2 x 1 Rectangular-Patch Antenna Array at 2.4 GHz
JEANETTE MEJIA ROJAS1, MARIO REYES-AYALA1,
EDGAR ALEJANDRO ANDRADE-GONZALEZ1, SANDRA CHAVEZ-SANCHEZ2, HILARIO
TERRES-PEÑA2, RENE RODRIGUEZ-RIVERA2
1Department of Electronics, 2Department of Energy
Metropolitan Autonomous University
San Pablo 180, Col. Reynosa Tamaulipas, Azcapotzalco (ZIP 02200), Mexico City
MEXICO
Abstract: - In this paper a microstrip antenna array is carried out. The array has two rectangular patches in a linear
2 x 1 array. This work includes the design, simulation, implementation and evaluation of both, a single radiator
and the linear two rectangular microstrip antenna array. The antenna array was designed and built for low-cost
and noncomplex manufacturing techniques, because the array is dedicated for educational purposes in under-
graduate radiocommunication courses at Metropolitan Autonomous University. The mechanical tolerance in the
structure dimensions is around 0.2 mm, that is easy to be obtained by an inexpensive CNC or very well-known
optical techniques. The simulation and optimization of the array was computed using HFSS and the results of
this stage include antenna patterns and the reflection coefficient (S11). Besides, the experimental evaluation of
the array is quite similar to the simulations results in both, radiation patterns and the frequency response using
the matching interval, for a single radiator and the 2x1 array.
Key-Words: - Array antenna, microstrip, rectangular patch, reflection coefficient, antenna pattern, antenna
bandwidth, matching network, return loss.
Received: May 23, 2022. Revised: March 9, 2023. Accepted: April 20, 2023. Published: May 8, 2023.
1 Introduction
Many modern radio-communication systems use
array antennas, due to some important advantages.
Cellular and broadcasting communication systems
have coverage areas that can be changed over time.
In this scenario, a flexible antenna pattern is more
practical with a single-radiator antenna [1], [2]. The
power of a single element of a antenna array can be
multiplied by a factor. The antenna array sums the
single radiators contributions in a vectorial result. If
the coverage area is changing, the radiation pattern of
the array can be adjusted manually or employing a
control system. The time used in a new setup
configuration is narrowed down significantly and can
be modified dynamically in more complex systems
[2], [3], [4].
Antenna arrays can also identify the direction of
several sources in space with the aim to improve the
quality of service in Personal Communication
System (PCS). As a example of this, 4G and 5G uses
2D and 3D spatial discrimination, by using planar
and tri-dimensional antenna arrays in the base
stations. Moreover, the channel capacity can be
increased using these types of antennas [1]. [2], [3],
[6], [7].
The microstrip radiator was selected as a single
radiator in the array, because it is compatible with
planar surfaces and it has low-cost implementation.
The rectangular microstrip is one of the simplest
geometries and is normally presented in
radiocommunication and antenna under-graduate
courses. A small set of variables are involved in
rectangular, circular and triangular geometries if are
chosen for the patch of the single-radiator.
2 Antenna Array design
The design of the antenna array is divided into two
parts, single or primary radiator and the 2x1 array
including the matching network.
2.1 Primary radiator design
A rectangular microstrip antenna can be approximate
using the Munson procedure, that has been improved
and expanded over the years. In this method, the
patch radiator is modeled by a microstrip
transmission line, that normally needs a matching
technique, see Fig. 1. Other matching techniques uses
LCR circuits or shunt stubes implemented by
transmission lines [5], [6], [7], [8], [9], [10], [11].
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Jeanette Mejia Rojas, Mario Reyes-Ayala,
Edgar Alejandro Andrade-Gonzalez,
Sandra Chavez-Sanchez, Hilario Terres-Peña,
Rene Rodriguez-Rivera
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Fig.1 Geometry of rectangular patch antenna.
The design procedure begins with the width of the
patch in the top layer of the Printed Circuit Board
(PCB), see equation (1).
