Antenna Array at 2.4 GHz for Wireless LAN system using Point To Point
Communication.
Mohamad Kamal A. Rahim, Mohd Nazri A. Karim, Thelaha Masri, Osman Ayop
Wireless Communication Center (WCC),
Faculty of Electrical Engineering,
Universiti Teknologi Malaysia,
81310 Skudai, Johor, Malaysia
Email: [email protected], [email protected], [email protected],
Abstract - This paper described the design of
microstrip patch antenna array operating at 2.4 GHz
for Wireless Video using point to point
communication system. The array of four by four
microstrip square patch antennas with inset feed
technique were designed, simulated, fabricated and
measured with the aid of microwave office software.
The simulation and measurement results are able to
operate in ISM band for point to point communication
system. The four by four arrays had a return loss of -8
dB with 16% bandwidth. The gain obtained from
measurement is 14 dBi with 30o half power beamwidth
(HPBW) for H plane and 28o for E Plane.
Keywords: Array Antenna, Microstrip Antennas, point to
point system, inset feed technique, corporate feed
1. Introduction
Wireless communication has experienced an
enormous growth since it allows users to access
network services without being tethered to wired
infrastructure. The two wireless system that have
experienced the most rapid evolution and wide
popularity are the standard developed by IEEE for
wireless local area network (WLAN) identified as
802.11 b,g which is operated in ISM band (2.4 GHz)
Point to point communication brings crucial
responsibility to antennas since they are expected to
provide the wireless transmission between those
devices [1]. Besides being able to indicate good signal
to noise ratio and immunity to noise, the antennas in
microwave links will have portray compact structure
and ease of construction to be mounted on various
devices.
In high performance point to point application where
size, weight, cost performance ease of installation are
constraints, low profile antenna is very much required
to meet these requirements, microstrip antenna is
preferred. Microstrip antenna technology began its
rapid development in the late 1970s. By the early
1980s basic microstrip antenna elements and arrays
were fairly well establish in term of design and
modeling [2]. In the last decades printed antennas have
been largely studied due to their advantages over other
radiating systems, such as light weight, reduced size,
low cost, conformability and possibility of integration
with active devices.
Although microstrip antenna has several
advantages like low profile, light weight and simple to
manufacture, it also has several disadvantages low
gain, narrow bandwidth with associated efficiency is
low. These disadvantages can however be overcome
with intelligent designs incorporated in whole antenna
structures. One of the ways to overcome these
problems is by constructing many patch antennas in
array configuration.
2. Planar Array Structure
The radiation pattern of a single element is relatively
wide and each element provides low values of
directivity (gain). In many applications, especially for
point to point communication system it is necessary to
design antennas with very directive characteristic (high
gain) to meet the demands of long distance
communication. This can be accomplished by
increasing the electrical size of the antenna [2]
Planar arrays are more versatile and can provide
more symmetrical pattern with lower side lobes. In
addition it can be used to scan the main beam of the
antenna toward any point in space. Figure 1 shows the
M x N element of the planar array structure. The array
factor can be written as
⎧ 1 sin (ψ x M / 2 ) ⎫⎧⎪ 1 sin (ψ y N / 2 )⎫⎪
AFn = ⎨
⎬⎨
⎬
⎩ M sin (ψ x / 2 ) ⎭⎪⎩ N sin (ψ y / 2 ) ⎪⎭
(1)
Where
ψ x = kd x sin θ cos φ + β x
ψ y = kd y sin θ cos φ + β y
The array factor is a function of the geometry of
the array and the excitation phase. By varying the
separation d and the phase β between the elements, the
characteristic of the array and the total field of the
array can be controlled. The planar arrays can control
the beam shape in both planes and form pencil beams.
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The total field of the array is determined by the vector
addition of the fields radiated by the individual
elements. This assumes that the current in each
element is the same as that of the isolated elements.
