Design of a circularly polarized E-shaped patch antenna with enhanced bandwidth for 2.4 GHz WLAN applications

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Design of a circularly polarized E-shaped patch antenna with enhanced bandwidth for 2.4 GHz WLAN applications. This paper presents the design of a wideband circularly polarized E-shaped patch antenna for 2.4-GHz wireless local area networks (WLAN) applications. The proposed antenna is a modified form of the conventional circularly polarized E-shaped patch antenna.
VNU Journal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7
Design of A Circularly Polarized E-shaped Patch Antenna
with Enhanced Bandwidth for 2.4 GHz WLAN Applications
Hong Van Tam1, Luong Vinh Quoc Danh*,2
1Vinaphone Company, Vietnam
2Department of Electronics and Telecommunication Engineering,
College of Engineering Technology, Can Tho University, Vietnam
Abstract
This paper presents the design of a wideband circularly polarized E-shaped patch antenna for 2.4-GHz wireless
local area networks (WLAN) applications. The proposed antenna is a modified form of the conventional
circularly polarized E-shaped patch antenna. By incorporating additional slots into the antenna patch, the
impedance bandwidth and return loss of the circularly polarized antenna are improved by about 6.5% and 12 dB,
respectively. Measurements of the fabricated antennas show good agreement with simulated results.
© 2015 Published by VNU Journal of Science.
Manuscript communication: received 30 April 2014, revised 04 May 2015, accepted 25 June 2015
Corresponding author: Luong Vinh Quoc Danh, lvqdanh@ctu.edu.vn
Keywords: Axial Ratio, Circular Polarization, E-shaped Patch, WLAN.
1. Introduction
ratio bandwidth compared to the U-slot patch
Circularly-polarized antennas have been
employed in many modern wireless
communication systems such as navigation,
satellite communication systems, radio
frequency identification (RFID), WLAN and
WiMAX. One of the attractive advantages of
the circularly polarized antennas is that they can
reduce transmission loss caused by the
misalignment between antennas of transmitter
and receiver. In addition, circular polarization
provides better ability to combat multi-path
fading problem and thus enhances overall
system performance.
antennas. The design introduced in [1] has
provided a simple approach to achieve
circularly polarized radiating fields from a
single-feed microstrip antenna without the
necessity of it being square or comer-trimmed.
In [2], the size and position of the slots of the
E-shaped patch antenna have been tuned to
improve the impedance bandwidth and return
loss. The results from [2] have shown that the –
10 dB impedance bandwidth of about 21.6%
was obtained (2.28-2.81 GHz), with a lowest
value of S11 of –17.5 dB in the 2.4-2.5 GHz
band. The axial-ratio of this antenna was kept
below 3 dB in the 2.4 GHz WLAN band.
In [1], the authors have presented a
circularly polarized E-shaped patch antenna
with unequal slots that offers wideband axial
In this paper, we present the design of a
modified E-shaped patch antenna that offers
e
f
 
