Comparison between Straight and U shape of Ultra Wide Band
Microstrip Antenna using Log Periodic Technique
Mohamad Kamal A Rahim, Mohamad Nazri Abdul Karim, Thaleha Masri, Azhari Asrokin
Wireless Communication Centre, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310
UTM Skudai Johor, Malaysia.
matching techniques to improve the bandwidth ratio without
Abstract
This paper described the design, simulation and
fabrication of the Ultra Wideband (UWB) antennas for straight
and U shape using seventeen elements log-periodic (LP)
technique. The antennas have been modeled using microstrip
lines and S parameter data from individual single element. The
data is extracted from the momentum simulation and combined
with the microstrip transmission line. The properties of antennas
such as bandwidth return loss and radiation pattern have been
investigated and compared between simulation and
measurements. A bandwidth for UWB antenna is achieved using
seventeen element arrays. The cross-polar isolation of the UWB
antenna is in the range 8 to 20 dB for straight shape. The typical
half power bandwidth (HPBW) of the UWB antenna is 40
loss of its radiation pattern properties [4 - 8].
In the past, one serious limitation of the microstrip antenna
was its narrow bandwidth characteristics, being 15 to 50%
that of commonly used antenna elements such as dipoles,
that
wavegus ans emnt s
as was
slots, and waveguides horns [9]. This limitation was
successfully removed achieving a matching impedance
bandwidth ratio it was necessary to increase the size, height,
volume or feeding and matching techniques [10]. Logperiodic is one of the techniques has been investigated and
used successfully by previous researchers [11 12] to enhance
.
.
.
.
the bandwidth of microstrip antenna.
Furthermore, the return loss of the antenna is above -10 dB from
both simulation and measurement..
Index Terms
UWB antenna, microstrip antenna, wideband
antenna, log periodic.
II. DESIGN CONSIDERATION FOR UWB ANTENNA
The design principle for UWB antenna using LP technique
requires scaling of dimensions from period to period so that
performance is periodic with the logarithm of frequency. This
principle can be applied to an array of patch antennas. The
patch length (L), the width (W) and Inset (I) are related to the
scale factor Xc by Eq. 1.
UWB short-range wireless communication, which makes
use of data transmission in the 3.1 - 10.6 GHz frequency
band, is different from a traditional carrier wave system. A
UWB system sends very low power pulses, below the
transmission noise threshold. In UWB communications, the
antennas are significant pulse-shaping filters. A UWB antenna
is a non-resonant low-Q radiator whose input impedance
remains constant over a wide-band operating frequency [1].
T
Any distortion of the signal in the frequency domain
(filtering) causes distortion of the transmitted pulse shape,
thereby increasing the complexity of the detection mechanism
at the receiver [2].
Although current research works have been focused in
omni-directional UWB antennas [3], directional UWB
antennas are also recently having research interest. As it is
well known, a directional antenna concentrates the energy into
a narrow solid angle compared with an omni-directional
antenna; and generally, it requires being relatively large in
size compared to the omni-directional one. Before the decade
1990's, all the proposed UWB antennas were based on
general volumetric structures [3]. From 1992, several
microstrip, slot, and planar monopole antennas with simple
structure such as circular, elliptical or trapezoidal shapes have
been proposed. Today the state of art of UWB focuses in these
microstrip, slot and planar monopole antennas with different
Lm+i
=
-
Lm
WM+1
Im+1
Wm
'm
(1)
If the dimensions of the array is multiplied by Xc it scales
into itself with element m becoming element m+l, element
m+I becoming element m+2 etc. this self-scaling property
implies that the array will have the same radiating properties
at all frequencies that are related by a factor of -c. A single
element of rectangular or square geometry as shown in Fig. 1
can be designed for the lowest resonant frequency using
transmission line model.
The value of L, W and I can be found through equations in
[11, 12]. This value will be scaled into log periodic element.
Calculation of design parameters for UWB and compact
UWB antennas using log-periodic technique are shown in
Table 1. The substrate used is FR4 with dielectric constant of
47adhih f16m.tesaigfco c=10.Tels
tnetomarils0.01. Eaheeethsbe iuae
truhmmnu
iuainuigAietAS h
1-4244-0521-1/07/$20.OO ©2007 IEEE
696
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parameter of these elements has been combined into the
...
circuit element
TABLE 1
DESIGN PARAMETER FOR UWB ANTENNA
W=L
Im (mm)
22.993
21.898
20.856
19.862
18.917
18.016
17.158
16.341
15.563
14.822
14.116
13.444
12.803
12.194
11.613
11.072
10.544
12.493
11.898
11.331
10.792
10.278
9.788
9.322
8.878
8.455
8.053
7.669
7.304
6.956
6.625
6.310
6.01
5.724
Freq.
