Design of a Dual Band 2.45 GHz and 5.2 GHz Microstrip MIMO
Antenna with T-Geometry based on AMC Reflector
SERAP KILINC EVRAN1, OZLEM COSKUN2
1Department of Electronics and Communications Engineering,
Namık Kemal University,
Faculty of Corlu Engineering,
TURKEY
2Department of Electrical-Electronics Engineering,
Suleyman Demirel University,
Faculty of Engineering and Natural Sciences,
TURKEY
Abstract: - Multiple input-multiple output (MIMO) is one of the important applications of WLAN wireless
communication technology. In wireless communication systems, especially with the developing services, an
increase in data speed and access quality is required in indoor WLAN systems for multi-media data
transmission. In new-generation wireless communication systems, high transmission performance and high data
rates can be achieved with MIMO systems that use multiple antennas in the sender and receiver. In the MIMO
system, parallel data transmission can be made over multiple antennas at the same time and frequency by using
the spatial domain. In this study, a MIMO dual-band microstrip antenna with artificial magnetic conductive
surface T geometry operating at 2.45 GHz and 5.2 GHz was designed. CST simulation program was used in the
designs. To increase the efficiency of antenna parameters; an artificial magnetic conductor design (AMC) was
made and used as a reflector for the antenna. The designed dual-band MIMO microstrip antennas; parameters
such as reflection coefficient, radiation diagrams, and gain were examined.
Key-Words: - Multiple Input-Multiple Output (MIMO); 2.45-5.2 GHz; Microstrip Antenna; AMC structure;
Performance Analysis; Wi-Fi.
1 Introduction
MIMO communication systems act as a savior due to
the increasing number of users and data
communication traffic in recent years. The most
important feature of MIMO technology is that it can
increase channel capacity and reliability without
requiring additional power or bandwidth, [1]. For
this reason, it has played a major and critical role in
communication systems with 4G communication.
MIMO systems are based on the use of multiple
channels on both the transmitter and receiver side. In
this way, it is possible to increase a limited capacity
by using multiple channels. Additionally, diversity
gain is achieved thanks to multiple antennas used in
both the transmitter and receiver.
In MIMO systems, signal attenuation is
overcome by using transmitter and receiver antennas
thanks to diversity methods, [2]. Multiple input-
multiple outputs (MIMO) technology, which
attracted the attention of researchers to eliminate
many problems such as limited channel capacity that
emerged in the 4th generation technology, has
become the focus of attention of researchers with 5G.
The most important reason why MIMO technology
has become the center of attention with 5G is that it
has multiple communication channels, and the
channel capacity can be easily increased, as well as
having important features such as broadband, high
data rate, high gain and low energy consumption, [3],
[4].
In the antenna structures of 5G technology,
traditional microstrip patch antennas are one of the
most preferred antenna structures due to their
features such as simple structure, easy use, and wide
variety. Despite these advantages, the most important
problem in the use of microstrip patch antennas is
their limited operating performance (bandwidth,
gain, etc.). With 5G, the use of MIMO structures is at
the forefront to increase the operating performance
of microstrip patch antennas, [5], [6], [7], [8]. With
MIMO antenna structures, important parameters of
Received: August 27, 2023. Revised: July 13, 2024. Accepted: August 19, 2024. Published: September 5, 2024.
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Serap Kilinc Evran, Ozlem Coskun
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the antenna such as bandwidth, radiation, and gain
can be improved, [9].
Artificial magnetic conductor (AMC), for a
specified frequency band is a type of electromagnetic
band gap material or artificially designed material
with a magnetic conductive surface. AMC is also
known as a high-impedance surface and has received
significant attention in recent years. The high
impedance feature and phase reflection within a
certain frequency range make AMC surfaces unique.
Such surfaces can be used to increase the bandwidth
and radiation performance of an antenna and reduce
its size, [10], [11], [12].
AMC benefits from both the suppression of
surface waves and the unusual reflection phase. This
can be applied to a variety of antenna designs,
including patch antennas, which are often affected by
the effects of surface waves. AMC surfaces have
very high surface impedance in a certain limited
frequency range where the tangential magnetic field
is small even with a large electric field across the
surface, [13]. The AMC surface can serve as a new
ground plane for low-profile wire antennas, which is
desirable in many wireless communications. Thus, to
reduce antenna size, the high-impedance surface
structure acts as a perfect magnetic conductor
(PMC), which does not exist in nature. Since its
structure is artificially designed, it is called an
artificial magnetic conductor. The AMC or PMC
state is characterized by the frequency or frequencies
at which the magnitude of the reflection coefficient is
1. The surface impedance (𝑍𝑠) is high and reflects
external electromagnetic waves without phase
reversal. AMC can also be used as a metallic plate,
such as a ground plane, to direct back radiation and
provide protection for antennas, [14].