h
 
W
 
 
1
+
h
 
 
p
97.
2
H.V. Tam, L.V.Q. Danh / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7
wider impedance bandwidth and better return
circuits can be altered to extend the impedance
loss
compared
to
the
conventional
one.
By
bandwidth of the antenna.
properly incorporating additional slots to the E-
shaped patch, the impedance bandwidth and
return loss S11 of the proposed antenna are
improved by about 6.5% and 12 dB,
3. E-shaped Patch Antenna Design for 2.4
GHz WLAN Applications
respectively. The axial ratio remains below 3
dB in the 2.4 GHz WLAN band. Measurements
of the fabricated antennas show good agreement
with simulated results.
The initial parameters of the rectangular
microstrip patch antenna defined in [4] are used
in the first step of the design process.
The width W of the rectangular patch is:
2. Features of the E-shaped Patch Antennas
W
= 2fr
c
er +1
(1)
Fig. 1 presents the geometry of the
conventional E-shaped patch antenna [1] and
where fr is the resonant frequency of the
antenna.
the
modified
one.
As
shown
in
Fig.
1b,
The actual length L of the patch:
compared to the conventional E-shaped patch
antenna, the proposed antenna has 3 additional
slots incorporated into the patch. Two slots
having length of d1 and width of d2 are made on
the top and bottom arms of the E-shaped patch
L = c 2DL (2)
r reff
Extended length of the patch ΔL (according
to the Hammerstad formula):
and another slot having length of d3 and width
of d4 is added to the center of the patch. The
dimension and position of the slots are key
parameters in controlling the antenna
(ereff +0.3)W +0.264
DL = 0.412h
(ereff 0.258)h +0.8
(3)
bandwidth.
They
should
be
appropriately
Effective permittivity of the patch εreff :
chosen to obtain the achievable bandwidth.
The principle of the bandwidth
ereff = er2 1 + er2 1 1+12W 2
(4)
improvement can be explained using equivalent
circuits of the patch. Fig. 2 illustrates the
fundamental idea of the wideband mechanism
of the E-shaped patch antenna. The upper and
lower parts of the patch can be modeled as the
Coaxial-probe feeding is located at the
distance F from the edge of the patch:
F = y0 = 49.5cos1 1501 =16.4 (mm) (5)
L1C1
and
L2C2
resonant
circuits,
respectively
In the second step, we follow the design
[3]. When the additional slots are incorporated
procedure
described
in
[1]
to
simulate
and
into the lower and upper arms of the E-shaped
optimize the E-shaped patch antenna with two
patch, the values of L and C in the resonant
unequal slots for 2.4 GHz frequency band. As
circuits are changed. By tuning the length d1,
the
last
stage,
three
parallel
slots
are
width
d2
and
position
P1
of
the
slots,
the
incorporated into the E-shaped patch to improve
resonant feature of the L1C1 and L2C2 resonant
resonant
feature
of
the
patch
antenna:
two
H.V. Tam, L.V.Q. Danh / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7
3
identical slots are added to the upper and lower
from Fig. 3 and Fig. 4 that the dimensions of
arms of the E-shaped patch; and one small slot
the two slots in the upper and lower arms of the
is cut at the middle of the patch. The target of
patch
keep
an
important
role
in
widening
this
step
is
(a)
to
extend
the
impedance
impedance bandwidth of the antenna. They are
bandwidth of the antenna and simultaneously
symmetrically
placed
about
the
y-axis
to
maintain the axial-ratio level below 3 dB over
maintain the orthogonality of currents on the
the desired frequency band, and (b) to align the
patch. Besides, the third slot cut at the center of
axial-ratio and impedance bandwidths together.
the patch can be used to control the level of
Dimensions and positions of the additional slots
return loss S11, as presented in Fig. 5 and Fig. 6.
are tuned to meet the design goal. It can be seen
D
(c)
Fig. 1. Geometry and dimensions of the E-shaped patch antenna: (a) the conventional form,
(b) the proposed antenna, and (c) side view of the antenna.
Fig. 2. Resonance mechanism of the E-shaped patch antenna.
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Design of a circularly polarized E-shaped patch antenna with enhanced bandwidth for 2.4 GHz WLAN applications. This paper presents the design of a wideband circularly polarized E-shaped patch antenna for 2.4-GHz wireless local area networks (WLAN) applications. The proposed antenna is a modified form of the conventional circularly polarized E-shaped patch antenna..