This is usually not the case and depend the separation
between the elements. To provide very directive
patterns, it is necessary that the fields from the
elements of the array interfere constructively (add) in
the desired direction and interfere destructively (cancel
each other) in the remaining space [2]. Ideally this can
be accomplished, but practically it is only approached.
In an array of identical elements, there are five
controls that can be used to shape the overall pattern of
the antenna.
network can be prohibitively large thereby reducing
the overall efficiency of the array. In this paper the
corporate feed with inset feed is being discussed for
the antenna array design.
(a) corporate feed
(b) series feed
Figure 2 Type of feed network in microstrip antenna
array [2]
3
Figure 1: Planar array geometries [2].
In general the radiation pattern of microstrip
antenna array can be determined once the aperture is
known. The amplitude and phase distribution at each
element is usually determined from the intended
application. Existing methods to feed microstrip arrays
can be categorized into parallel and series feed. The
parallel or corporate feed has a single input port and
multiple feed lines in parallel the output port. Each of
these feed lines is terminated at an individual radiating
element. The series feed usually consists of a
continuous transmission line from which small
proportion of energy are progressively coupled into the
individual element disposed along the line. The series
feed constitutes a traveling wave array if the feed line
is terminated in a matched load. Figure 2 shows the
difference between corporate feed and series feed for
microstrip antenna.
A corporate feed is most widely used parallel feed
configuration. For a uniform aperture distribution, the
power is equally split at each junction. However
different power divider ratios can be chosen to
generate a tapered distribution across the array. The
disadvantages of this type of feed is that it requires
long transmission lines between radiating elements and
the input port hence the insertion loss of the feed
Design consideration of 4 by 4 Microstrip
Patch Antenna Array
The design of the antenna array was started by
selecting the suitable patch shape of the antenna. The
square patch is chosen because it simplifies analysis
and performance prediction. This antenna has been
designed to operate at 2.4 GHz with input impedance
of 50 Ω, using FR4 (εr = 4.5) and height (h) of 1.6 mm.
The design starts with the simple rectangular
microstrip antenna with inset feed. Then, the
microstrip antenna is simulated using the Microwave
Office software. After the simulation, the microstrip
antenna is fabricated using FR4, with dielectric
constant (εr = 4.5) and height of 1.6 mm. Finally the
microstrip antenna is measured using the network
analyzer and the measured values are compared with
the simulated values.
The single element design is shown in figure 3. The
dimension of the patch is 29 mm x 29 mm with inset
feed at 8 mm. The width of the transmission line is 3
mm.
Figure 3: Single element rectangular patch antenna
The equation below is used to calculate the length and
width of patch antenna.
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L=
c
2 f ε eff
ε eff =
(2)
− 2∆l
ε r +1 ε r −1⎛
2
+
2
12 h ⎞
⎜1 +
⎟
w ⎠
⎝
−1 / 2
⎛w
⎞
0.412h(ε eff + 0.3)⎜ + 0.264 ⎟
h
⎝
⎠
∆l =
w
(ε eff − 0.258)⎛⎜ + 0.8 ⎞⎟
⎝h
⎠
w=
c
2 fr
2
1+ εr
(3)
Tee junction power divider and quarter wave
transformer impedance matching sections were used to
couple the power to each element for radiation. The
output line impedances Z1 and Z2 (the line for power
ratio) can then be selected to provide various power
divisions ratio. In this design the power ratio has been
selected so that the equal power transmission will be
obtained. Thus for 50 ohm input line a 3 dB power
divider can be made using two 100 ohm output lines.
(4)
(5)
L= the length of the patch antenna
4. Result and Discussion
Figure 5 shows the input return loss between
simulation and measurement. The simulation result
gives a return loss of -32 dB at 2.43 GHz while the
measurement results give a return loss of -32 dB at
2.56 GHz. The bandwidth for simulation and
measurement are between 16 % and 18%.
