VERIFICATION OF MULTIBAND CHARACTERISTICS IN ITERATIVE FRACTAL ANTENNA

International Journal of Antennas (JANT) Vol.2, No.3, July 2016
DOI: 10.5121/jant.2016.2302 13
VERIFICATION OF MULTIBAND CHARACTERISTICS
IN ITERATIVE FRACTAL ANTENNA
Yogesh Babaraoji Thakare1
1
Department of E&TC Engineering, PVG’s COET, Pune Affiliated to Savitribai Phule
Pune University, Pune, India
ABSTRACT
This paper presents verification of multiband characteristics of a circularly shaped iterative fractal
antenna with increasing number of fractal iterations. The four numbers of iterations are considered for
this study. Also, the miniaturization characteristics of the fractal antenna with increasing number of
fractal iterations have been studied. The proposed 4th
iterated fractal antenna is designed on FR4
substrate (h = 1.56 mm and εr = 4.3). The antenna is coaxially fed using surface mount adapter. The
proposed circularly shaped fractal antenna is found to resonate at four centre frequencies such as 0.683
GHz, 0.97 GHz, 1.29 GHz, and 1.68 GHz. The antenna finds applications in various compact multiband
wireless communications due its smaller size , low cross polarization and multiband behaviour.
KEYWORDS
Antenna, fractal, iterative, multiband, miniaturization.
1. INTRODUCTION
Multiband antennas have wide-spread its importance in wireless communication due to
increasing demands for multichannel communication. Iterative multiband antennas are easy to
design and capable of providing hardware lock by separation among the various bands.
Advancement in wireless technologies enable various generations (1G, 2G, 3G, 4G, and 5G) of
pocket based wireless communication those need compact antennas. Fractal patch antennas are
capable of providing multiband characteristics as well as compactness. Fractal is known as
fractus in Latin language to mean “broken” or “fractured” geometry. “A fractal is a rough or
fragmented geometric shape that can be splitted into parts, each of which is (at least
approximately) a reduced-size copy of the whole” [1]. Around 1975, B. Mandelbrot has
reported existence of non-Euclidean geometries called as fractal and its use in many natural
findings. A fractal is an integral part of nature and has applications in antennas for multiband
wireless communication. The self similarity and space filling property in fractal can achieve
multiband and miniaturization characteristics in antennas. Several fractal antennas have been
reported for compact and multiband applications [1]-[16]. For faster wireless communication,
bandwidth in multiband also needs to be appropriate to exploit the available data rate in various
generations. Therefore, bandwidth enhancement becomes necessary, when bandwidth available
in multiband antenna is narrow. There are many known methods reported in the literatures [5],
[8]-[9] to enhance the antenna bandwidth those include design of the antenna with log-periodic
profile, use of a low dielectric substrate, increase of the substrate thickness, use of travelling-
wave topologies, use of efficient impedance matching and feeding techniques, use of multiple
resonators and slot antenna geometry. The field pattern of an antenna and its control is second
important parameter for effective wireless transmission and reception. The shape of the field

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pattern and its control can be easily designed using array techniques [7]. There are different
types of arrays based on excitation amplitude level and phase, spacing between the array
element and arrangement of array elements. These are uniform / non-uniform amplitude array,
uniform / non-uniform spaced array, phase scanning array, end-fire array, broadside array,
linear, circular, rectangular, random array etc based on the arrangement of the array elements.
Arrays are also capable of gain enhancement. Fractal antenna can serve as an element of an
array [7].
This work has verified the resonant behavior of the iterative fractal patch antenna reported in
[5], [8] and [11] fabricated on FR4 substrate for multiband communication using simulation and
measurement technique. Also, this work has shown the lower frequency shift in various iteration
of fractal antenna compared to their conventional counterpart.
2. DESIGN OF ANTENNA
The proposed antenna design has been reported by Y. B. Thakare etal. in [5], [8] and [11] and is
discussed below.
The design of the proposed antenna requires i. design of a conventional circular patch of 80 mm
major axis dimension with major to minor axis ratio 0.98 (Fig. 1a) and ii. loading the
conventional patch with a multi-triangular slot at 4th
iteration depth to design the fourth iterated
proposed antenna. For loading multi-triangular slot, i. first generates four equilateral triangular
slot of dimension 66 mm with its vertex at 00
, 900
1800
and 2700
in the conventional patch in
four steps as shown in Fig. 1b, 1c, 1d and 1e known as 1st
iteration fractal patch. ii. using this
fractal patch and a scale down factor of 0.7125 generate 4th
iterated proposed fractal patch as
shown in Fig.1h to design the proposed fractal antenna shown in Fig. 1i. Enough care must be
taken to electrically connect inner boundary of larger patch with the outer boundary of smaller
patch as shown in Fig. 1f. The design dimensions are given in Fig. 1i. The proposed antenna is
fabricated using on FR4 (εr = 4.3, h=1.56 mm) substrate of area 110 mm x 110 mm backed by
ground and probe fed at X= -24.85 mm and Y= 24.32 mm using 50 Ω connector as shown in
Fig. 2. This feed point is optimized for minimum reflection loss. The photo of the fabricated
antenna is shown in Fig. 3.
Figure 1. Design steps involved in the proposed antenna

