JOURNAL OF TELECOMMUNICATIONS, VOLUME 23, ISSUE 2, JANUARY 2014

1

Sierpinski Triangular Antenna on a Mushroom-like EBG Metamaterial Ground

Plane S. Sahandabadi, F.H. Kashani and M. Fallah

Abstract— In this paper, a triangular microstrip patch antenna with fractal geometry and microstrip feedline is designed,

simulated and fabricated on two substrates: traditional substrate and Electromagnetic Band-Gap (EBG) ground plane. The

simulation of these antennas is conducted using Ansoft HFSS software. Corresponding results for return loss and radiation

pattern of the antennas is demonstrated for simulation and fabrication. The triangular fractal antenna with traditional ground

plane (PEC ground plane) is simulated and the results have been compared with the antenna placed on EBG ground plane.

Antenna is designed to operate in X band and at 8.85 GHz of resonance frequency. The basic designed model has the

dimension of 11.8984 on a substrate with 1.575mm thickness and 2.2 of permittivity.

Index Terms— Antenna Size Reduction, Fractal Antenna, EBG Ground Plane, Microstrip Antenna, Sierpinski Fractal, Triangular

Patch, Resonant Frequency.

—————————— ——————————

1 INTRODUCTION

EVERAL methods have been used for reducing an-tenna size, such as adding dielectric loading[1] and meandering[2]. Fractalization can be used to reduce

the physical area of antenna. The word "fractal" was first proposed by Mandelbrot to describe some complex fig-ures which have selfsimilarity in their geometrical struc-ture [3]. Using fractal geometry has received attention in various fields of engineering. One of these areas is anten-na design. Some fractal structures have been able to re-duce the size of antenna significantly [4]. It implies that the electrical size of antenna is larger than its physical size. Some of these structures provide access to multiple frequency bands. The method used in this work is fractalizing in the form of Sierpinski triangles on a triangular antenna. Then we try to obtain more decrease in resonant frequency using EBG structure. Mushroom-like configuration has an effective bandgap for surface wave propagation. It can be used for improv-ing the radiation pattern of antenna [5]. In the previously published works, the performance of a dipole antenna on a ground plane has been improved utilizing EBG surface [6]. In this work a triangular patch is designed and fabricated to work in X band. Then the antenna is designed, simu-lated and fabricated in the form of triangle and Sierpinski triangle on traditional ground plane and EBG ground plane, which resulted in resonace frequency decrease. The

measured results are compared to simulation results and they were well-matched. The comparison shows reducing in the resonant frequency. The application of this antenna is in telemedicine mobile devices and military applica-tions in X band.

2 DESIGN

To obtain the dimension of antenna, we act in the follow-ing way. For the m, n mode and the given resonant fre-quency equaling to 10GHz, the side length of equilateral triangle is obtained from the following equations [7]:

22

3

2nmnm

a

cf

r

r

(1)

r is the relative permittivity of substrate. With consider-ing the dominant mode of TM10 and the RT Duroid 5880 substrate with 1.575mm of height and 2.2 of permittivity, the side length of 11.8984mm and effective side length of 13.48mm is obtained. The size of rectangular patches in the artificial ground is obtained as follows. Having resonant frequency of struc-

ture we have: LC

10 and L=μh which h is the height of

substrate. Then we calculate the edge capacitance from the following equation:

)(cosh)1( 10

g

gWWC r

(2)

Which W is the patch width; g is the gap between the patches and r is the relative permittivity of substrate [8]. Using a program in MATLAB, the dimension can be cal-culated from the previous expression.

————————————————

S. Sahandabadi is with the Electrical Engineering Department of Islamic Azad University, South Tehran Branch, Tehran, Iran.

M.Fallah is with the Electrical Engineering Department of Malek Ashtar University of Technology, Tehran, Iran.

F.H.Kashani is with the Electrical Engineering Department of Iran Uni-versity of Science and Technology, Tehran, Iran.

S

2

3 COMPARISON OF SIMULATION AND FABRICATION

RESULTS

The basic geometry used in microstrip patch is an equila-teral triangle shown in fig.1. The simulated return loss of antenna is shown in fig.2. As seen, the first resonant frequency of this antenna oc-curring in 9.43GHz is compatible with the results of de-sign. Fig.3 shows the radiation pattern for triangular an-tenna with traditional PEC ground plane.

