Compact Fractal Based UWB Band Notch Antenna

ISSN: 2312-7694
Muhib et al, / International Journal of Computer and Communication System Engineering (IJCCSE), Vol. 2 (5), 2015, 676-681
676 | P a g e
© IJCCSE All Rights Reserved Vol. 02 No.05 Oct 2015 www.ijccse.com
Compact Fractal Based UWB Band Notch Antenna
Muhib Ur Rahman
Deptt. Of Electrical Telecommunication Engineering
Military College of signals MCS, National University of Sciences and Technology, NUST
Rawalpindi
Abstract--- A compact Microstrip fed planar UWB
monopole antenna with band notch features is
proposed. The proposed design consist of rectangular
radiating patch with impedance steps and fractal slots
in the partial ground plane. Wide-band matching is
obtained by using the stair cased radiating patch and
fractal slots in the partial ground plane. A slot is
inserted in the radiating patch to reject 5/6 GHz WLAN
band. The antenna designed has low VSWR and
advantageous radiation pattern in the desired band.
The proposed antenna is printed on FR4 substrate and
is simulated in CST Microwave studio. The results has
been verified using Ansoft (HFSS). The design antenna
has a compact size of (30×36mm2
).
Index Terms- Fractal, stair case radiating patch, UWB
(ultra-wide band), UWB notch antenna
I. INTRODUCTION
The frequency band from 3.1 GHz to 10.6 GHz has
been allocated by the Federal Communications
Commission (FCC) for UWB wireless communication
applications. As UWB is the most promising technology
for future short range wireless communication [1]. The
advantages of UWB communication are that they offer
more resistance to multipath phenomenon, high data rate
short range wireless communication, low complexity and
low emission power. Antenna is the important part of UWB
system. The antenna required must have an omnidirectional
and stable radiation pattern and high radiation efficiency
[2].
The problem that encounters is that the IEEE 802.11a
WLAN system operates in 5.15 to 5.825 GHz band which
generate potential interference with the UWB
communication. This interference can be avoided by using
a good filtering techniques. But the filtering techniques is
much expensive and increases the system complexity. So
by designing antenna having band notch features is the
most simple and economical solution [3]. Various band-
notched UWB antennas have been developed for UWB
wireless communication. There are various techniques to
design band notch antennas such as etching L-shaped, E-
shaped, C-shaped, arc shaped and U-shaped slots on the
radiating patch [4-8]. Also there is another technique which
uses parasitic strips in the printed monopole [9].
In this paper, compact planar UWB antenna is analyzed and
simulated. The proposed rectangular patch antenna
parameters are calculated based on transmission line modal
analysis [10] and the detailed geometry and parameters are
shown in figures and tables. The antenna with non-uniform
impedance steps and fractal slots in the ground plane can
cover the entire UWB frequency band without rejecting
WLAN band. First the antenna results has been analyzed
with and without fractal slots in the partial ground plane.
Then we have analyzed the antenna results with and
without notch, by introducing slot in the radiating patch. A
slot in the radiating patch is inserted to notch the 5/6 GHz
WLAN band without affecting its gain. The antenna
designed has high gain, stable radiation pattern and best
matching in the desired frequency band.
II. ANTENNA GEOMETRY
The configuration of the proposed UWB antenna having
band notch characteristics is shown in Fig 1(a). This
antenna covers the entire UWB range while rejecting the
WLAN band. The antenna is fed with a 50 Ω microstrip
line and is constructed on FR4 substrate having thickness
(h) 1.6 mm, relative permittivity of 4.4 and tanδ =0.0025
which has dimensions of 30×36mm2
(Wsub × Lsub ). The
distance between ground plane and radiating patch (s) is
kept 1mm.The dimensions of the design are as follows:
Wsub =30mm, Lsub =36mm, Wp =15mm, Lp =16.5mm,Lgnd
=12.5mm, Lf =13.5mm, Wf =3mm, S=1mm.
Dimensions of fractal slots in the ground plane:
X=2.4mm, Y= any side of the solid curve =0.8mm,
Z=distance b/w fractal slots in the ground plane=11.2mm
Dimensions of stair cased impedance steps:
M N O P Q
1.25mm 1.25mm 2.5mm 1.6mm 2.5mm