15
Figure 2. Design of the probe fed antenna [5], [8], [11].
Figure 3. Photo of the fabricated antenna [5], [15], [19].
3. RESULTS AND DISCUSSIONS
3.1 Reflection loss
The probe fed conventional and the designed fractal antennas in Fig. 2 are simulated using high
frequency structured simulator based on finite element analysis method. The modelling of the
antenna is done on FR4 substrate (εr = 4.3, h=1.56 mm) as per the design dimensions as
discussed in section 2 using 3D modeller available in the simulator. The modelled antenna is
excited using wave port with 50 Ω characteristics impedance. The simulated results are obtained
by swiping the frequency between 1Hz to 3 GHz as shown in Fig. 4 and 5. The designed
antennas fabricated on FR4 are tested using Agilent vector network analyzer 0-4 GHz as shown
in Fig. 4. The simulation and measured return / reflection loss results for fourth iterated fractal
antenna are compared in Fig. 4. The simulation results of fourth iterated fractal antenna are
compared with conventional antennas of equivalent physical sizes as that of every fractal
iteration and summarized in table1. The conventional patch (base) antenna resonates at a centre
frequency of 1.04 GHz (measured) and matches closely with the simulation results as seen in
table1. The simulated and the measured results for fourth iterated fractal antenna shown in Fig.
4 and table 1 are in close agreement with small differences due to fabrication tolerance. As
shown in Fig. 5 and table 1, the proposed fourth iterated fractal antenna resonates at four
distinct frequencies measured as 0.683 GHz (first iteration); 0.97 GHz (second iteration); 1.29
GHz (third iteration) and 1.68 GHz (fourth iteration). These frequencies correspond to four

16
iterations of multi-triangular patches respectively. This is confirmed by simulating the probe fed
antenna with four, three, two and single multi-triangular patches included in the conventional
Figure 4. The reflection loss plots of probe fed proposed antenna.
Figure 5. Simulated reflection loss plot of fourth iterated proposed antenna against conventional antennas
of equivalent dimension at different iteration levels to depict miniaturization at every iteration

17
geometry. The major axis dimensions (d/2) of the multi-triangular patches considered are 40
mm, 28.5 mm, 20.85 mm and 14.85 mm respectively. Also, the probe fed conventional antennas
of same dimensions (i.e. 40 mm, 28.5 mm, 20.85 mm and 14.85 mm respectively) are simulated
and results are shown in Fig. 5 and table 1. The resulting resonating frequencies of conventional
antennas are shown by numbers 1, 2, 3 and 4 corresponding to proposed antenna resonant
frequencies numbered by 1’, 2’, 3’ and 4’ in Fig. 5. The reduction in these frequencies due to
fractal patch is about 65% (average) compared to conventional antennas of similar patch sizes as
mentioned earlier. The multiple resonating frequencies in the proposed antenna (Fig. 4);
compared to the conventional antenna resonating at 1.04 GHz (table 1) indicates multi-
functionality [9]-[16] due to fractal nature of the proposed geometry.
Table 1. Resonant frequencies of the fractal antenna and conventional antennas
Type of
antenna
Resonant
Freq.
Dimension (r)
40 mm 28.5 mm 20.85 mm 14.85 mm
Conventional
circular
patch
Simulated 1.02 GHz 1.365 GHz 1.814 GHz 2.645 GHz
Measured 1.04 GHz -- -- --
Fourth
iteration
proposed
fractal
Simulated 0.69 GHz 0.87 GHz 1.17 GHz 1.68 GHz
Measured 0.683 GHz 0.97 GHz 1.29 GHz 1.685 GHz
% reduction in freq. due
to proposed fractal
compared to conventional
patch of equivalent
dimension (simulated)
67.65 63.73 64.45 63.5
Also, the resonating frequency (1.04 GHz) of conventional (base) antenna reduces by 67.65% to
0.683 GHz with the proposed fourth iterative fractal antenna geometry. This indicates
miniaturization [4]- [5], [11] due to the proposed iterative geometry. This miniaturization is due
to the fractal slot loading [14] and space filling [1]-[4] characteristics of the antenna. The self
scaling in the antenna exhibit longer wavelength independent [2]-[4] of the classical theory is
mainly due to slot loading. Hence, the proposed fractal antenna resonates at lower frequency
than the conventional patch antenna of same size. The multi-functionality in the iterative fractal
antenna is due to self-similarity [2], [5] among the four fractal patches in the proposed antenna
geometry.
3.2 Radiation Patterns
The probe fed conventional antenna and fourth iterative fractal antenna have been simulated for
co and cross polarization at their first resonant frequencies and results are presented in Fig. 6
and Fig. 7.
These results show that cross polarization gain level has got reduced in proposed fractal antenna
compared to the conventional antenna. The probe fed conventional antenna is found to produce
the polarization difference of -3.08 dB whereas -23.66 dB in probe fed proposed fractal
antenna at theta 0 deg. as shown in Table 2. This difference reaches to -50 dB at phi = 0 and
theta = 90 deg. Thus, this fractal antenna is useful for low cross polarization.

