Int. J. Signal and Imaging Systems Engineering, Vol. 6, No. 1, 2013 9

ACS fed koch fractal antenna for wide-band

applications

Yogesh Kumar Choukiker*

and Santanu Kumar Behera

Department of Electronicsand Communication Engineering,National Institute of Technology, RourkelaRourkela 769008, IndiaE-mail: yogesh.ku.84@gmail.comE-mail: skbehera@ieee.org*Corresponding author

Abstract: A compact Asymmetric Coplanar Strip (ACS) feed modified Koch fractal shapeprinted slot antenna is presented in this paper. It is suitable for Wireless, WiMax, WiBroand other important frequencies. Here, the operating frequencies of the triangular slotantenna are lowered by the Koch iterations technique resulting in compact antenna.The proposed antenna exhibits wideband frequency response. The simulated –10 dBbandwidth for this resonant frequency is 97.7% in the range of 2.7–7.88 GHz. The antennaexhibit omnidirectional radiation pattern with ≤3 dBi gain for entire band. Parametric studyof different antenna is presented and discussed in this paper.

Keywords: ACS feed; fractal Koch antenna; wideband.

Reference to this paper should be made as follows: Choukiker, Y.K. and Behera, S.K. (2013)‘ACS fed koch fractal antenna for wide-band applications’, Int. J. Signal and ImagingSystems Engineering, Vol. 6, No. 1, pp.9–15.

Biographical notes: Yogesh Kumar Choukiker received the BE Degree in Electronicsand Communication Engineering from Rajiv Gandhi Technical University, Bhopal, Indiain year 2007 and MTech in Telematics and Signal Processing from National Instituteof Technology, Rourkela, India in the year 2009. Currently he is pursuing PhD inthe Department of Electronics and Communication, National Institute of Technology,Rourkela, India. His areas of interest are Microwave, Microstrip Antenna, Fractal Antennaand Optimisation Techniques. He is a Student Member of IEEE (USA).

Santanu K. Behera received the BSc (Engg) Degree from UCE Burla, SambalpurUniversity in the year 1990, ME and PhD (Engg) from Jadavpur University in theyear 2001 and 2008 respectively. He is presently working as an Associate Professorin the Department of Electronics and Communication Engineering, National Instituteof Technology Rourkela, India. His current research interests include planar antenna,dielectric resonator antenna and metamaterials. He is a Life Member of IETE (India),Computer Society of India, Society of EMC Engineers (India), ISTE (India) and Memberof IEEE (USA). He is a reviewer for ICTACT Journal of Communication Technology,India.

1 Introduction

Rapid progress in wireless communication promisesto replace wired communication in the near future,in which antenna plays an important role. Microstrippatch antenna are widely used due to their inherentadvantages of low profile, light weight, low cost (Jamesand Hall, 1989; Chang, 1989; Pozar and Schaubert, 1995;Kumar and Ray, 2003) etc. The major limitation ofmicrostrip antenna is narrow bandwidth. To overcomethis limitation the patches are etched with slot like

E-Shape (Yang et al., 2001), U-Shape (Lee et al., 1997),and Stack patch (Sappan, 1991). But using this type ofshape the boundary condition and the cavity model areinvalid for design and analysis.

Printed slot antennae are attractive because oftheir planar geometry and wide operating bands(Kahrizi et al., 1993). A coplanar waveguide (CPW)feed makes them more suitable for compact wirelesscommunication devices owing to its features likeuniplanar structure, easy fabrication and circuitintegration (Chen and Chen, 2004). Compact antenna

Copyright © 2013 Inderscience Enterprises Ltd.

10 Y.K. Choukiker and S.K. Behera

can be designed using a meandered radiating structureand several antenna using this technique has beenreported (Chen, 2002; Liu and Chen, 2004).

Fractal antennae (Werner and Mittra, 1999), havevery good features like small size and multibandcharacteristics. Most fractal objects have self similarshapes, with different scale factors (Jones et al., 1990;Mandelbort, 1983). The most common fractal in thecategory of fractal antenna is presented for variouswireless applications (Choukiker and Behera, 2010a,2010b). The fractal shape carried out by applying theinfinite number of iterations using Multiple ReductionCopy Machine (MRCM) algorithm (Peitgen, 1990). Inthis paper, ACS feeding is employed for designinga compact fractal Koch shape antenna for widebandapplication.