(1)
Where W is the width of the rectangular patch, m;
fr is the resonant frequency in the dominant mode,
Hz;
0 is the vacuum permeability, H/m;
0 is the
vacuum permeability, F/m;
r is the dielectric
constant of the substrate; and, v0 is the vacuum phase
velocity of the light, m/s. The flux lines of the electric
and magnetic fields do not remain between the patch
and the ground plane, because the flux lines are
curved in the edges of the patch. This problem causes
an inhomogeneous media, the substrate of the PCB
and air. In order to get a good approximation, it is
necessary to obtain an effective dielectric constant
reff that has an intermediate numerical value in
comparison with the PCB substrate and air, see
equation (2).
(2)
Where
r is the dielectric constant of the substrate;
and, h is the thickness of the substrate, m. The curved
flux lines of the electromagnetic field introduce
another problem, because the antenna behavior looks
like if the length were greater. The equation (3)
determines the extension of the length.
(3)
Where
L is the length increment, m; and, h is the
thickness of the substrate, m. Then the actual length
of the patch is determined by equation (4).
(4)
Where L is the actual length of the patch, m; and
Leff is the effective length of the patch, m; see
equation (5).
(5)
Where
is the wavelength in the propagation
media, m. In order to optimize the power transfer, it
is necessary to calculate the antenna impedance, see
equations (6), (7) and (8).
(6)
(7)
(8)
Where G is the patch conductance,
0 is the
vacuum wavelength, m; and, c is the phase velocity
of light in the vacuum, m/s. It is important to see that
equation (7) is an asymptotic approximation. In this
paper the feeding line transmission was calculated
using a quarter wavelength transformer.
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Fig.2 Rectangular patch antenna with a microstrip
line transmission feed.
2.2 Antenna array and matching network
design
The linear rectangular-patch antenna array has two
rectangular patches and their 50 transmission lines
in the top layer of the PCB, where it must be placed
the phase center of the array. In this case the
matching network was implemented width
microstrip line transmissions as is illustrated in
the Fig. 2. The matching network is symmetrical
because the patches have identical geometries,
and it is built with a 100 T-patch, two 70.71
quarter wave-length transformers and a 50
microstrip line transmission.
Fig.3 Rectangular patch antenna array with the
matching network.
3 Problem Solution
Using the procedure described before, the resulting
dimensions of the primary radiator are summarized
in the Table 1 and can be shown in Fig. 4.
[mm]
Approximation
Optimized
Width
W
38.393
38.393
Length
L
29.798
29.1
Feeder
width
Wf
0.1596
0.18
Feeder
length
Lf
18.667
10.0
Table 1. Rectangular patch antenna.
Fig.4 Rectangular patch antenna with a microstrip
line transmission feed.
Employing this information, the rectangular patch
radiator was simulated with the HFSS (High
Frequency Structure Simulator) software package,
that is a full-wave simulator based on Finite Element
Method (FEM).
The initial model of this structure is illustrated in
Fig. 5 in HFSS software. This model can be improved
in the computation tool, because the model was
calculated with empirical formulas. In fact, the
numerical method in HFSS (Finite Element Method
FEM) has a good approximation in this kind of
antenna.
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Fig.5 Model of the rectangular patch radiator.
The Fig. 6 shows the return loss of the rectangular
patch after the optimization stage. In order to obtain
a resonant frequency of 2.4 GHz, the optimized
model was employed.
Fig.6 S11 parameter of the optimized model of the
rectangular patch.
The performance of the radiator in the space is
completed with the 3D and polar antenna patters that
are illustrated of the Fig. 7 and Fig.8, respectively.
Fig.7 3D radiation pattern of the optimized model of
the rectangular patch.
Fig.8 Polar antenna pattern of the optimized model
of the rectangular patch.
The primary radiator was built using optical and
chemical techniques. The optimized model in HFSS
was exported and printed, see Fig. 9.
Fig.9 Exported file used in primary radiator
fabrication.
