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A Compact Monopole Fractal Antenna for TV White
Space Energy Harvesting Applications
A. Goyal, A. Alphones
School of Electrical & Electronic Engineering
Nanyang Technological University, Singapore
E-mail: ealphones@ntu.edu.sg
M. F. Karim, L. C. Ong, Nasimuddin
Institute for Infocomm Research, Singapore
E-mail: kfaeyz@i2r.a-star.edu.sg
Abstract—In this paper, a compact monopole fractal antenna for
the TV white space frequency band is designed and fabricated for
energy harvesting applications. The monopole is designed by the
combination of modified Giuseppe Peano fractal geometry and
impedance steps and fabricated on a 1.6mm thick FR-4 substrate.
The feeding circuit is designed to be a microstrip line with a semi-
circular ground plane. The antenna resonates at 600MHz and
shows omni-directional radiation patterns with a measured gain
of 1.71dBi. A size reduction of 52% is achieved as compared to
the conventional planar monopole antenna.
I. INTRODUCTION
Mandelbrot first introduced the fractal geometry in 1975
[1], in which each sub-section has the characteristics of the
whole structure in a smaller scale. This leads to the basic
property of self similarity. Fractal geometries have been
applied to antennas where it tends to reduce the physical size
and generates multiband response. Fractal structures have
repetitive geometry and can generate long paths in a limited
volume. Popular fractal geometries that have been applied on
dipole and ring antennas are the Koch, Minkowski, Hilbert, and
Giuseppe Peano fractals [2-3].
In this paper, a compact fractal monopole antenna for the
energy harvesting applications at TV white space band is
presented. The antenna is realized by the combination of
Giuseppe Peano fractal which has been modified for
maximizing miniaturization and the introduction of impedance
steps [4]. The presented antenna has omni-directional radiation
pattern and the size has been reduced.
II. DESIGN OF GIUSEPPO PEANO MONOPOLE
FRACTAL ANTENNA
The Giuseppe Peano fractal initiator and generator are shown
in Fig. 1. In order to reduce the size of the antenna or to
decrease the resonant frequency of the planar monopole patch,
the 1st iteration of Peano fractal is applied on the boundaries of
the radiating patch [4]. The length of the side of the patch is
divided into five longer portions and three shorter portions.
Both the portions are derived from the ratios of the side length.
The longer portion ratio is depicted as F (= F_L/L) and the
shorter portion ratio is depicted as E (= F_W/L), where L is the
length of the square patch as shown in Fig. 2.
Figure 1: Initiator, generator and Giuseppe Peano fractal geometry
For omnidirectional patterns, partial circular ground plane
is used which flushed the feed line [4]. The radius of the
circular ground has been optimized to 53.67mm. The circular
ground in addition helps in impedance matching and further
increases the bandwidth of the antenna. Fig. 3 shows the
simulated return loss response of the antenna. The resonant
frequency is centered at 700MHz.
(a) (b)
Figure 2: Giuseppe Peano fractal-shaped monopole antenna
(a) top side, and (b) back side
Figure 3: Simulation S11 of Giuseppe Peano fractal antenna
2437978-1-4799-7815-1/15/$31.00 ©2015 IEEE AP-S 2015
To further decrease the size or the resonating frequency of
the fractal antenna, some slits were introduced in the patch. The
modified Peano fractal is as shown in Fig. 4. The width and
length of the slits are of the same dimensions as the interdigital
slot of the Peano fractal. The dimensions of the teeth and slits
were optimized using CST Microwave Studio and are set to be
26.35mm by 2.55mm. In order to increase the bandwidth
requirements and improve the matching, impedance steps are
introduced. The simulation for the modified Giuseppe Peano
fractal antenna is shown in Fig. 5 which shows that the
resonant frequency has been further reduced to 600MHz.
Figure 4: Structure of the modified fractal antenna
Figure 5: Simulation S11 of the modified fractal antenna
III. MEASUREMENT RESULTS AND DISCUSSIONS
The modified Giuseppe Peano fractal antenna was
fabricated on a FR-4 substrate with thickness of 1.6mm and
dielectric constant of 4.4. This is shown in Fig. 6.
Figure 6: Fabricated fractal antenna
The measured S11 is plotted as shown in Fig. 7. Two major
resonances at 600MHz and 900MHz can be seen clearly in the
S11 plot in both the simulated and measured results. The
normalized measured and simulated radiation patterns are
compared in both planes at the 600MHz resonance frequency.
Omni-directional patterns are obtained as depicted in Fig. 8.
The measured gain is 1.71dBi, in comparison to the simulated
gain of 1.88dBi.
Figure 7: Measured S11 of the modified fractal antenna
Figure 8: Normalized measured and simulated radiation patterns
IV. CONCLUSION
A miniaturized planar fractal monopole antenna has been
demonstrated by applying the modified Giuseppe Peano
fractal and impedance steps. The designed antenna has an
omni-directional radiation pattern with a measured gain of
1.71dBi. A size reduction of 52% has been achieved compared
to the conventional planar monopole antenna. The proposed
fractal-based monopole is useful for low frequency planar
designs.
REFERENCES
[1] D. H. Werner and R. Mittra, “Frontiers in Electromagnetics,”
IEEE Press, pp. 48-81, 2000.
[2] J. P. Gianvittori and Y. Rahmat-Samii, “Fractal Antenna: A
Novel Antenna Miniaturization Technique and Applications,”
IEEE Ant. Propag. Mag., 44(1), 2002.
[3] D. H. Werner and S. Ganguly, “An Overview of Fractal Antenna
Engineering Research,” IEEE Ant. Propag. Mag., 45(1), 2003.
[4] H. Oraizi and S. Hedayati, "Miniaturization of Microstrip
Antennas by the Novel Application of the Giuseppe Peano
Fractal Geometries," IEEE Trans. Ant. Propag., 60(8), pp. 3559-
3567, 2012.
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