Nội dung

VNU Journal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7 Design of A Circularly Polarized E-shaped Patch Antenna with Enhanced Bandwidth for 2.4 GHz WLAN Applications Hong Van Tam1, Luong Vinh Quoc Danh*,2 1Vinaphone Company, Vietnam 2Department of Electronics and Telecommunication Engineering, College of Engineering Technology, Can Tho University, Vietnam Abstract This paper presents the design of a wideband circularly polarized E-shaped patch antenna for 2.4-GHz wireless local area networks (WLAN) applications. The proposed antenna is a modified form of the conventional circularly polarized E-shaped patch antenna. By incorporating additional slots into the antenna patch, the impedance bandwidth and return loss of the circularly polarized antenna are improved by about 6.5% and 12 dB, respectively. Measurements of the fabricated antennas show good agreement with simulated results. © 2015 Published by VNU Journal of Science. Manuscript communication: received 30 April 2014, revised 04 May 2015, accepted 25 June 2015 Corresponding author: Luong Vinh Quoc Danh, lvqdanh@ctu.edu.vn Keywords: Axial Ratio, Circular Polarization, E-shaped Patch, WLAN. 1. Introduction Circularly-polarized antennas have been employed in many modern wireless communication systems such as navigation, satellite communication systems, radio frequency identification (RFID), WLAN and WiMAX. One of the attractive advantages of the circularly polarized antennas is that they can reduce transmission loss caused by the misalignment between antennas of transmitter and receiver. In addition, circular polarization provides better ability to combat multi-path fading problem and thus enhances overall system performance. In [1], the authors have presented a circularly polarized E-shaped patch antenna with unequal slots that offers wideband axial ratio bandwidth compared to the U-slot patch antennas. The design introduced in [1] has provided a simple approach to achieve circularly polarized radiating fields from a single-feed microstrip antenna without the necessity of it being square or comer-trimmed. In [2], the size and position of the slots of the E-shaped patch antenna have been tuned to improve the impedance bandwidth and return loss. The results from [2] have shown that the – 10 dB impedance bandwidth of about 21.6% was obtained (2.28-2.81 GHz), with a lowest value of S11 of –17.5 dB in the 2.4-2.5 GHz band. The axial-ratio of this antenna was kept below 3 dB in the 2.4 GHz WLAN band. In this paper, we present the design of a modified E-shaped patch antenna that offers 2 H.V. Tam, L.V.Q. Danh / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7 wider impedance bandwidth and better return circuits can be altered to extend the impedance loss compared to the conventional one. By bandwidth of the antenna. properly incorporating additional slots to the E-shaped patch, the impedance bandwidth and return loss S11 of the proposed antenna are improved by about 6.5% and 12 dB, respectively. The axial ratio remains below 3 dB in the 2.4 GHz WLAN band. Measurements of the fabricated antennas show good agreement with simulated results. 3. E-shaped Patch Antenna Design for 2.4 GHz WLAN Applications The initial parameters of the rectangular microstrip patch antenna defined in [4] are used in the first step of the design process. The width W of the rectangular patch is: 2. Features of the E-shaped Patch Antennas W = 2fr er +1 (1) Fig. 1 presents the geometry of the conventional E-shaped patch antenna [1] and where fr is the resonant frequency of the antenna. the modified one. As shown in Fig. 1b, The actual length L of the patch: compared to the conventional E-shaped patch antenna, the proposed antenna has 3 additional slots incorporated into the patch. Two slots having length of d1 and width of d2 are made on the top and bottom arms of the E-shaped patch and another slot having length of d3 and width of d4 is added to the center of the patch. The dimension and position of the slots are key parameters in controlling the antenna bandwidth. They should be appropriately L = c − 2ΔL (2) r reff Extended length of the patch ΔL (according to the Hammerstad formula): (ereff +0.3)W +0.264 ΔL = 0.412´h (ereff −0.258) h +0.8 Effective permittivity of the patch εreff : chosen to obtain the achievable bandwidth. The principle of the bandwidth ereff = er2 1 + er2 1 1+12W −2 (4) improvement can be explained using equivalent circuits of the patch. Fig. 2 illustrates the fundamental idea of the wideband mechanism of the E-shaped patch antenna. The upper and lower parts of the patch can be modeled as the L1C1 and L2C2 resonant circuits, respectively Coaxial-probe feeding is located at the distance F from the edge of the patch: F = y0 = 49.5cos−1 1501 =16.4 (mm) (5) In the second step, we follow the design [3]. When the additional slots are incorporated procedure described in [1] to simulate and into the lower and upper arms of the E-shaped patch, the values of L and C in the resonant optimize the E-shaped patch antenna with two unequal slots for 2.4 GHz frequency band. As circuits are changed. By tuning the length d1, the last stage, three parallel slots are width d2 and position P1 of the slots, the incorporated into the E-shaped patch to improve resonant feature of the L1C1 and L2C2 resonant resonant feature of the patch antenna: two H.V. Tam, L.V.Q. Danh / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7 3 identical slots are added to the upper and lower arms of the E-shaped