Dual band Minkowski fractal slot antenna for WLAN applications
Venkateshwar reddy V
N.V.S.N Sarma
Research scholar, Department of
Electronics and Communication Engineering
National Institute Of Technology, Warangal
Warangal, India
vvreddy2005@gmail.com
Professor, Department of
Electronics and Communication Engineering
National Institute Of Technology, Warangal
Warangal, India
Abstract— A novel circularly polarized fractal slot
microstrip antenna is presented. Perturbation to the
structure for circular polarization is introduced by
replacing the sides of the square patch with
asymmetrical fractal curves. A rotated fractal slot by 450
is embedded in the middle of the patch for dual band CP
radiation. The simulated 10-dB return loss bandwidths
are 10%, 5.2% at 2.4 GHz and 5.8 GHz respectively.
The proposed antenna covers the WLAN bands at 2.4
GHz and 5.8 GHz. The gain of the antenna over the both
operating bandwidths is more than 4-dBi.
sarma@nitw.ac.in
curves. The proposed fractal antenna can be obtained by
replacing the sides of the square patch with Minkowski
fractal curves. A fractal slot which is a scaled version of the
original Minkowski patch rotated by 450 is embedded in the
middle of the main patch to generate dual CP radiation. The
proposed antenna is printed on RT duroid substrate with
thickness 3.2mm, relative permittivity 2.33, loss tangent
0.019 and fed at probe feed point (F). The suggested fractal
slot antenna is depicted in Fig. 2.
Iteration 0
Index Terms — Circular polarization; Asymmetry;
WLAN bands; gain.
Iteration1
Indentation depth (D)
I. INTRODUCTION
Microstrip antennas are used in a wide range of
applications because of their low profile, low volume and
low cost advantages. In space applications the signal
changes its polarization arbitrarily when travelling through
ionosphere. To avoid loss of the signal due to this, special
antennas are preferred to radiate the signal in circular
polarization (CP).
Most of the single band circularly polarized antennas are
designed by introducing asymmetry in the structure using
slits along corners [1]-[3] and unbalanced slots on the patch
[4]-[6]. Dual band circularly polarized antennas are: stacked
patch [7], multiple U slots [8] on the patch etc. that are
reported earlier. However, designing dual band antennas
using fractal slot concept has not been adequately reported
in open literature. In this paper design of dual CP antenna
for WLAN 2.4 GHz and 5.8 GHz applications by employing
Minkowski fractal slot antenna is attempted.
Fig. 1. The generation of Minkowski fractal curve.
Dx
F
W2
Dy
L1
L2
Patch
II. ANTENNA GEOMETRY
Fractal geometries are generated from an original square
patch by the application of a generator method iteratively. A
Minkowski curve is generated as indicated in Fig. 1.The
straight line is divided into three equal sections. The central
section is replaced with some indentation depth (D). This
process is repeated to get higher iteration order fractal
Substrate
Probe feed
Fig. 2. The proposed fractal slot antenna.
III. RESULTS AND DISCUSSIONS
To excite two orthogonal modes of equal amplitude and
900 phase-shift for CP, the opposite sides of the square patch
are replaced with asymmetrical Minkowski fractal curves.
The end to end length (L1) of the patch is 36 mm. The
proposed antenna without fractal slot generates single CP
band at 2.4 GHz.
TABLE I
SUMMARIZED DIMENSIONS OF THE PROPOSED ANTENNA
Parameter
L1
L2
W2
F
Dimensions
(mm)
36
0.35*L1 =12.6
0.15*L1 = 5.4
(7,7)
Parameter
Value
Dx
Dy
0.22
0.11
To generate dual band CP operation an
asymmetrical fractal slot introduced in the middle of the
main patch. The generated second CP band is mainly
because of the embedded slot. The simulations are carried
out using commercial IE3D and HFSS electromagnetic
simulators and are depicted in Fig. 3. The first CP band at
2.4 GHz is mainly because of the strong current distribution
along the fractal curves of the main patch and for second
band it is along the fractal curves of the slot as shown in
Fig. 4. The simulated axial ratio plot is shown in Fig. 5. The
gain vs frequency plot is pictured in Fig. 6. It is observed
that proposed antenna provides more than 4-dBi gain at both
the CP bands. Dimensions of the antenna are given in Table
1.
Fig. 3. The simulated return loss characteristics of the proposed fractal antenna using HFSS and IE3D.
Axial ratio (dB)
5
4
3
2
1
0
0
(a)
(b)
Fig. 4 The simulated current distribution on the patch: (a) 2.4 GHz, and (b)
5.8 GHz.
2
4
Frequency (GHz)
Fig. 5 The axial ratio plot.
6
8
IV. CONCLUSIONS
7
6
A novel fractal slot antenna is proposed for WLAN
applications. Without using stacked patch technique two
bands are generated by the suggested asymmetrical fractal
structure. For the simulation of the designed structure IE3D
and HFSS electromagnetic simulators are employed. The
nominated antenna generates good circular polarization at
both the bands with 3-dB axial ratio bandwidths of 1.6%
and 3% respectively at 2.4 GHz and 5.8 GHz. The
simulation results show that the presented antenna designed
over a single layer substrate is very useful for WLAN.
Gain (dBi)
5
4
3
2
1
0
0
2
4
6
Frequency (GHz)
REFERENCES
[1]
Fig. 6 The Gain vs Frequency plot.
There is a deviation in the IE3D and HFSS
simulated return loss curves. However, IE3D assumes
default infinite substrate and ground plane, where as in
HFSS substrate and ground plane are finitely defined. So,
HFSS results are considered for bandwidth calculations. The
simulated 10-dB return loss and 3-dB axial ratio bandwidths
of the first band at 2.4 GHz are 10% and 1.6%, for second
band at 5.8 GHz they are 5.2% and 3% respectively. The
simulated radiation pattern of the proposed antenna at 2.4
GHz is depicted in Fig. 7.
[2]
[3]
[4]
[5]
[6]
[7]
[8]
Fig. 7. Radiation pattern at 2.4 GHz.
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