Fig. 1. Simple triangular patch antenna on traditional PEC ground

plane

Fig. 2. Return loss of triangular patch antenna on traditional PEC

ground plane Simulated by HFSS

Fig. 3. Radiation pattern of triangular patch antenna on traditional

PEC ground plane simulated by HFSS

The fabricated antenna on the traditional PEC ground plane is shown in fig.4. The return loss of this antenna shown in fig.5 is in agreement with simulation results. The radiation pattern of the antenna is presented in fig.6.

Fig. 4. Fabricated triangular antenna on traditional PEC ground

plane

Fig. 5. Return loss of triangular patch fabricated on traditional PEC

ground plane

Fig. 6. Radiation pattern of triangular antenna fabricated on tradi-

tional PEC ground plane at the frequency of 8.85GHz

The structure of triangular antenna on EBG substrate is shown in fig.7. The high impedance surface (HIS) has provided a kind of artificial ground plane for our low profile antenna so that the image currents are in same phase with antenna currents and the radiating elements radiate more effectively. The return loss of triangular patch antenna on EBG ground plane is shown in fig.8. Comparing to triangular antenna with traditional PEC ground plane, 26% decrease is seen in resonant frequency. The radiation pattern of this configuration is shown in fig.9.

Fig. 7. Triangular patch antenna on EBG ground plane

3

Fig. 8. Return loss of triangular patch antenna on EBG ground plane

simulated by HFSS.

Fig. 9. Radiation pattern of triangular patch antenna on EBG ground

plane simulated by HFSS.

The fabricated triangular antenna on artificial ground plane is presented in fig.10. The first resonant frequency of this configuration is 6.55GHz which is seen in fig.11. This structure shows 2.3GHz or 26% decrease in resonant frequency. The radiation pattern of triangular antenna on artificial ground plane is shown in fig.12 and fig.13.

Fig. 10. Triangular antenna fabricated on EBG ground plane (the right

figure shows the antenna and the left figure depicts the artificial ground plane)

Fig. 11. Return loss of triangular antenna fabricated on EBG ground

plane.

Fig. 12. Radiation pattern of triangular antenna fabricated on EBG

ground plane at the frequency of 6.38GHz.

Then the first iteration of Sierpinski fractal is simulated. Using fractals, the electrical length of antenna can be in-creased. It is because of increase in the path length where the current travels along the antenna surface. Having less physical length or area, the current travels more path length, resonant frequency is substantially reduced. Each iteration of the Sierpinski fractal reduces some percentage of physical area of antenna. The first iteration of Sierpins-ki patch antenna on the traditional PEC ground plane is shown in fig.14. We add small triangles at the midpoints of the original triangle or at the vertices of new triangle to make the simulation and fabrication process possibile. The first resonant frequency of antenna is at the 8.375GHz which shows 1GHz or 11% decrease in resonant frequen-cy compared to simple triangular patch and is shown in fig.15.

Fig. 13. Radiation pattern of triangular antenna fabricated on EBG

ground plane at the frequency of 6.55GHz

Fig. 14. The first iteration of Sierpinski fractal antenna on traditional

PEC ground plane

4

Fig. 15. Return loss of first iteration of Sierpinski fractal antenna on

traditional PEC ground plane simulated by HFSS

In the next step, the first iteration of sierpinski antenna on traditional PEC ground plane is fabricated. This configu-ration is shown in fig.16. The resonant frequency of this step is 8.325GHz which shows 525MHz or 6% decrease compared to the triangular antenna on traditional PEC ground plane (fig.17).

Fig. 16. The first iteration of Sierpinski fractal antenna fabricated on

traditional PEC ground plane

Fig. 17. Return loss of first iteration of Sierpinski fractal antenna

fabricated on traditional PEC ground plane

Now we investigate the results of simulation of the first iteration of Sierpinski triangle on EBG ground plane. In order to compare the results well, we have tried to keep all parameters constant, as far as possible, compared to other cases. The first iteration of Sierpinski antenna on EBG ground plane is shown in fig.18. The return loss of this antenna is presented in fig.19.

Fig. 18. The first iteration of Sierpinski fractal antenna fabricated on

EBG ground plane

Fig. 19. Return loss of first iteration of Sierpinski fractal antenna on

EBG substrate simulated by HFSS. Then we fabricated the first iteration of Sierpinski anten-na on EBG ground plane. It is shown in fig.20. The first resonant frequency of this antenna is 6.375GHz which omparing to the first iteration with traditional PEC ground plane shows 1.95GHz or 23% decrease. The return loss of this antenna is shown in fig.21.