patch; and one small slot from Fig. 3 and Fig. 4 that the dimensions of the two slots in the upper and lower arms of the is cut at the middle of the patch. The target of patch keep an important role in widening this step is (a) to extend the impedance impedance bandwidth of the antenna. They are bandwidth of the antenna and simultaneously symmetrically placed about the y-axis to maintain the axial-ratio level below 3 dB over the desired frequency band, and (b) to align the axial-ratio and impedance bandwidths together. Dimensions and positions of the additional slots are tuned to meet the design goal. It can be seen D maintain the orthogonality of currents on the patch. Besides, the third slot cut at the center of the patch can be used to control the level of return loss S11, as presented in Fig. 5 and Fig. 6. (c) Fig. 1. Geometry and dimensions of the E-shaped patch antenna: (a) the conventional form, (b) the proposed antenna, and (c) side view of the antenna. Fig. 2. Resonance mechanism of the E-shaped patch antenna. 4 H.V. Tam, L.V.Q. Danh / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7 w Fig. 3. Simulated results of return loss S11 at different values of d1 while other parameters are fixed. Fig. 6. Simulated return loss S11 at different values of d4 while other parameters are fixed. The optimized dimensions of the proposed antenna are determined through parametric analysis, and are listed in Table I. Antenna simulations are performed using the ANSYS High FrequencyStructure Simulator (HFSS) [5]. TABLE I THE DIMENSIONS OF THE PROPOSED CIRCULARLY POLARIZED E-SHAPED PATCH (IN MM). L W h F Ws Ls1 Ls2 47.5 77 10 12.75 4 16.5 44 P P1 23.5 11.5 d1 d2 d3 d4 Lg Wg 16.5 7 2.5 6 110 150 Fig. 4. Simulated results of return loss S11 at different values of d2 while other parameters are fixed. Fig. 5. Simulated return loss S11 at different values of d3 while other parameters are fixed. The calculated far-field 2-D and 3-D radiation patterns of the antenna at 2.44 GHz are plotted in Fig. 7. It can be seen that the half-power beam width of the designed antenna is about 60 degrees. The calculated peak gain of the antenna is 9.7 dBi at the center of the 2.4 GHz WLAN band. The simulated return loss S11 results are depicted in Fig. 8, where the return loss of proposed antenna is improved by about 12 dB compared to that of the conventional E-shaped patch antenna in [2]. It can also be seen from Fig. 9 that the calculated axial-ratio of the designed antenna remains below 3 dB in the 2.4 GHz WLAN band. It is worth noting that the H.V. Tam, L.V.Q. Danh / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7 5 return loss of the conventional antenna can be improved further. However, this improvement will lead to the reduction of the 3-dB axial ratio bandwidth of the antenna. Comparisons of the left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) patterns in the xz plane at 2.44 GHz are shown in Fig. 10. The current distribution on the E-shaped patch of the proposed antenna is presented in Fig. 11. Fig. 8. Comparison of return loss S11 between the conventional E-shaped patch antenna (dash line) and the proposed antenna (solid line). (a) Fig. 9. Comparison of axial ratio between the conventional E-shaped patch antenna (dash line) and the proposed antenna (solid line). 4. Experimental Results (b) Fig. 7. Simulated (a) 2-D and (b) 3-D radiation patterns of the proposed antenna at 2.44 GHz. A prototype of the proposed antenna was fabricated and measured. The front view of the antenna prototype is shown in Fig. 12. Fig. 13 shows the measured return loss S11 of the proposed antenna (dash lines) compared to the simulated ones (solid lines). As shown in 6 H.V. Tam, L.V.Q. Danh / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7 Fig. 13, throughout the WLAN frequency band (2.42-2.484 GHz), the values of S11 are better than – 22.5 dB. The lowest value of S11 of about –31 dB was obtained at 2.42 GHz. The measured results agree well with the simulated ones. Measurements were performed using the Anritsu Antenna Analyzer S331D. In order to verify the antenna performance in practical applications, the designed antenna was connected to the antenna connector of a commercial 2.4-GHz WLAN access point (D-Link DIR-600) serving as a transmitter, and a laptop computer was employed as a receiver. The NetStumbler software [6] installed on the Fig. 11. Current distribution on the patch of the proposed antenna. computer was used to measure the WLAN signal strength transmitted from the access point. The measurements were carried out under non-line-of-sight condition. It can be seen from Fig. 14 that the proposed antenna greatly improves WLAN signal reception compared to that of the 2-dBi omnidirectional one. Performance comparisons between the two E-shaped patch antennas are summarized in Table II. Fig. 12. Front view of the prototype of the proposed E-shaped patch antenna. Table II Antenna Performance Comparison Fig. 10. The radiation patterns of left-hand circular polarization (red) and right-hand circular polarization (blue) in the xz plane. Parameters Impedance bandwidth Lowest value of S11 Axial-ratio bandwidth Peak gain Conventional E-shaped patch antenna [2] 21.62% (2.28 ÷ 2.81 GHz) –17.5 dB 2.72% (2.41 ÷ 2.48 GHz) 9.7dBi The proposed antenna 28.15% (2.24 ÷ 2.93 GHz) –30 dB 4.1% (2.38 ÷ 2.48 GHz) 9.7dBi H.V. Tam, L.V.Q. Danh / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 31, No. 2 (2015) 1-7 7

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