4x4 S11 square(S11)- measurement vs simulation
W = the width of the patch antenna
0
εeff = effective substrate
-5
∆l = fringing field of the antenna
Figure 4 shows the configuration of the 4 x 4
microstrip patch array antenna design at 2.4 GHz. A
coaxial feed is connected to the center of array from
the other side of substrate. Power divider and quarterwave transformer impedance matching sections are
used to couple the power to each element for radiation.
RL in dB
Since the square patch antenna has been used the
length and the width of the antenna is similar.
-10
-15
-20
-25
-30
-35
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
Freq in GHz
S11- measurement
S11- simulation
Figure 5: Input Return Loss of 4 x 4 microstrip patch
antenna array
Figure 6 (a) and (b) shows the E Plane and H Plane
measurement of radiation pattern. The co and crosspolar isolation is nearly 28 to 30 dB for E and H plane.
The half power beam width (HPBW) of the radiation
pattern is 28o and 30o respectively. The simulation and
measurement result show the pattern for E and H plane
is very similar even though the cross polar isolation
has a difference radiation pattern. The radiation pattern
for E plane is narrower compared to the H plane.
Figure 4: four by four microstrip patch antenna array
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4x4 S- E plane
0
-20
30
330
-30
-40
60
300
-50
-60
-70
90
-20
-30
-40
-50
27
-70
-60
-60
-50
-40
-30
-20
-60
-50
120
240
-40
-30
150
210
-20
180
E plane Co vs Degree
E plane Cross vs Degree
Figure 8 Gain comparison between monopole antenna at
2.4 GHz
(a) E Plane
4x4 S- H plane
5.
0
-20
30
Conclusion
330
-30
-40
300
60
-50
-60
-70
90
-20
-30
-40
-50
-60
27
-70
-60
-50
-40
-30
-20
-60
-50
120
240
-40
-30
150
210
-20
180
H plane CO vs Degree
H plane Cross vs Degree
(b) H Plane
Four by four (4 x 4) array of microstrip antenna with
inset feed technique has been designed simulated and
compared in this paper. It shows that the return loss
between the measurement and simulated are within the
frequency band that has been designed. The slightly
shifted frequency is due to the FR4 board that has εr
varies from 4.0 to 4.8. The return loss at – 10 dB
shows a good impedance matching occur between
simulation and measurement. The beam width
(HPBW) from simulation and measurement has a
value of nearly 28o to 30o. The gain obtained from
measurement is 8 dB more compared to monopole
antenna operating at the same frequency
Figure 6: Measurement of Radiation Pattern at 2.4 GHz.
Acknowledgement
Figure 7 shows the 3 D radiation pattern from CST
simulation software. It shows that the radiation pattern
is in the broadside of the antenna array
The authors thank to Ministry of Science Technology
and Innovation (MOSTI) for supporting the research
work, Research Management Centre (RMC), Wireless
Communication Centre Universiti Teknologi Malaysia
(UTM) for the support of paper presentation
References
Figure 7: 3 D Simulation radiation pattern
Figure 8 shows the gain comparison between
monopole antenna and the array antenna. It shows that
the gain of the antenna array is 8 dB more than the
monopole antenna. Theoretically if the monopole
antenna has a gain of 5 dBi, the gain of the antenna is
nearly 13 dBi.
[1] R.A. Saed and S. Khatun, “Design of Microstrip
Antenna for WLAN,” Journal of Applied
Sciences, Vol 5 (1), pp. 47 – 51, May 2005
[2] C.A. Balanis, Antenna Theory, Analysis and
design. 2nd ed. Hoboken, N. J, John Wiley & Sons,
2005
[3] D.M.Pozar, A Review of Aperture Coupled
Microstrip Antennas: History, Operation,
Development, and Applications, University of
Massachusetts: Article review, 1996
[4] Lu Wong, K. Planar Antennas for Wireless
Communications. Hoboken, N. J: John Wiley &
Sons.2003
[5] L. Setian. Practical Communication Antennas
with Wireless Applications.Upper Saddle River,
NJ: Prentice Hall, 1998
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