch and ground plane.

R. Kumar et al. / Int. J. Electron. Commun. (AE) 66 (2012) 68 75 71

Fig. 5. Simulated results of proposed fractal for various gap (g1) between feed width and ground plane.

5.2.1. Effect of the gap between feed and groundThe gap between the feed width and ground is also important

for proper impedance ulated for v(g1). The sigap is clearing through0.3 mm to 0gap has beefor optimizthe optimizg1 = 0.5 mm

5.3. Effect o

Other thespecially t

affecting the antenna impedance and consequently the BW. Largelength of ground plane means longer CPW-feed line. In monopole

a ther diaious he siter, id. In68 mono

cularr wa

fect o

e, thole aa bamatching. Because, variation of gap effects the inputof antenna. The proposed fractal antenna has been sim-arious value of the gap between feed and ground planemulated results are shown in Fig. 5. The effect of thely visible in the simulated results. The proper match-out the band is achieved by optimizing the gap from.7 mm with the step of 0.1 mm. The optimum value ofn achieved 0.5 mm. Initially value of feed width and gapation have been taken W = 3.2 mm and g1 = 0.3 mm. Ination, these values have been achieved W = 3.2 mm and.

f the ground plane length

an this, we have also seen that the ground plane sizehe length of the ground plane is also an important factor

antenncirculafor varfrom tdiamethe banto 34.3of the mple cirquarte

5.4. Ef

HermonopantennFig. 6. Simulated result of proposed fractal antenna for v ground length should be around /4 or nearly equal tometer. The effect of ground length has been simulatedvalue of ground length as shown in Fig. 6. It is observedmulated results as the length approaches near to thet gives the good impedance matching the throughout

optimization ground length is varied from 28.364 mmm with the step of 2.0 mm. The rst resonant frequencypole antenna is determined by the diameter of the sim-

disc. For simple circular disc antenna, it behaves like ave monopole antenna.

f the ground plane width

e width of the ground plane of proposed fractalntenna has also been optimized and its effect on thendwidth is observed. The proposed antenna has beenarious ground length.

72 R. Kumar et al. / Int. J. Electron. Commun. (AE) 66 (2012) 68 75

Fig. 7. Simulated result of proposed fractal antenna for various ground width.

simulated for various ground plane width (GW) from 24.9 mm to39.9 mm with step of 5.0 mm. The simulated results with respectto various ground width (GW) are shown in Fig. 7. It is observedas the ground width increases the rst resonant frequency shiftedto lower frequency side. For proper matching and compact size ofantenna, the optimum ground width is achieved 25 mm by xingall others optimized parameters.

5.5. Effect of the diameter of circular disc

From Figalong the ednant frequeHere the efbeen simulmental retu18.4 mm, 30has been shthe rst res

The proposed fractal antenna has been constructed with 30 mmdiameter of circular disc.

6. Experimental results

The proposed inscribed triangle circular fractal antenna isshown in Fig. 2 with optimized dimension. The all iterativeinscribed triangle circular fractal antenna has been fabricated and

The, thi

= 0.5rk annten

in Fe ane anthirdes fu. 2, again reveals that the current is mainly distributedge of the circular disc. This indicates that the rst reso-ncy is associated with the diameter of the circular disc.fect of the dimension of the circular disc diameter hasated as well as experimentally measured. The experi-rn loss versus frequency for various diameter 15 mm,

mm and 80 mm of the circular disc monopole antennaown in Fig. 8. As the diameter of circular disc increases,onant frequency shifted towards lower frequency side.

tested.r = 4.3and g1netwoative ashowniterativiterativIn the improvFig. 8. Experimental results of simple circular disc monopole antenna for 80 se iterative antennas have been designed on substrateckness 1.53 mm, GL = 28 mm, GW = 25 mm, h = 0.4 mm

mm. These antennas have been tested using vectoralyzer R&S ZVA 40. The experimental results of all iter-nas have combined using vector network analyzer asig. 9. It is observed from experimental results that 1sttenna offers very poor impedance bandwidth. In 2ndtenna, the impedance bandwidth improves drastically.

and fourth iterative antennas, impedance bandwidthrther throughout the band. The experimental resultsmm, 30 mm 18.4 mm and 15 mm diameter.

