PIERS Proceedings, Hangzhou, China, March 24-28, 2008
208
Design and SAR Measurement of the Trapezoidal Shape Antenna
S. W. Lee1 , S. M. Park1 , N. Kim1 , S. W. Park1 , and S. Y. Rhee2
1
Chungbuk National University, Korea
Chonnam National University, Korea
2
Abstract— In this paper, we designed the trapezoidal shape antenna which can be used in
WLAN services. The trapezoidal shape would be working in the 2 GHz band and 5.2 GHz,
and the small rectangular pieces in the trapezoidal shape were making the frequency shift from
5.2 GHz to 5.7 GHz. In addition, we found out the best values of the antenna parameters by
sweeping some characteristics. The designed antenna has occurred resonances of which the first
band is 1.65 GHz ∼ 2.36 GHz and the second band is 5.49 GHz ∼ 5.88 GHz below the return loss of
−10 dB. Also, we will measure the SAR (Specific Absorption Rate) values for the human body.
1. INTRODUCTION
For the minimized antenna, there are the methods of using the semiconductor, the geometrical
structures, and sub-patches [1]. One of research trends is dramatically downsized the antenna using
the mictrostrip feeding method and supplemented the radiation using the patch until now, but it
would be increased the current density and Q factor (quality factor) by the minimized antenna and
seriously decreased the bandwidth of the frequency range. The other way, the impedance would be
increased, and then the gain of the antenna should be decreased [2]. CPW (coplanar waveguide)
feeding slot antenna is studied various methods for increased the working bandwidth of the antenna,
and there are designed several structures by following the application field [3]. CPW feeding slot
antenna is smaller the radiation loss and the dispersion than the microstrip method, and we can
take the broad bandwidth because the varying of the characteristic impedance is small [4–11].
In this paper, we designed the antenna which makes dual resonances interposed the patch that
is the teeth of a saw in the CPW feeding antenna of the trapezoidal shape having the small size and
the broadband characteristics. The designed antenna is working the dual band, 1.65 GHz∼2.36 GHz
and 5.49 GHz∼5.88 GHz, for the PCS, WCDMA, and WLAN services. In addition, we proved the
designed antenna is satisfied the SAR guideline.
2. ANTENNA DESIGN
Figure 1 illustrates the antenna structure of the trapezoidal shape. The size of the designed
antenna is 60.0 mm(W)×30.0 mm(L)×1.0 mm(T), and the substrate is FR4 consisted of the copper
of 1 mm and dielectric constant of 4.62. The antenna structure is CPW structure of the basic
trapezoidal shape, as shown Fig. 1. Usually most of the patch antenna has the rectangular shape,
but we proposed the trapezoidal shape antenna showed the broadband characteristics by making
the smoothly flowing of the current [5]. Although we can get the broadband characteristics in the
trapezoidal shape antenna transformed the rectangular shape, we cannot get the characteristics of
the adopted band. So there is deleted the wasted portion without approximately 1 mm of the width
in the antenna. Therefore, there are dual resonances in the frequency bands of 2 GHz and 5.2 GHz.
Various parameters shown Figure 1 and Table 1 are changed so that the resonance is formed in
the desired frequency band. In the trapezoid patch, the desired band characteristic was obtained
in a 2 GHz band, but 5.2 GHz was just obtained in the band for WLAN. Therefore, the frequency
band could be manipulated according to the length of the patch by inserting another patch having
a rectangular shape in the trapezoid patch. As already know, the wavelength is in an inverse
proportion to the frequency, and thus the length of the patch should be shortened in order to
increase the frequency. This will be described in detail in “Chapter 3. Antenna Simulation,”
afterwards, but the frequency band satisfying a PCS service and WCDMA service in the range of
1.65 GHz to 2.36 GHz could be obtained through sweeping the parameters of the antenna, and the
frequency band of 5.49 GHz to 5.88 GHz, which satisfies the WLAN service band, could be obtained
by adding a saw-like patch.
The parameters shown in Table 1 represent values optimized through sweeping. However, in
an initial design stage, the width of the strip line was acquired by the use of factors, including a
Progress In Electromagnetics Research Symposium, Hangzhou, China, March 24-28, 2008
209
Table 1: Parameters of the proposed antenna.
Parameters
Explanation
Value (mm)
po1x
po2x
py
sh
gx
gy
sx
sy
The base of the trapezoid patch
The upper side of the trapezoid patch
The height of the trapezoid patch 0
The size of the sub-patch
The width of the ground plane
The height of the ground plane
The width of the feeder
The length of the feeder
16
26
14
1
28.84
4
1.8
10
permittivity, the thickness of a substrate, the thickness of a metal, a desired frequency band, and
an impedance line width between the strip line and a ground was acquired.
Figure 2 shows a simulated result using the optimized values shown in Table 1. On the basis of a
return loss of −10 dB or less, a first resonance occurred in the band of from 1.65 GHz to 2.36 GHz,
and a second resonance occurred in the band of from 5.49 GHz to 5.88 GHz. Figure 3 shows
radiation patterns of the designed antenna in 1.67 GHz and 5.5 GHz. In this thesis, a trapezoid
CPW antenna, usable in the PCS, WCDMA and WLAN bands, was designed. The overall size of
the antenna was reduced by the use of a CPW structure and its performance was checked through
simulation. As a result of the simulation of the designed antenna, we could determine that the dual
resonance was formed, and the antenna satisfied the band of 1.65 GHz to 2.36 GHz and 5.49 GHz
to 5.88 GHz.
S-Parameter Magnitude in dB
0
s1,1
-10
-20
-30
0
1
2
3
4
5
6
7
Frequency / GHz
Figure 1: The structure of the proposed antenna.
Figure 2: The return loss of the optimized parameters.
3. ANTENNA FABRICATION AND SAR MEASUREMENT
We were fabricated the proposed antenna, as shown Figure 4. For the measuring of the absorption
of the electromagnetic wave in the human body, we were doing SAR (specific absorption rate)
measurement. The target service is WLAN of 2.45 GHz band, and we have got the results of 1g
and 10 g averaged SARs in 2.45 GHz, as shown Figure 5.
As the results of the SAR measurement, 1 g averaged SAR, which the guideline is 1.6 W/kg,
is 0.529 W/kg, and 10 g averaged SAR, which the guideline is 2.0 W/kg, is 0.273 W/kg. The SAR
values are satisfied the guideline values.
PIERS Proceedings, Hangzhou, China, March 24-28, 2008
210
Figure 3: The radiation pattern at 1.67 GHz and 5.5 GHz.
Figure 4: The fabricated antenna.
Figure 5: The SAR measurement.
4. CONCLUSIONS
We designed and fabricated the antenna of the trapezoid shape for the PCS, WCDMA, and WLAN
bands in this paper. We reduced the antenna size using the CPW structure, and confirmed the
performance using the computer simulation firstly. Then we fabricated the proposed antenna having
the dual resonance characteristic. In the return loss of −10 dB or less, the antenna was working
the 1.65 GHz to 2.36 GHz and 5.49 GHz to 5.88 GHz. In case of SAR measurement, the 1 g and
10 g averaged SARs are satisfied the guideline which is 1.6 W/kg and 2.0 W/kg respectively. As the
results, the 1 g and 10 g averaged SARs are 0.529 W/kg and 0.273 W/kg. We proved all results are
satisfied the guideline by the experiment test.
ACKNOWLEDGMENT
This research was supported by the MIC (Ministry of Information and Communication), Korea,
under the ITRC (Information Technology Research Center) support program supervised by the
IITA (Institute of Information Technology Advancement) (IITA-2007-(C1090-0701-0034)).
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