In this paper, we proposed the modified fractalKoch antenna with triangular shape for widebandapplication. This is a simple model with ACS-Feed andminiaturisation of the antenna structure is obtained.The modified Koch fractal shape is chosen as theradiating structure so as to excite lower frequencieswithin a smaller area. The Koch fractal shape antennaoperates in FCC approved Ultra Wideband (UWB)band but notches out the 5 GHz WLAN (4.65–6.4 GHz)frequencies to avoid interferences is reported earlier(Lui et al., 2006). Proposed modified Koch fractal shapeantenna employed for wideband operation covering3.5/5.2/5.5/5.8 GHz WLAN and WiMax band andother important wireless frequencies. Using the ACS– feed techniques, we observed the omnidirectionalradiation pattern and gain throughout the operatingband. The optimised dimensions of the tuning stuband ground for wideband operation are also presented.This antenna is simulated using the CST MicrowaveStudioTM based on the Finite Integration Time Domain(FITD) method.

2 Antenna design

2.1 Asymmetric Coplanar Strip (ACS): feeding

In this antenna design a compact and effective feedingtechnique is employed. The ACS feeding technique isused due to compactness of the antenna (Fang andWang, 1999). This feeding mechanism is analogous to thecoplanar wave guide feed expecting that the ACS feedhas single lateral ground strip compared with twin lateralstrip in the CPW feeding. These antennae are simulatedusing CST Microwave StudioTM and observed the returnloss characteristics of both ACS and CPW feedingtechnique. ACS and CPW feeding geometry are shown inFigure 1(a) and (b) having the length (LL = 10 mm) andwidth (WL = 5 mm). The dimensions of ground plane ofboth the antennae are Lg = 8.5 mm, Wg = 5 mm and thegap (g = 0.8 mm) taken for good impedance matching(Edwards and Steer, 2000).The simulated return losscharacteristics of ACS and CPW feeding are shown

Figure 1 (a) Geometry of CPW-feed antenna and(b) geometry of ACS-feed antenna

in Figure 2. Both the antennae are radiated at 6 GHzfrequency. Using the ACS feeding technique the antennagain is 2.1 dBi and for CPW feeding technique gainis 2.3 dBi. A compact ACS feeding antenna havinggood return loss and gain is presented for single bandoperation. The aim of the design using ACS feeding isminiaturise the antenna structure for having it within thespace allocated in a wireless gadget.

2.2 Design of fractal shape

Koch fractal geometry, named after the MathematicianHelge Von Koch is a well known feature that has beenapplied to miniaturise various conventional antenna.This characterised by two factors: the iteration factor(fractal factor) and the iteration order. The iterationfactor represents the construction law of fractal geometrygeneration and the iteration order depicts how manyiterations processes are carried out. Figure 3 shows theconfiguration of a koch fractal geometry curve. Figure 4shows the simulated return loss of the antenna forthe different iterations at i = 0, i = 1 and i = 2. Theresonant frequency of the slot antenna decreases withincrease the number of iterations.

Figure 2 Simulated return loss of ACS and CPW feedantenna (see online version for colours)

ACS fed koch fractal antenna for wide-band applications 11

Figure 3 The Koch curve fractal

Figure 4 Simulated return loss of diffrent iteration(see online version for colours)

2.3 Proposed ACS feed fractal shape antenna

Geometry of the proposed compact ACS fed Kochfractal shape patch antenna is described in Figure 5.The basics of the antenna structure is chosen to bea rectangular patch has dimensions of width (W =25.5 mm) and length (L = 37.5 mm). It is constructedon a substrate with relative permittivity (εr) of 4.4 andthickness (h) of 1.6 mm. The ground size of this proposedantenna is Wg = 8 mm and Lg = 13 mm is fed by 50 ΩACS feeding technique, the length and width of ACS

Figure 5 Geometry of proposed ACF-feed antenna

feed is Wf = 2.4 mm, Lf = 10 mm, gap (g = 0.2 mm).After two iterations, the basic size of the equilateraltriangle fractal shape is a = 24.3 mm.

3 Parametric study

3.1 Effect of koch

Figure 6 shows the simulated return loss of theequilateral triangle size of modified Koch fractalantenna. As per expectation, the resonant frequencyand the antenna return loss (10 dB) is increased withincreased the Koch fractal shape (a). It is observed thatthe Koch fractal geometry improves the matching ofreturn loss at lower frequency along with the bandwidthenhancement of the patch antenna. The operationalbandwidth shifted from 2.62-7.58 GHz to 2.9-8.46 GHzdecreases with size of the fractal. Further increasingthe size, it causes only a minor reduction of theoperating frequency. The following observation showsthat 10 dB return loss is good matching with a =24.3 mm.