18
Figure 6. Co and Cross polarization gain plot of probe fed fractal antenna against conventaional antenna
at their dominant resonant frequencies 0.69 GHz and 1.02 GHz respectively.
Figure 7. Co and Cross polarization gain plot of probe fed fractal antenna against conventaional antenna
at their dominant resonant frequencies 0.69 GHz and 1.02 GHz respectively.

19
Table 2. Co and Cross Polarization Gain of Probe fed Conventional against Proposed Fractal Antenna
Theta = 0
in deg.
Polarization
a-b
in dB
c-d
in dB
Conventional
Antenna
Fractal
Antenna
in dB
a b c d
Phi = 0 -3.12034 -6.20041 -9.74859 -33.40925 -3.08 -23.66
Phi = 90 -3.12034 -6.20041 -9.74859 -33.40925 -3.08 -23.66
4. CONCLUSIONS
The proposed fractal antenna can be fabricated on low cost FR4 substrate material. It is simple
in design. It exhibits multiband and miniaturization properties as compared to conventional
antenna. The multiband behavior of the antenna is due to self-similar multi-triangular slot
loading. The fourth iterated antenna exhibits four bands corresponding to four iterations that
exist in the antenna geometry. The largest size iteration (i.e. first iteration) corresponds to
lowest frequency and lowest size iteration (i.e. fourth iteration) corresponds to highest
frequency. The miniaturization in the fractal antenna is due to space–filling iterative geometry.
The fractal nature of the multi-triangular slot further enhances the compactness feature of the
antenna. The fractal antenna exhibits reduces cross polarization levels compared to conventional
patch antenna. The antenna can be designed flexibly by manipulating the size of iterations for
required frequencies. The fractal antenna is suitable for compact multiband wireless applications
and low cross polarization. The antenna can be suitable candidature for bandwidth enhancement
in future experimentation for compact broadband applications as well as radar cross section
reduction for low observability.
ACKNOWLEDGEMENTS
The authors would like to thank everyone, just everyone!
REFERENCES
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[12] K. C. Hwang (2007) “A Modified Sierpinski Fractal Antenna for Multiband Application",
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Authors
YOGESH BABARAOJI THAKARE
Short Biography
Yogesh B. Thakare (mother-Sushilabai) is passed BE E&TC in the year 1998 with
first class from VYWS College of Engg., Badnera, Amravati University
(Maharashtra -India), ME E&TC (Microwave) in the year 2006 from Govt. College
of Engg., Pune, Pune University (Maharashtra-India) in first class and Ph.D.
(Electronics) from Shivaji University, Kolhapur (Maharashtra- India) in 2015. He
has about 15 years teaching and 02 years industrial experience. He is currently
working with PVG’s College of Engineering and Technology, Parvati, Pune
(Maharashtra-India) as ASSISTANT PROFESSOR in the department of electronics and
telecommunication Engg. He taught major subject like wave theory and ante nna, microwave engineering,
semiconductor devices and technology, analogue and digital communication engineering. He has 04
international and 01 national journal and 05 international and 04 national conference publications. His
current research interest is in wave propagation techniques, microstrip antenna engineering,
communication engineering and semiconductor electronics.

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