R. Kumar et al. / Int. J. Electron. Commun. (AE) 66 (2012) 68 75 73

Fig. 9. Experimental results of each iterative antenna and simulated result of proposed antenna.

of proposed fractal antenna exhibits the excellent ultra wideimpedance bandwidth of 12.75 GHz (from 2.25 GHz to 15 GHz) cor-responds to 147.83% impedance bandwidth at VSWR 2:1. The mea-sured returshown in Fiof Ultra widThe simulaiteration armental andtion. This mof the thicklower qualithe substra

The peaposed antenare shown i

5 dBi throughout the FCC band (3.110.6 GHz). It is also observedthat radiation efciency of the antenna decreases as the frequencyincreases. This is due to the high loss tangent tan = 0.0221 of the

ate.

erim

iatioa haa muthes 3. Tht vaz a

tternn loss versus frequency of this fractal antenna has beeng. 9. This antenna satises the bandwidth requiremente band communication system, i.e. from 3.1 to 10.6 GHz.ted results of proposed antenna with respect to eache shown in Fig, 3. A good agreement between experi-

simulated results is observed except some slight varia-ay be due to the tolerance in manufacturing, uncertaintyness and/or the dielectric constant of the substrate andty of SMA connector (VSWR = 1.3), larger tan = 0.02 ofte and soldering effects of an SMA connector.k gain, directivity and radiation efciency of the pro-na are simulated using HFSS10. The simulated resultsn Fig. 10. It is observed peak gain of antenna is less than

substr

7. Exp

Radantennantennin azimquenciFig. 11sured a10.2 GHtion paFig. 10. Simulated peak gain, directivity and radiation efciency oental radiation patterns

n characteristics of the inscribed triangle fractalve been measured in in-house anechoic chamber usingeasurement system. The measured radiation patterns

plane (H-plane) have been calculated at selective fre-.0 GHz, 4.275 GHz, 6.3 GHz and 10.2 GHz as shown ine radiation patterns in E-plane have also been mea-rious selective frequencies 3.0 GHz, 4.275 GHz, 6.3 GHz,nd 11.2 GHz as shown in Fig. 12. The H-plane radia-s are almost omnidirectional, and the E-plane radiationf the proposed fractal antenna.

74 R. Kumar et al. / Int. J. Electron. Commun. (AE) 66 (2012) 68 75

Fig. 11. H-plane experimental radiation patterns of proposed fractal antenna atfrequencies 3.0 GHz, 4.275 GHz, 6.3 GHz and 10.2 GHz.

patterns are nearly bidirectional. It can be seen that the radiationpatterns offrequency rcies 4.125 Gshown in Fratio at 4.114.56 GHz. Trequiremen10.6 GHz. Itfrequency ruseful for U

Fig. 12. E-plafrequencies 3 G

Fig. 13. Experimental cross polarization of proposed fractal antenna at frequencies4.125 GHz, 6.525 GHz and 10.5 GHz.

8. Group d

The groues a e gro

f

is grouwo fa

putred gn in

e quiB c the proposed antenna are stable over the operatingange. The experimental cross polarization at frequen-Hz, 6.525 GHz and 10.5 GHz has been measured asig. 13. It has been observed cross to co polarization25 GHz is better than 15 dBi and reduces to 5 dBi athe proposed antenna gain in operating band meets thet for FCC dened UWB frequency band from 3.1 GHz to

has been observed that antenna gain is less than 5 dBi inange 3.1 GHz to 10.6 GHz. Such type of antenna is veryWB communication system.

indicatity. Th

g = 2where

Theusing tnas aremeasuas showprovidern UWne experimental radiation patterns of proposed fractal antenna atHz, 4.275 GHz, 6.3 GHz, 10.2 GHz and 11.2 GHz. Felay of antenna

p delay is an important parameter for UWB system. Itquantity of a pulse distortion and far-eld phase linear-up delay is dened as

the far-eld phase and f is frequency.p delay of proposed fractal antenna has been measuredbricated identical antennas. These two identical anten-

face to face at distance 30 cm as shown in Fig. 14. Theroup delay is nearly constant throughout the pass band

Fig. 15. It indicates that proposed fractal antenna cante good pulse-handling capability as demanded by mod-ommunication systems. Such type of antenna is veryig. 14. Experimental set up to measure the group delay.

