A Novel Swastik Shaped Spidron Fractal Array
Antenna for S-Band Applications
Swetha Amit 1, Chinmoy Kumar P R 2, Nayana Arvind Laxmeshwar3, Saurabh R Badenkal4
1
Assistant Professor, Dept. of Telecommunication Engg. M S Ramaiah Institiue of Technology, Bangalore-54
2, 3, 4
B.E Students, Telecommunication Engg. M S Ramaiah Institiue of Technology, Bangalore-54
[email protected]
[email protected]
[email protected]
[email protected]
Abstract: Fractal geometries have shown to be attractive
for antenna designers because of the unique features they
offer. In this paper, a dual-resonant frequencies Swastik
shaped Spidron arm fractal slot antenna array of four
elements with two feed lines and a single port is developed
for Satellite communication/ IEEE 802.11b and 802.11g /
WiMAX. The fractal antenna is fed by two micro strip
lines at end of substrate for resonance at 2GHz and
3.8GHz. The antenna structure on the substrate has
dimensions of 55mm*55mm*1mm. A conducting reflector
is placed at a distance k=17mm under the substrate to
reduce back radiation from the fractal antenna, thereby
enhancing the antenna gain. The positioning of the micro
strip feeder is done in such a way so as to reduce the
coupling losses. The single element Spidron antenna is
structured for 10 iterations. Results of 10 iteration
Spidron arm fractal slot antenna for each array element
indicate 10db reflection coefficient at all the above said
resonant frequencies.
Index terms: Swastik-shape, Spidron arm Fractal, KochLike antenna, Slot antenna array, Dual-band, micro strip
feed, coupling loss.
I.INTRODUCTION
In today world of wireless communications, there has been an
increasing need for more compact and portable
communications systems. Fractal geometry antennas are being
studied in order to answer those requirements. Fractal antenna
theory uses a modern (fractal) geometry that is a natural
extension of Euclidian geometry. The project undertaken was
to construct antennas using fractal patterns in order to obtain
desired performance properties such as compact size and
multi-band behavior. One of the prevailing trends in modern
wireless mobile devices is a continuing decrease in physical
size. In addition, as integration of multiple wireless
technologies becomes possible, the wireless device will
operate at multiple frequency bands. A reduction in physical
size and multi-band capability are thus important design
requirements for antennas in future wireless devices. The use
of fractal patterns in antenna design provides a simple and
efficient method for obtaining the desired compactness and
multi-band properties. Fractals can be constructed using
iterations; this procedure is normally called Iterated Function
systems (IFS). Fractals are made up from the sum of copies
from itself; each copy will be smaller copy from the previous
iterations. The fractal antenna not only has a large effective
length, but the contours of its shape can generate a
capacitance or inductance that can help to match the antenna
to the circuit.
Microstrip antennas were born of microstrip circuit
technology and inherited many characteristics, such as low
radiating efficiency and narrow bandwidth that are
undesirable for a radiator [6] .Owing to the low profile, light
weight, and the ease with which they can be integrated with
active devices [5], microstrip antennas have become widely
used over the past few decades. For dual-band operation, dualport micro strip feeding lines are used [3]-[4]. The length of
the microstrip lines is selected, so that the antenna resonates at
a particular operating frequency (/3 ≤ fs1 ≤ /2). The length
of the stripline needs to be tuned to account for the fringing
fields at the edges of the patch. Finally, the width of the patch
is used to adjust the input impedance of the antenna. The
feedlines are arranged in a manner to reduce coupling losses.
In the paper, we propose a dual-resonant frequency antenna
that utilizes an aperture-shaped Spidron fractal slot on a single
substrate. Array of 4 elements is structured to form a shape of
Swastik. The proposed antenna has only one radiating port
which is fed by two conventional micro strip feeding lines.
Positioning of the striplines was done to verify the
performance of the antenna. Details on the proposed antenna
with 10 iterations of Spidron slot fractal antenna and their
performance evaluation is discussed in following sections.
With array of 4 elements, dual resonant frequency in S-band
are obtained which is used for applications in Satellite
communication, IEEE 802.11b and 802.11g / WiMAX.
The bandwidth is increased as compared to 7 iterations which
has been discussed [7]. A conducting reflector at the bottom
of the fractal antenna is used to enhance the gain. The
reflector is placed at a distance of /4 which is 17mm.
II.SINGLE SPIDRON FRACTAL SLOT ANTENNA
A. Single Antenna Configuration
Parameter
Value
Parameter
Value
α
35.5
sw1
1.8 mm
h
36.5mm
sh1
20 mm
t
1 mm
sd1
33.1 mm
mw
55 mm
sw2
1.8 mm
mh
55 mm
sh2
15.5 mm
k
17 mm
sd2
19.6 mm
Table 1: Dimensions for the proposed antenna.