3.2 Effect of ground plane size

Figure 7 shows the simulated return loss (10 dB)performance of the antenna, using ACS-feed techniquewith changing the ground size width (Wg). The width(Wg) has a prominent effect on the wideband matchingof the proposed fractal antenna. Although length(Lg) has almost negligible effect, therefore the length(Lg = 13 mm) is fixed for these operation of wideband.It is observed that while increasing the width ofground plane, impedance bandwidth is not increasingsubstantially. The value of Wg =10 mm is a goodmatching with return loss.

Figure 6 Simulated return loss of antenna for different Kochfractal size (see online version for colours)

12 Y.K. Choukiker and S.K. Behera

Figure 7 Simulated return loss of different ground planewidth (see online version for colours)

3.3 Effect of gap between microstrip line andground plane

Figure 8 shows the return loss of the simulated proposedfractal antenna with changing the gap (g) between lineand ground plane. It is observed that increasing the gap(g) of the Koch fractal shape antenna the simulated10 dB return loss is good matching but the resonantfrequency is shifted. Therefore the 10 dB return loss ismatching in g = 0.8 mm.

Figure 8 Simulated return loss of gap between ground planeand microstrip line (see online version for colours)

3.4 Effect of ACS feed line

Figure 9 shows the return loss of simulated proposedantenna with effect of ACS-feed line width (Wf ). It isobserved that, increasing the width of the ACS-feed linethe impedance bandwidth is increased at certain limit.Therefore the value of width is good matching withWf = 1.2 mm.

Figure 9 Simulated return loss of ACS feed microstrip line(see online version for colours)

4 Results and discussion

4.1 Return loss (S11) characteristics

Figure 10 shows the return loss characteristics of theproposed modified Koch fractal antenna for widebandapplication. It is printed on FR–4 substrate withrelative permittivity (εr) of 4.4 and the thickness ofthe patch is 1.6 mm. The simulation result is obtainedfrom CST Microwave StudioTM. The dimension of theKoch size is chosen a = 24.1 mm for the proposedgeometry. The –10 dB impedance bandwidth of theantenna is from 2.7 GHz to 7.88 GHz with resonanceat 3.24, 4.79 and 7.23 GHz. The entire bandwidthcovers the WLAN/WiMax and other important wirelessapplication bands.

Figure 10 Simulated return loss of proposed fractal shapeantenna

4.2 Radiation pattern characteristics

Radiation pattern characteristics of proposed ACS feedKoch fractal antenna is shown in Figures 11–13 at3.24, 4.79 and 7.23 GHz in the broad side direction

ACS fed koch fractal antenna for wide-band applications 13

at V = 0 and V = 90. In addition, very monopolelike radiation pattern with omnidirectional radiation isobserved. The 3 dB beamwidth at these three frequenciesare 91.8, 78.6 and 88.4.

Figure 11 Radiation pattern characteristics at 3.16 GHz(see online version for colours)

Figure 12 Radiation pattern characteristics at 4.79 GHz(see online version for colours)

4.3 Surface current distribution

The excited surface current distribution of the modifiedKoch fractal shape patch antenna is obtained from theCST Microwave StudioTM. Figures 14–16 shows thesurface current distribution at 3.24, 4.79 and 7.23 GHz.It is clear that all these three frequencies have verysimilar surface current distributions on ACS feed patch.This characteristic agrees with the radiation patternscharacteristics of all frequencies shown in Figures 11–13.Moreover, it has also been found that in this designthe surface current on the ACS-feed patch is strongand dominates the main radiation performance of theantenna. This results in a very linear polarisation patternand also agrees with the simulated radiation patternresults.

Figure 13 Radiation pattern characteristics at 7.23 GHz(see online version for colours)

Figure 14 Surface current distribution at 3.16 GHz

Figure 15 Surface current distribution at 4.79 GHz

4.4 Antenna performance (gain and totalefficiency)

When the antenna is used for wideband application ,the impedance mismatch must be taken into account fordefining its characteristics. Especially, while calculatingantenna gain and the efficiency of the antenna, ACS-feedtechnique is used to compute the gain and total efficiencyof the proposed antenna as shown in Figures 17 and 18.The maximum realised gain at the range of 3–6 dBi isobtained for the antenna and the total efficiency is ≤90%for the entire bandwidth.