The primary radiator was built using optical and
chemical techniques. The optimized model in HFSS
was exported and printed, see Fig. 9. The single
radiator built with optical and chemical methods is
illustrated in the Fig. 10.
2.00 2.10 2.20 2.30 2.40 2.50 2.60 2.70 2.80
Freq [GHz]
-14.00
-12.00
-10.00
-8.00
-6.00
-4.00
-2.00
0.00
dB(S(WavePort1,WavePort1))
Ansoft Corporation HFSSDesign1
XY Plot 3
m1
m2 m3
Curve Info
dB(S(WavePort1,WavePort1))
Setup1 : Sw eep1
Name X Y
m1 2.3960 -13.0818
m2 2.3650 -9.9655
m3 2.4300 -9.9905
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Fig.10 Single radiator of the array.
The rectangular patch radiator was measured
using a near-field scanner (RFX RFxpert by
EMSCAN) and a network analyzer. This kind of
equipment computes a far-field antenna pattern by
interpolation of the near field detected with a set of
sensors placed below the scanner surface. The
scanner is compatible with planar microstrip
antennas, and it is necessary to place the bottom layer
of the PCB over the scanner, see Fig. 11 and Fig.12.
Fig.11 Single radiator measurement using a near-
field scanner.
Fig.12 Near-field measurement in progress with the
single-radiator.
The main results obtained with the Network
Analyzer (NA), a Personal Computer (PC) and the
near field scanner can be appreciated in Fig. 13. The
software of the scanner shows the far field obtained
by interpolation, see Fig. 14. The PC uses the ethernet
port to control the NA and the near-field scanner.
Fig.13 Experimental result of S11 parameter for the
single-patch radiator.
Fig.14 Radiation pattern of the primary patch.
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Using the design procedure that was described in
the Section 2, the main features of the antenna array
is presented in Table 2. The initial model of the
antenna array that was used in the HFSS simulation
is presented in Fig. 15.
[mm]
Initial
Optimized
Patch width
W
38.3934
38.3934
Patch length
L
29.1
29.1
Left patch width
Wf1
0.18
0.18
Right patch length
Lf1
10.0
10.0
50 Ω Tx line width
Wf2
3.0029
2.9756
50 Ω Tx line length
Lf2
17.2913
7.0
70.71 Ω Tx line width
Wf3
1.5969
1.5595
70.71 Ω Tx line length
Lf3
17.7066
17.7499
100 Ω Tx line width
Wf4
0.70325
0.6672
100 Ω Tx line length
Lf4
18.1467
9.07364
50 Ω main Tx line width
Wf5
3.0029
2.97561
50 Ω main Tx line length
Lf5
17.2913
32.0220
Table 2. Main features of the antenna array.
Fig.15 Initial model of the antenna array.
The return loss of the optimized model of the
antenna array are plotted in Fig. 16, where the S11 is
used in logarithmic scale.
Fig.16 S11 parameter of the antenna array obtained
by simulation.
The antenna patterns of the optimized model of
the antenna array are shown in Fig. 17 and 8, for both
tri-dimensional and polar diagrams, respectively.
Fig.17 3D antenna pattern of the array.
Fig.18 Polar antenna pattern of the optimized
antenna array.
2.00 2.10 2.20 2.30 2.40 2.50 2.60
Freq [GHz]
-40.00
-35.00
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
dB(S(WavePort1,WavePort1))
Ansoft Corporation HFSSDesign1
XY Plot 1
m1
m2 m3
Curve Info
dB(S(WavePort1,WavePort1))
Setup1 : Sw eep1
Name X Y
m1 2.2950 -38.9971
m2 2.1230 -9.9035
m3 2.5710 -10.0217
-10.80
-7.60
-4.40
-1.20
90
60
30
0
-30
-60
-90
-120
-150
-180
150
120
Ansoft Corporation HFSSDesign1
Radiation Pattern 1
m1
Curve Info
dB(DirTotal)
Setup1 : LastAdaptive
Freq='2.4GHz' Phi='0deg'
dB(DirTotal)
Setup1 : LastAdaptive
Freq='2.4GHz' Phi='90deg'
Name Theta Ang Mag
m1 360.0000 -0.0000 0.5365
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The antenna array was fabricated using the
printing file that is shown in Fig. 19. This file was
exported from HFSS in DXF format, which is one of
the most compatible AUTOCAD files.