In this study, a MIMO dual-band microstrip
antenna with artificial magnetic conductive surface T
geometry operating at 2.45 GHz and 5.2 GHz will be
designed.
2 Simulation Program and Material
Used
For the design of the dual-band microstrip antenna,
features such as the type of material to be used,
antenna geometry, dimensions, and operating
frequencies were determined. After these features
were decided, a T geometry antenna working in a
microstrip dual band was designed using the CST
Microwave Studio simulation program. The material
used for the microstrip antenna is FR4. Table 1
shows the properties of FR4 material.
Table 1. Properties of FR4 material
Material
Dielectric
constant
Lost
tangent
Dielectric
thickness
FR4
4.6
0, 0035
1, 6 mm
3 Artificial Magnetic Conductor
Design
In this study, the artificial magnetic conductive
surface was designed for the 2.4 GHz – 5.2 GHz
frequency bands, which are the operating frequencies
of the T microstrip antenna, and it shows magnetic
conductive surface properties in these band ranges.
Here, an artificial magnetic conductor was used as
the reflective surface. Since artificial magnetic
conductive surfaces have high resistance 180° phase
difference is observed in the reflected wave. For this
reason, there is no need to leave a distance of λ⁄4
between the radiating elements and the reflector. The
gap in this design; The distance up to λ/6 for 5.8
GHz and λ/15 for 2.45 GHz is 8 mm. For the T
microstrip antenna, each cell is 26*26 mm² in size
and there is a 1 mm gap between them. AMC grid
structure consists of 3*3 unit cells.
AMC reflector simulation pictures are shown in
Figure 1. The number of unit cells was chosen to
give the best performance with a small profile. The
AMC was then placed under the MIMO microstrip
antenna as a reflector.
Fig. 1: AMC reflector simulation image for T
microstrip antenna
The reflection phases graph of the AMC reflector
is shown in Figure 2.
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Fig. 2: Simulated reflection phases graph for AMC
reflector structure
4 T Geometry Microstrip Antenna
Design
A high-isolation microstrip MIMO antenna with T
geometry dual-band operating at 2.45 GHz and 5.2
GHz resonance frequencies is proposed. There are T-
shaped emitter elements on the upper side of the
dielectric material, as shown in Figure 3. The long
arm of the T shape is 17 mm, this value is a quarter
wavelength of 2.4 GHz frequency; The short arm
length of the T shape is about 4.8 mm, at this value
the quarter wavelength of 5.2 GHz is the square root
ratio of the dielectric constant of 4.5, taking into
account the effect of the dielectric material on the
length. Radiating elements are placed in sequential
rotation. This type of arrangement creates high
insulation between elements.
Fig. 3: Simulation image and dimensions of the T
antenna
The dimensions of the antenna were designed so
that the long side of the T is 4.8 mm and the short
side is 17 mm. In this way, it is possible to operate at
two different frequencies. The dimensions of the
bottom layer of the microstrip antenna are designed
to be 16 * 22 mm. When the antenna is supported by
a PEC ground, the distance between the PEC ground
and the irradiating element is 28 mm, which is a
quarter wavelength at 2.4 GHz. With the AMC
surface, the air gap of the antenna can reduce the
height and the radiation characteristics can be
improved.
Figure 4 shows the antenna printed circuit. There
is an AMC reflector under the antenna. This air gap
is 8 mm, which is approximately λ/8 at 5.2 GHz and
λ/15 at 2.4 GHz. Two identical T antennas are placed
at a rotation angle of 90° relative to each other. This
method has been optimized with the CST simulation
program to have high insulation without using the
method mentioned above.
Fig. 4: Printed circuit of the T-geometry microstrip
antenna operating at 2.45 GHz and 5.2 GHz with
AMC reflector
5 T Geometry Microstrip Antenna
Simulation Results
Simulation results of the designed T-geometry
microstrip dual-band MIMO antenna are given. For
the designed T geometry antenna; The reflection
coefficient (S11) and isolation parameter (S21)
simulation results of the antennas used with different
reflectors were compared graphically. In Figure 5, it
is observed that the simulation results of the
parameter S11 which is the reflection coefficient of
the T geometry antenna with AMC reflectors, are -15
dB for 2.45 GHz and -18 dB for 5.2 GHz. Since they
are below the value of -10 dB, these are the operating
frequencies.
Fig. 5: S11 simulation result of AMC reflector
antenna
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In Figure 6, the graph of the simulation results of
the S11 parameter of the antenna is given
comparatively for different reflectors. The red line
shows the results of the AMC antenna, the pink line
shows the results of the microstrip antenna, and the
brown line shows the results of the PEC antenna.