ISSN: 2312-7694
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Dimension of slot:
Lxx Lyy Wxx Wyy
11.5mm 7mm 0.5mm 0.5mm
Front view showing dimensions of Patch and Substrate:
Fig 1(a)
Ground Plane with Fractal slots:
Fig 1(b)
Stair case impedance steps
Fig 2(a)
Fractal slots
Fig 2(b)
Slot in Patch
Fig 2(c)
III. RESULTS AND DISCUSSIONS
3.1. UWB antenna without slot-- First the antenna has
been designed without fractal slots in the ground plane. The
S11 plot shows that the antenna cannot cover the entire
UWB band and is matched to the transmission line only
from 3.1 to 7.7 GHz
Fig 3(a)
So we must enhance the impedance bandwidth of the
antenna. This is achieved by increasing electrical path
length for the surface current. To increase the electrical
path length for surface current distribution two similar
fractal slots are etched on top edge of the ground
plane. So by increasing the electrical path length for surface
current the impedance bandwidth in turn enhances [11, 13].
The fractal geometry has been introduced in the ground
plane as shown in Fig 2(b). The distance between these two
3 4 5 6 7 8 9 10 11 12
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-15
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-5
Frequency/GHz
Magnitudeofs11(db)

ISSN: 2312-7694
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slots, (Z) is adjusted to achieve the required UWB
frequency range. Impedance Matching has been found at
Z= 11.2mm and S =1mm which is the gap between the
radiating patch and the ground plane. The S11 curve shows
that the antenna now covers the entire UWB frequency
band and a maximum value of -25db at 6.65 GHz.
Fig 3(b)
The VSWR curve shows that antenna has no mismatch in
UWB band as VSWR < 2 in the entire band and a
maximum VSWR of 1.67 at 9.1 GHz.
Fig 3(c)
3.2. UWB antenna with slot-- By inserting slot in the
radiating patch, the antenna operate in the entire UWB
band while rejecting WLAN signal. The slot geometry is
shown in the Fig 2(c). Now there is no more potential
interference of the UWB and WLAN signals. The length of
the notch band is calculated from the equation (1) below:
fnotch =
𝐶
2×𝐋 √
Ԑr+1
2
(1)
Where, L is the length of the slot, ϵr is the relative
permitivity and C is the speed of light. The length of the
slot resonator is calculated from (1) while its position is
analyzed from surface current distribution as shown in Fig
4. The width of the slot is optimized by simulating at
different slot width as shown in Fig 3(a). The resonator will
introduce high reflection at resonance which will lead to
band notching effect. The length (Lxx and Lyy) of the slot is
the important parameter in notching the desired band. The
antenna is simulated at different slot widths as shown in Fig
3(a).
From the simulation at different slot width we select the
width of the slot =0.5mm. It is cleared from the VSWR
curves that the antenna has a very small effect by changing
the slot width, so we can choose any value of the above.
The important factor to consider over here is only the
length of the slot.
Fig 3(a)
So, by introducing the slot of length and width discussed
above in the radiating patch, the VSWR in the 5/6 GHz
WLAN band is greater than 2, which shows that the
antenna performance is not good in this band. The position
and effect of the slot is analyzed from surface current
distribution and transmission model analysis.
Ansoft HFSS simulations-- The antenna results has been
verified using Ansoft HFSS (2013). The verified results has
been plotted in Fig 3(b) and Fig 3(c). The S11 and VSWR
plot has been analyzed first with and without fractal slots in
the partial ground plane and then analyzed with and
without notch in the radiating patch. These results shows
that there is one notch band at 5/6 GHz WLAN band. A
very small difference is observed between the results
simulated through CST and HFSS.
3 4 5 6 7 8 9 10 11 12
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-12
-10
-8
-6
Frequency/GHz
Magnitudeofs11(db)
3 4 5 6 7 8 9 10 11 12
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
2.8
3
Frequency/GHz
voltagestandingwaveratio(vswr)
3 4 5 6 7 8 9 10 11 12
1
1.5
2
2.5
3
3.5
Frequency (GHz)
VSWR
vswr at slot width=0.5

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Fig 3(b)
Fig 3(c)
3.3 Surface current distribution-- Fig 4(a) shows the
simulated current distributions on the surface of the
proposed antenna at 4.1, 5.5, 7.7, and 8.5GHz. At 4.1, 7.7,
and 8.5 GHz, the current flows along the microstrip feed
line, while low current densities around the slot. On the
other hand, the surface current distribution on the antenna
at 5.5 GHz is concentrated around the slot.
Fig 4(a): Simulated current distributions on the surface of
the proposed antenna at different frequencies.
3.4 Radiation patterns
The simulated Far field radiation pattern of the proposed
antenna at different frequencies is shown in Fig 4(b). The
radiation pattern shows that no ripples are present at higher
frequencies.
3 4 5 6 7 8 9 10 11 12
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Frequency (GHz)
S-parameterMagnitude(db)
S11 with fracal slot and without Notch
S11 with fracal slot and Notch
S11 without fracal slot and Notch
3 4 5 6 7 8 9 10 11 12
1
1.5
2
2.5
3
3.5
Frequency (GHz)
VSWR
VSWR with fractal slot and without notch
VSWR with fractal slot and Notch
VSWR without fractal slot and Notch