Fig. 20. The first iteration of Sierpinski fractal antenna fabricated on

EBG ground plane (the EBG layer is located under the antenna).

Fig. 21. Return loss of first iteration of Sierpinski fractal antenna

fabricated on EBG ground plane

7 CONCLUSION

In this paper, the resonant frequency of triangular anten-na on EBG ground plane shows 26% decrease compared to triangular antenna on traditional PEC ground plane. Fractalization, also increase the current path and there-fore decrease the resonant frequency and physical size of antenna.

According to equation (1), the resonant frequency is reversely related to side length of antenna. Accordingly, we can justify the deacrease in antenna size in the follow-ing way. We can achieve the desired resonant frequency with smaller structure. The results of simulation and fa-brication are in good agreement. In table 1, the decreasing procedure is shown both in simulation and fabrication process.

5

TABLE 1 RESONANCE FREQUENCIES OF DIFFERENT CONFIGURATIONS

OF ANTENNA DESIGN

simulation/

fabrication substrate

Resonant

frequency

Iteration

of Sierpinski

simulation simple 9.43 0

simulation simple 8.375 1

simulation EBG 6.99 0

simulation EBG 6.65 1

fabrication simple 8.85 0

fabrication simple 8.325 1

fabrication EBG 6.55 0

fabrication EBG 6.375 1

We can use this antenna where the size of antenna is

an important factor. This antenna can be used in military applications, medical applications and sensors.

REFERENCES

[1] Young, M.B, “Reducing the size of helical antennas by means of dielec-

tric loading,” Pulsed Power Conference, IEEE, 2011, p. 575-579.

[2] Li Deng, Shu-Fang Li, Ka-Leung Lau, and Quan Xue, “Vertical

Meandering Approach for Antenna Size Reduction,” Interna-

tional Journal of Antennas and Propagation, vol. 2012.

[3] B.B.Mandelbrot, "The Fractal Geometry of Nature",

W.H.Freeman and Company, New York, 1982

[4] Mirzapour, B. Hassani, H.R. ,"Size reduction and bandwidth

enhancement of snowflake fractal antenna", IET Microwaves,

Antennas & Propagation, Volume 2, Issue2, 2008, p.180-187

[5] F. Yang, Yahya Rahmat-Samii, “Reflection Phase Characteriza-

tions of the EBG Ground Plane for Low Profile Wire Antenna

Applications”, IEEE Transactions on Antennas and Propaga-

tion, Vol. 51, No. 10, October 2003.

[6] F. Yang, V. Demir, D. A. Elsherbeni, and A. Z. Elsherbeni, "En-

hancement of Printed Dipole Antennas Characteristics Using

Semi-EBG Ground Plane", Journal of Electromagnetic Waves

and Applications, Vol. 20, No. 8, 2006, pp. 993-1006.

[7] David A. Sanchez-Hernandez, “Multiband Integrated Antennas

for 4G Terminals,” Artech House, INC. 2008.

[8] F. Yang, Y. Rahmat-Samii, “Electromagnetic Bandgap Struc-

tures in Antenna Engineering,” Cambridge University Press

2009.

S. Sahandabadi received her B.S. and M.S. degrees both in elec-trical engineering from Tabriz University and Islamic Azad University Tehran South Tehran Branch, respectively.

F.H. Kashani received his B.S. degree in Electrical Engineering from University of Tehran, M.S. degree in Electrical Engineering from UCLA and Ph.D. degree in Electrical Engineering from University of California Los Angeles, in 1962, 1968 and 1970, respectively. He is full Prof. of Electrical Engineering of Iran University of Science and

Technology. His Expertise is about Antenna Design, Microwave and Millimeter Wave Community, Metamaterials and EBG structures. He has more than twenty Research and Industrial Projects as "Design and Implementation of a Conical Wraparound Antenna".

M. Fallah received his B.S. degree in Electrical Engineering from Isfahan University of Technology and M.Sc. and Ph.D. degrees from Iran University of Science and Technology. His current research interests include microstrip antennas, passive and active microwave devices, metamaterials and EBG structures, and electromagnetic theory.