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Characterization of a Self-complementary Sierpinski GasketMicrostrip Antenna

B. N. Biswas1, Rowdra Ghatak2, Rabindra K. Mishra3, and Dipak R. Poddar4

1Academy of Technology, P.O Aedconagar, Adisaptagram, Hoogly, West Bengal-712121, India2Physics Department, Burdwan University, Burdwan-713104, West Bengal, India

3ALCEAST, Sambalpur University, Burla, Sambalpur-768018, Orissa, India4Electronics and Telecommunication Engineering Department, Jadavpur University, Kolkata-32, India

Abstract— Fractal antennae are recent topic of research interest. This work reports a self-complementary Sierpinski Gasket fractal microstrip patch antenna. The first iteration is namedCSMASLI1, which stands for Complementary Sierpinski Microstrip Antenna Same Layer Iter-ation 1 and similarly the second iteration is named as CSMASLI2. The antennas are analyzedfor two iterations using commercially available electromagnetic simulation software IE3DTM andCST Microwave StudioTM. The antenna radiates prominently at all resonant frequencies. Theimpedance bandwidth increases at higher harmonics. The radiation pattern is consistent for thedifferent resonant frequencies and for different iterations. However some undulations are ob-served at higher resonance. Thus this new design can have usage in vehicle-mounted antenna formultiband wireless systems. A prototype was experimented which matches simulated results.

DOI: 10.2529/PIERS060901153618

1. INTRODUCTION

Fractal antenna provides a paradigm shift to the conventional planner antenna technology. Whilethe later is in commercial practice, the former is in the process of descending to this practice from thenovelty of academics. In general, they exhibit multi resonant frequencies like a log periodic antenna.They can be thought of as a special case of log periodic antenna which folds inward. Sierpinskifractal monopole antenna has been reported in [1]. The self-complementary Sierpinski gasketmonopole was reported in [2]. Empirical formulae of resonant frequency and input impedancesfor some geometry are available in literature [1, 3]. Some other fractal structures reported in [4]include self-complementary versions of the Koch tie dipole and the Gosper Island dipole. The duallayer complementary Sierpinski microstrip antenna has been reported by the present authors in [5].

Here we have tried to implement the benefits of the complementary structure on the same planeand came up with the Sierpinski quasi-complementary microstrip pre-fractal patch antenna. Thefeed point was judiciously chosen to provide good match at the resonant frequencies. However thebehavior replicates with higher iteration, as they are basically self-similar structures.

2. DESIGN

The antenna structure is generated by an initial right-angled triangle with base s and height has shown in Figure 1. The right half plane is the complementary of the left half plane. Thefundamental triangle is tessellated to form the entire geometry.

The parameters h and s becomes half with every iteration. Thus the number of replicationsincreases to form the geometry. For example the first iteration is made of 8 such right-angledtriangles. This gives a surface area for first iteration as a1 = 4hs. For the second iteration the newheight and base is half of h and s respectively. But now we require 30 such triangles to generate

the structure. So area of the second iteration geometry is a2 =18hs × 30 = 3.75hs and for third

iteration it is a3 = 3.5hs. Thus in general the area for various iteration is given as

a ∼= 41.076I−1

hs

}I = 1, 2, 3 . . . (1)

In the Equation 1, I denotes the iteration. For increasing iteration the surface area decreases butthe number of corners and edges increases and the current is allowed to meander longer distances.This however increases the electrical length. The geometry is constructed on a CuCLAD substrate

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of εr = 2.54 and tan δ = 0.0009. The thickness of the substrate is 1.59mm. The starting value ofs and h is 7.5mm and 12.9904 mm respectively. The feed is via a SMA coaxial probe arrangementas shown in Figure 1 with a black dot.

s

h

Figure 1: The starting right-angled triangle of base s and height h. The steps followed in tessellating thefundamental triangle to form the entire geometry of first iteration are also shown.

3. RETURN LOSS CHARACTERISTICS

The antenna was simulated in IE3D and CST Microwave Studio till second iteration. The same wereexperimented to obtain the S11 characteristics using a HP8722C vector network analyzer as shownin the Figure 2. In CST Microwave Studio we have modeled a coaxial feed arrangement to resemble

Figure 2: Setup of HP 8722C VNA for measuring return loss measurement of CSMASLI2.

the actual fabricated structure. The simulated and experimental return loss is compared for seconditeration in Figure 3. This structure considerably enhances the resonance peaks at the lowerfrequencies for second iteration, in the band of interest, compared to a simple Sierpinski antenna.From experimental results we see that for the second iteration impedance bandwidth increases from2% at the first resonance to 4% at the third resonance. The simulated and experimental resultsare in good agreement.

-35

-30

-25

-20

-15

-10

-5

0

1 2 3 4 5 6 7 8 9 10 11 12

IE3D

CST MWS

EXPT

Figure 3: Return loss of self-complementary Sierpinski microstrip antenna of second iteration.

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4. RADIATION CHARACTERISTICS

The radiation patterns of CSMASLI1 at 4.025 GHz and CSMASLI2 at 3.987 GHz are presented inFigure 4(a) and (b). The last resonance at 10.39 GHz of CSMASLI2 is shown in Figure 4(c). Theradiation pattern is consistent for the different resonant frequencies and for different iterations asseen in Figure 4. An interesting phenomenon is observed that with increasing resonant frequenciesthe patterns show some undulations. This can be physically explained by taking in to account thediffraction effect at higher frequencies.

(c)

(b)

(a)

Figure 4: E-Phi and E-Total radiation pattern for (a) first frequency f = 4.025Ghz of first iteration (b)first resonance f = 3.987GHz of second resonance (c) third resonance of second iteration f = 10.39GHz.

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5. CONCLUSION

Experimental and simulated results of CSMASLI1 and 2 have been presented. A general approachto the design of the antenna has been reported in this paper. The resonant frequencies are prominentat all resonance. This property is however not seen in the Sierpinski geometry microstrip patchantenna as well as monopoles where the lower resonances are less emphatic. The present structure,which is a variation from conventional fractal geometry, gets focused as possible candidate for truemultiband operation. The physical area of the antenna decreases with increasing iteration but thenumber of resonance increases. The radiation characteristics show uniformity for both the iterationsand among different resonance in a given iteration. The overall characteristics support its inclusionin the family of fractal antennas and its variations.

REFERENCES

1. Baliarda, C. P., J. Romeu, R. Pous, and A. Cardama, “On the behavior of the Sierpinskimultiband fractal antenna,” IEEE Transactions on Antennas and Propagation, Vol. 46, No. 4,517–524, April 1998.

2. Siah, E. S., B. L. Ooi, P. S. Kooi, and X. D Xhou, “Experimental investigation of several novelfractal antennas-variants of the sierpinski gasket and introducing fractal fssscreens,” IEEECNF, 170–173, 1999.

3. Musliake, Y., “Self-complementary antennas,” IEEE Transactions on Antennas and Propaga-tion, Vol. 34, No. 6, 23–29, Dec. 1992.

4. Gonzalez-Arbesu, J. M. Rius, and J. M. Romeu, “Some pre-fractal self-complementary anten-nas,” IEEE APS Int. Symposium, Vol. 4, 3449–3452, 20–25 June 2004.

5. Ghatak, R., R. K. Mishra, D. R. Poddar, and A. Patnaik, “Multilayered complementary quasi-fractal sierpinski patch antenna for wireless terminals,” URSI XXVIII GA Poster PresentationsProgramme, 95, 2005.