III.ANALYSIS OF ANTENNA ELEMENT
The antenna was simulated using an ANSYS high-frequency
structure simulation (HFSS) based on a three-dimensional
finite element method (FEM). [9]
Figure 1: Geometry of the antenna with front view and side
view.
The array configuration is shown below. It is formed by
combining the base of the four single spidron structures to
form a shape of Swastik.
Figure 1 show the configuration and design parameters for the
Swastik shaped Spidron Fractal array antenna proposed in this
paper. A Spidron fractal is a plane figure that is iteratively
constructed from a series of progressively smaller, contiguous
right triangles using a common angular factor (α) as shown in
figure 2. [1]
Figure 3: Proposed Spidron arm Fractal array antenna
Iteration 10
Figure 2: Iterations of Spidron Fractal Slot Antenna.
Let the dimensions of the 1st triangle be ‘a’ mm x ‘b’ mm x ‘c’
mm as shown in the Figure 2.Then for the next iteration
triangle the scaling factor ‘S’ is given by
S (scaling factor) =
, for 0
45
Therefore the 3 sides of the new triangle are got by scaling
down all the 3 sides by S.
Let a1, b1 and c1 be the dimensions of the new triangle such
that a1=S*a, b1=S*b, c1=S*c, then the perpendicular a1 is
placed on hypotenuse of the 1st triangle to get the 2nd figure.
This is termed as 2nd iteration. The same process is continued
up to 10 iterations.
The Spidron fractal-shaped slot is etched on the ground plane
(the upper side) of a FR-4 epoxy substrate with a permittivity
constant of  =4.4 and a thickness of t=1 mm. In this antenna
design, the sequence for the Spidron fractal generation is
repeated ten times in the direction of increasingly smaller
triangles. The antenna is built for a single element and then a
array configuration is framed. Two 50Ω microstrip feeding
lines are located on the bottom side of the substrate to excite
the Spidron fractal array. The overall dimension of the
proposed antenna is 55mm*55mm*1mm. In the proposed
antenna design, a conducting reflector is adopted to block
back radiation from the Spidron arm fractal slot. The distance
of the conducting reflector is placed at a distance of 17mm,
thus reducing back radiation and enhancing the gain. The
reflector distance is chosen to be 17mm which is λ/4.[2]
IV.SIMULATED RESULTS
3.8GHz, the antenna is resonating at 50 impedance with its
inductive and capacitive components going to zero.
The proposed Swastik shaped Spidron arm Fractal slot array
antenna is designed for 10 iterations. By constructing 10
iterations the S-parameters are improvised that with its lower
iterations. The substrate with the slot and feeding lines is
attached to reflector using four foam supports which have a
relative permittivity of 1.06. With array configuration of 4
elements, the antenna is tuned to resonate for S-band
frequency.
The simulation results show the VSWR plot, S parameters,
Smith chart and radiation pattern. Depending on impedance
matching, the standing wave ration can be evaluated. From the
simulation results of the S11 parameters, their values are -33.25
dB and -23.32 dB for 2GHz and 3.8GHz respectively as
shown in figure 4. Its corresponding values of VSWR are 1.04 and 1.14 for dual frequencies of 2GHz and 3.8GHz
respectively as shown in figure 5. Thus the antenna is
resonating at the above said frequencies to have applications
on Satellite communication, IEEE 802.11b and 802.11g /
WiMAX.
Figure 6: Smith chart
Figure 7a and 7b shows the 3D radiation pattern for the
proposed antenna.
Figure 4: S11 Parameters.
Figure 7a: Radiation pattern.
Figure 5: VSWR.
The input impedance is plotted using a Smith Chart. It would
determine any of the antenna’s resonance frequencies. The
impedance of the antenna is adjusted through the design
process to be matched with the feed line and have less
reflection to the source. The Smith chart is as shown in
figure6 which tells that at the resonant frequencies 2GHz and
Figure 7b: Radiation pattern.
V.CONCLUSION
A dual resonant frequency Swastik shaped Spidron fractal
slotted array antenna is proposed, designed, and simulated in
this study. A novel Spidron fractal slot was utilized with
VSWR values very close to 1 and thus providing high
impedance matching and dual band resonance and a favorable
coupling level is obtained. The resonating frequency bands at
2GHz and 3.8GHz serves applications for Satellite
communication, IEEE 802.11b and 802.11g / WiMAX.
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