ISSN: 2312-7694
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Figure 4.(b) Simulated far field radiation pattern of the
proposed antenna at different frequencies
IV. TIME DOMAIN RESPONSE
This section considers the communication between
the two designed UWB band-notched antennas. The
two antennas are designed and the distance between
the transmitting and the receiving antennas is kept
60cm, which is almost 6 wavelengths of the
considered band of operation at the lowest frequency.
Also we consider that the antennas are at the far field
of each other. Now by exciting the transmitting
antenna with different input pulses such as modulated
Gaussian pulse, first order Rayleigh pulse, fifth
derivative of Gaussian pulse and fourth order
Rayleigh pulse.
We also consider that the antennas operate in two
orientations: (a) face to face and (b) side by side as
shown in Fig 5. Fig 6 shows the transfer function, S12
versus the frequency in two different orientations. By
analyzing the figures it is clear that the transfer
function of face to face orientations is better than that
of side by side.
The correlation coefficient for the signal at the
terminals of the receiving antenna S2(t) and the input
signal S1(t) is determined by the relation used as
follows:
Where Ϯ is a delay that can be varied to make the
numerator maximum. The values of the correlation
coefficients calculated for each mentioned antenna are
given in Table below. These values shows the superiority
of the designed antenna over previous ones.
Fig 5(a) Face to Face
Fig 5(b) side by side
Correlation coefficient (ρ)
Type of
antenna
10 cm 60 cm
Antenna
without
Notch
0.9266 -0.926
Antenna
with
Notch
0.9011 -0.864

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Fig 5: Transmitting and Receiving antennas in two
different orientations
Fig 6: Frequency Vs. S21 Plot
V. CONCLUSIONS
A compact wide band rectangular radiating patch
antenna along with fractal slots in the partial ground
plane has been proposed. Wide band matching is
achieved by introducing fractal slots in the partial
ground plane and non-uniform stair cased impedance
steps at the radiating patch. The potential interference
between the UWB system and WLAN band has been
minimized by introducing slot in the radiating patch,
which reject the WLAN band. The antenna results
has been analyzed showing high average gain and
good radiation pattern. The antenna provides low
VSWR in the frequency band from 3 to 10.6 GHz
with a band-notching effect at the frequency band
from 5/6 GHz. The antenna has a compact size which
make them as a good candidate for UWB portable
devices.
REFERENCES
[1] Naghshvarian Jahromi, M. (2008). Compact
UWB bandnotch antenna with transmission-line-
fed. Progress In Electromagnetics Research B, 3,
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[2] Low, Z. N., Cheong, J. H., & Law, C. L. (2005).
Low-cost PCB antenna for UWB
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Letters, IEEE, 4, 237-239.
[3] Xu, J., Shen, D. Y., Wang, G. T., Zhang, X. H.,
Zhang, X. P., & Wu, K. (2012). A small UWB
antenna with dual band-notched
characteristics. International Journal of Antennas
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S. (2008, May). Designing an UWB patch antenna
with band notched by using L-shaped slot and
unsymmetrical feedline. In Electrical and Computer
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Conference on (pp. 000101-000104). IEEE.
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Wideband Printed Monopole Antenna with Reduced
Ground Plane and Band Notch
Characterization. Session 3P8, 733.
[6] Chu, Q. X., & Yang, Y. Y. (2008). A compact
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[7] Wong, K. L., Chi, Y. W., Su, C. M., & Chang, F.
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[8] Cho, Y. J., Kim, K. H., Choi, D. H., sik Lee, S.,
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[9] Kim, K. H., Cho, Y. J., Hwang, S. H., & Park, S.
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[10] Garg, R. (Ed.). (2001). Microstrip antenna
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[11] Hong, T., Gong, S. X., Liu, Y., & Jiang, W.
(2010). Monopole antenna with quasi-fractal slotted
ground plane for dual-band applications. Antennas
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[12] Karmakar, A., Banerjee, U., Ghatak, R., &
Poddar, D. R. (2013, February). Design and analysis
of fractal based UWB monopole antenna.
InCommunications (NCC), 2013 National
Conference on (pp. 1-5). IEEE.
[13] Falconer, K. (2013). Fractal geometry:
mathematical foundations and applications. John
Wiley & Sons.
[14] CST Microwave Studio Suite, CST Inc., 2014.
0 2 4 6 8 10 12
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Frequency (GHz)
MagnitudeS21(dB)
Face to Face
side by side

Compact Fractal Based UWB Band Notch Antenna

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