R. Kumar et al. / Int. J. Electron. Commun. (AE) 66 (2012) 68 75 75

ed fra

useful for Uprecision p

9. Conclus

In this ptal antennaThe propostics from 2the radiatioand bidirecThe measurconstant thclose agreeantenna is bandwidth coplanar grable for theuseful for Ucommercia

Acknowled

AuthorsInstitute of for permittreviewers f

nces

antz H5.llo GRgazinen B, ear an

ng J, C ultra pagatawallnsactimouFig. 15. Measured group delay of propos

WB communication system, microwave imaging andositioning system.

ions

aper, a novel CPW-feed inscribed triangle circular frac- has been proposed and implemented experimentally.ed monopole fractal antenna offers UWB characteris-.25 GHz to 15 GHz at VSWR 2:1. It is observed thatn patterns of antenna are omnidirectional in H-planetional in E-plane over the entire operating bandwidth.

Refere

[1] Sch200

[2] AieMa

[3] AlleRad

[4] LiaforPro

[5] AgrTra

[6] Ham

ed group delay of proposed fractal antenna is almostroughout the band. The measurement results are inment with the simulation results. The proposed fractalcompact, low prole, and offers very large impedancerequired for next generation UWB system. The use ofound plane makes the design conformal and more suit-

miniaturized applications. Such type of antenna can beWB system as well as suitable for various military andl wideband applications.

gements

are grateful to the VC and Pro-VC and Dean of DefenceAdvanced Technology (Deemed University), Pune, Indiaing to publish this work. Author is also thankful to theor suggestion to improve the manuscript.

band disc[7] Liang J, G

UWB app[8] Dehkhod

and Prop[9] Lui VJ, C

microstri2005;41:

[10] Lui WJ, Cprinted s2006;16:

[11] Ding M, JiMicrowa

[12] Kumar ROptical T

[13] Kumar Rfor UWB (5)):1079

[14] Verma Acircular 2002;2(Dctal antenna.

. The Art and Science of Ultra wideband Antennas. Artech House Inc.;

, Rogerson GD. Ultra-wideband wireless systems. IEEE Microwave 2003;(June):3647.t al. Ultra-Wideband Antennas and Propagation for Communications,d Imaging. John Wiley & Sons; 2007.hiau C, Chen X, Yu J. Study of a circular disc monopole antennaswideband applications. International Symposium on Antennas andion 2004;(August):1721.

NP, Kumar G, Ray KP. Wide-band planar monopole antennas. IEEEons on Antennas and Propagation 1998;46(February (2)):2945.d M, Poey P, Colombel F. Matching the input impedance of a broad- monopole. Electronics Letters 1993;29(February (4)):4067.uo L, Chiau CC, Chen X. CPW-fed circular disc monopole antenna forlications. IEEE AP-S 2005:5058.

P, Tavakoli A. A crown square microstrip fractal antenna. IEEE Antennaagation Society Symp Dig 3 2004:23969.heng CH, Cheng Y, Zhu H. Frequency notched ultra-widebandp slot antenna with fractal tuning stub. Electronics Letters2946.heng CH, Zhu HB. Compact frequency notched ultra-wideband fractallot antenna. IEEE Microwave Theory and Wireless Component Letters2246.n R, Geng J, Wu Q. Design of a CPW-fed ultra wideband fractal antenna.ve and Optical Technology Letters 2007;49:1736., et al. On the design of wheel shape fractal antenna. Microwave andechnology Letters 2011;53(January (1)):1559., et al. Design of CPW-feed inscribed square circular fractal antennaapplications. Microwave and Optical Technology Letters 2011;53(May83.K, Nasimuddin. Simple accurate expression for directivity ofmicrostrip antenna. Journal of Microwaves and Optoelectronicsecember (6)).

On the design of inscribed triangle circular fractal antenna for UWB applications1 Introduction2 Antenna geometry3 Design of circular microstrip antenna4 UWB characteristic and miniaturization5 Parametic study of fractal antenna5.1 Effect of each iteration5.2 Effect of gap between patch and ground5.2.1 Effect of the gap between feed and ground

5.3 Effect of the ground plane length5.4 Effect of the ground plane width5.5 Effect of the diameter of circular disc

6 Experimental results7 Experimental radiation patterns8 Group delay of antenna9 ConclusionsAcknowledgementsReferences