Fig.19 HFSS exported file used in the array.
The antenna array was built using very well-
known optical and chemical methods. The final
appearance of the antenna array can be seen in the
Fig. 20.
Fig.20 Antenna array that was built and evaluated
by experimental methods.
Employing the same approach that was used in the
single-radiator, antenna array was evaluated by near-
field measurement. The EMSCAN scanner was
controlled using ethernet ports from a PC, see the
Figure 21.
Fig.21 EMSCAN Scanner configuration used in the
measurement of the antenna array.
The far-field interpolation calculated by the
EMSCAN is illustrated in the Fig.22 and 23, where
tridimensional and polar antenna diagrams were
plotted.
Fig.22 Tri-dimensional antenna pattern obtained
using the EMSCAN scanner.
Fig.23 Polar antenna pattern obtained using the
EMSCAN scanner.
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Finally, the return loss of the rectangular-patch
antenna array was obtained using the FieldFox
Network Analyzer, see the Fig.24.
Fig.24 S11 parameter obtained using the EMSCAN
scanner.
A comparison of simulation and experimental
results is shown in Table 3, where HFSS row is
related to the optimized model of the antenna array.
Resonant Frequency
[GHz]
Bandwidth [%]
HFSS
2.3960
2.7128
FieldFox RF
Analyzer
2.3750
1.8947
Table 3. Comparison of simulation and
experimental results.
4 Conclusion
A 2x1 rectangular patch antenna array was designed,
simulated, optimized, built and evaluated, for 2.4
GHz band application. This antenna is already used
in radiocommunication undergraduate courses at
Metropolitan Autonomous University. The antenna
was designed in order to be built using low-cost
materials and techniques, like optical and chemical
methods. The PCB selected for the antenna is the FR-
4 substrate with a thickness around 1.544 mm. The
HFSS software package was used in the simulation
and optimization procedures. The antenna array it is
now improved with weighting factor in the single-
radiator elements of the array, with the aim to identify
the source direction in a 2-D coverage area structures
[12], [13], [19].
Experimental and simulation results are quite
similar, where narrowband feature is obvious, due of
usage of rectangular patches in the single radiator
role structures [14], [15], [17].
At this time a software is in construction in order
to obtain a computational tool to compute the antenna
layouts, including the matching network. It is
possible to improve the antenna arrays if the
matching network uses a LCR circuits, because the
radiation efficiency normally is reduced with
microstrip transmission lines. The features of the
single radiator can be increased using a broadband or
multi-band defected [16], [18], [20],[21]. Besides the
work presented here is the first stage of a set of
antennas in spatial discrimination with some kinds of
apertures [22], [23].
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Jeanette Mejia Rojas, Mario Reyes-Ayala,
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Sandra Chavez-Sanchez, Hilario Terres-Peña,
Rene Rodriguez-Rivera
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and Propagation, Vol. 2022, 2022.
Jeanette Mejia Rojas
Formal analysis,
investigation,
methodology, writing –
original draft
Mario Reyes-Ayala
Conceptualization,
investigation formal
analysis,
writing, review and
editing
Edgar Alejandro
Andrade-Gonzalez
Project administration,
resources, review,
validation
Sandra Chavez-
Sanchez
Visualization, review
validation
Hilario Terres-Peña
Supervision, validation,
review
Rene Rodriguez-Rivera
Validation, review
This work was supported by the research project
EL002-18 in the Metropolitan Autonomous
University in Mexico City.
Conflicts of Interest
The authors have no conflicts of interest to declare
that are relevant to the content of this article.
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