(GHz)
3.03
3.18
3.34
3.51
3.69
3.87
4.06
4.27
4.48
4.70
4.94
5.19
5.45
5.72
6.00
6.29
6.61
(mm)
4
dm
Rin (50Q)
23.640
19.429
16.667
15.482
14.014
10.996
20.162
26.504
12.985
21.852
13.833
15.668
13.914
12.227
11.268
12.204
15.834
7.698
7.341
7.002
6.788
6.510
6.257
5.997
5.555
5.294
5.055
4.827
4.610
4.403
4.207
4.020
4.05
3.663
(mm)
W=L
U shape of UWB antenna
(b)
(
Fig. 2: UWB prototype antenna of seventeen elements using log
periodic technique
III. RESULTS AND DISCUSSION
A.
Return Loss Measurement and Simulation
The measurement and simulation result of return loss for
the UWB antenna is shown in Fig. 3 and 4. Figure 3 shows
the radiation pattern for U shape of UWB antenna while
figure 4 shows the return loss for straight shape of UWB. The
bandwidth from the measurement result is achieved around
98% for UWB antenna. The experimental results show the
frequency up by 7%. The resonance of the antennas can be
seen by observing the dip in the return loss. There is a close
agreement between the simulation and measurement result for
the bandwidth. The return loss for both design give a similar
response for simulation and measurement.
>
-'
L=W Xt
(mm)
Xi
3mlane
1.6mm
Fig. 1: Square microstrip with inset feed
-10
Fig. 2 shows the fabrication layout of the seventeen elements for
straight and U shape of UWB antenna.
mm
1
-50~~~~~~~~~~~
___Momentum
___Measurement
(GHz)
~~~~~~~~~~~~~~~~~~~~~~~~~~~Frequency
-
Figure 3 Simulation and Measurement of Return Loss for
U shape type
(a)
straight shape of UWB antenna
697
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Frequency 5 GHz, E Plane
Comparison
3.5
2.5
6.5
5.5
4.5
cross polar
60
120
2
7.5
30
-5
-1a0
|
100
1
E-2021
5
-
XB-
0/
0
30
-25
-30
a270
-Measurementradiation_pattern_for_the_UWB
-35
(c)
frequency (GHz)
E Plane
Fig. 4: Simulation and Measurement for Straight shape UWB
Frequency 7 GHz E Plane
030
120
B
at 5 GHz
-
polar
-6-Figure |5 cross
Radiation
pattern for straight1shap
copolar
crsWpoar
10
Radiation Pattern Characteristic
Fig. 5 shows the radiation pattern for the UWB antenna at
frequencies. The radiation pattern is in the broadside
direction. At lower frequency 3.5 GHz the cross-polar
isolation for B plane is 8.5 dB. The HPBW at this frequency is
20P0 Pfor B plane. The measurement at the middle frequency 5
B plane
GHz shows that the cross-polar isolation
>1 ¢ for
S>---)
><e)is te19.19
dB. The HPBW at this frequency is 15poPOfor B plane.
two
Frequency 3
1
40
60
520
240
co
(d)
polar
cross
270
E Plane
at
7
GPt
Figure 5 Radiation pattern for straight shape UWB antenna
polar
30
18
isolation of the antenna at the broadside is higher. The
~~~~~~~~~~~polar
periodic antenna. At 3 GHz frequency band the
0
240
0
(a) E Plane at 3.5 i-GHz---t-----°0 S5~?
Frequency 4 GHz, E Plane
90
40
120-
co
polar
cross
polr
-
30~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~0
20
1690
2
co
and
cross
beam is slightly tilt form the broadside direction. At 5 GHz
frequency band the co and cross polar of the antenna is very
low in the broadside direction. Comparing with the straight
0shape it shows that the co polarization of the straight shape is
much better compared to the U shape of the log periodic
antenna at most of the frequencies
2130
180
n
periodic antenna. At 3 GHz frequency band the co and cross---
(
GHz. E Plane
90
120
csf
~~~~~~~~~~30
240 3~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~0~~~~~~4
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--
---
ACKNOWLEDGEMENT
E Plane at 4.15GHz
:,=~~~~~~~~~~~~~~~~~~~~3
.
>1
The authors thank to Ministry of Science Technology and
/ \ J \\Innovation (MOSTI) for supporting the research work,
Research Management Centre (RMC)
Communication Centre Universiti Teknologi
for the support of paper presentation.
and
Wireless
Malaysia (UTM)
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(b
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E Plane at 7 Ghz
[10]
[11]
Figure 6 Radiation pattern for U shape of UWB antenna
[12]
IV. CONCLUSION
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[13] M.K.A.Rahim, M.R. Ahmad, A. Asrokin, M.Z.A.A. Aziz 'The
Design of UWB antenna using log Periodic Technique'
Loughbrough Antennas and Propagation Conference (LAPC
A UWB antenna using seventeen elements log-periodic
(LP) technique has been designed, simulated, fabricated, and
tested successfully. A bandwidth up to 98% is achieved by
using seventeen element arrays for UWB antenna. The crosspolar isolation of the UWB antenna is in the range 8 to 20 dB.
The half power beamwidth of the UWB antenna is 40PoP for E
plane. The comparison between the straight shape and the U
2006), 2nd - 3rd April 2006, Loughbrough, U.K
shape of the log periodic antenna is investigated. It shows that
the straight shape has better co polarization at all frequency
range.
699
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