14 Y.K. Choukiker and S.K. Behera

Figure 16 Surface current distribution at 7.23 GHz

Figure 17 Gain of proposed antenna

Figure 18 Total efficiency of proposed fractal shape antenna

5 Conclusion

A compact modified Koch fractal microstrip patchantenna for wideband application is designed anddiscussed. The miniaturisation is achieved by using theACS-feeding and Koch fractal geometry. The effectsof the various geometrical parameters on the Antennaperformance are studied. Simulated results show theantenna is suitable for the WLAN/WiMax and otherimportant frequencies. Due to uni-planar design , simplefeeding technique and compactness of the antennait is easy to integrate into circuit boards.

Acknowledgements

Authors would like to thank Mr. Rajeev Jyoti, GroupHead, Antenna Systems Group, Space ApplicationsCentre (SAC),ISRO Ahmedabad, India for providingsimulation facility using CST Microwave StudioTM inhis antenna design laboratory.

References

Chang, K. (Ed.) (1989) Handbook of Mmicrowave and OpticalComponents, John Wiley and Sons, New York, Vol. 1.

Chen, H.D. (2002) ‘Compact CPW-feed dual frequencymonopole antenna’, IEE Electron. Lett., Vol. 38,December, pp.1622–1624.

Chen, H.D. and Chen, H.T. (2004) ‘A CPW feeddual-frequency monopole antenna’, IEEE Trans.Antennas Propag., Vol. 52, April, pp.978–982.

Choukiker, Y.K. and Behera, S.K. (2010a) ‘Microstripline-feed modified Sierpinki fractal Monopole antennafor dual-widebands application’, IEEE InternationalConference on Communication, Control and Computing,Kanayakumari, India, pp.11–20.

Choukiker, Y.K. and Behera, S.K. (2010b) ‘CPW-feedcompact multiband Sierpinski triangle antenna’, IEEEINDICON Conference, Kolkata, India, pp.1–3.

James, J.R. and Hall, P.S. (Eds.) (1989) Handbook ofMicrostrip Antennas, Peter Peregrinus, London, UK.

Jones, H. (1990) ‘Fractals and chaos’, in Crilly, A.J.,Earnsshaw, R.A. and Jones, H.: (1993), Springer-Verleg,Newyork.

Kahrizi, M., Sarkar, T.K. and Maricevic, Z.A. (1993) ‘Analysisof a wide radiating slot in the ground plane of amicrostrip line’, IEEE Trans. Microw. Theory Tech.,Vol. 41, No. 1, pp.29–37.

Kumar, G. and Ray, K.P (2003) Broad Band MicrostipAntennas, Artech House, Inc., Norwood.

Lee, K.F., Luk, K.M., Tong, K.F., Shum, S.M., Huynh, T.and Lee, R.Q. (1997) ‘Experimental and simulation studiesof the coaxially feed U-Slot rectangular patch antenna’,Proc. Inst. Elect. Eng. Microw. Antenna Propa., Vol. 144,No. 12, pp.354–358.

Liu, W.C. and Chen, W.R. (2004) ‘CPW-feed compactmeandered patch antenna for dual-band operation’, IEEElectron. Lett., Vol. 40, No. 18, December, pp.1094–1095.

Lui W.J., Cheng C.H. and Zhu H.B (2006) ‘Compactfrequency notched ultrawide band fractal printed slotantenna’, IEEE Microwave and Wireless Compon. Lett.,Vol. 16, No. 4, pp.224–227.

Mandelbort, B.B. (1983) The Fractal Geometry of Nature,Freeman, San Francisco, CA.

Peitgen, H.O. (Eds.) (1990) Chaos and Fractals,Springer-Verleg, Newyork.

Pozar, D.M. and Schaubert, D.H. (Eds.) (1995) MicrostripAntennas, the Analysis and Design of MicrostripAntennas and Arrays, IEEE Press, New York, NY.

ACS fed koch fractal antenna for wide-band applications 15

Sappan, A. (1991) ‘A new broadband stacked two layeredmicrostrip antenna’, IEEE Trans. Microw. Theory Tech(USA), Vol. 40, p.769.

Werner D.H. and Mittra, R. (1999) Frontier ofElectromagnetic, Wiley-IEEE Press, New York.

Yang, F., Xue-Xia, Z., Xiaoning, Y. and Rahmat-Samii, Y.(2001) ‘Wide band E-shaped patch antenna for wirelesscommunication’, IEEE trans. Antennas Propag., Vol. 49,pp.1094–1100.

Fang, S.J. and Wang, B.S. (1999) ‘Analysis of asymmetriccoplanar waveguide with conductor backing’, IEEETransactions on Microwave Theory and Techniques,Vol. 47, No. 2, pp.238–240.

Edwards, T.C. and Steer, M.B. (2000) Founbation ofInterconnect and Microstrip Design, John Wiley andSons, Ltd., New York.