These values are -15 dB for 2.45 GHz, -17 dB for 5.2
GHz with the AMC reflector; in the case of PEC
structure -11 dB for 2.45 GHz, -14 dB for 5.2 GHz;
In the case without the reflector, it is -12 dB for 2.45
GHz and -15 dB for 5.2 GHz.
Fig. 6: S11 simulation results of the antenna with
different reflectors
Figure 7 shows the insulation results of the
antenna with different reflectors. In the case of a
PEC reflector, it is -20 dB for 2.45 GHz and 5.2
GHz, and for an antenna without reflector, it is -20
dB for 2.45 GHz and 5.2 GHz. MIMO antennas must
have good isolation. For good isolation, the S21
parameter should be above -20 dB. According to this
graph, the AMC antenna shows a better isolation
performance than other antennas. In the case of the
AMC reflector, it is -24 dB for 2.45 GHz and -23 for
5.2 GHz. Since the S21 isolation value is below -20
dB at resonance frequencies, it is understood that the
isolation between MIMO antenna elements is good.
The important factor in this value is that two
identical T antennas are placed at a 90° angle relative
to each other.
Fig. 7: S21 simulation results of the antenna with
different reflectors, green line AMC antenna, black
line microstrip antenna, red line PEC antenna
Figure 8 shows the frequency-standing wave
ratio change graph of the T microstrip antenna with
the AMC reflector. Standing wave ratio; It occurs
when the outgoing and reflected signals meet, and its
disadvantage is that it causes power loss on the
antenna. Therefore, a value below two is the desired
value. As can be seen from the graph, the resonance
frequencies of the antenna have values of 1.5 at 2.45
GHz and 1.1 at 5.2 GHz.
Fig. 8: Frequency-standing wave ratio graph of T
microstrip antenna with AMC
Figure 9 and Figure 10 in Appendix show the 2D
far field pattern results for the T microstrip antenna.
As seen in Figure 9 (Appendix), for 2.45 GHz, the
maximum radiation angle of port 1 is 23° and the
signal level is 8.3 dBi; The signal level of port 2 is
8.08 dBi and its maximum radiation angle is 15°.
From Figure 10 (Appendix), for 5.2 GHz, the signal
level of port 1 is 8 dBi and its main lobe radiates in
the 17° direction, the main lobe of port 2 radiates in
the 21° direction and the signal level is 8.8 dBi.
Figure 11 (Appendix) shows the directivity and
gain values of the T microstrip antenna. Directivity
values for 2.4 GHz are 8.5 dBi in port 1 and 8.1 dBi
in port 2; for 5.2 GHz, it is 7.9 dBi in port 1 and 8.8
dBi in port 2. When the gain results are examined,
for 2.4 GHz, 6.9 dB in port 1 and 6.9 dB in port 2;
for 5.2 GHz, port 1 is 6.8 dB and port 2 is 7.8 dB.
When compared to the literature, it is understood that
the gain and directivity values give very good results
for microstrip antennas.
6 Conclusions
In this study, MIMO microstrip dual-band antennas
were designed using the CST simulation program,
and all designed antennas and AMC reflector
structures were produced with a printed circuit.
Antenna design and simulation with AMC substrate
formed the basis of this study. When the designed
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antennas are compared with literature values; they
have high gain (6.5-7 dB per antenna) and good
isolation (values above -20 dB per antenna).
Compared to existing classical dual-band MIMO
microstrip antennas; by using AMC substrates, an
antenna system with higher performance, higher
directionality and improved parameters has been
obtained. Achieving the desired insulation values
was made possible by the position of the antenna
elements relative to each other. The proposed designs
can be easily integrated into existing
WLAN/WIMAX receivers by simply changing the
antenna. Thus, it provides great flexibility for a wide
range of applications.
Target specifications and international standards
(WHO, FCC, etc.) are met with the designed
antennas. Multiple input multiple output technology
is a technology that enables increased
communication performance by using more than one
antenna in both the receiver and transmitter. MIMO
technology has attracted great attention because it
increases transmission speed and quality without
requiring more power or bandwidth. This;
increasingly high efficiency is achieved by line
application and reduced damping. Because of these
features, MIMO is the most important topic of
current wireless communication research.
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Contribution of individual authors to the creation
of a scientific article (ghostwriting policy)
The authors contributed in the present research, at all
stages from the formulation of the problem to the
final findings and solution.
Sources of Funding for Research Presented in a
Scientific Article or Scientific Article Itself
No funding was received for conducting this study.
Conflicts of Interest
The author(s) declare no potential conflicts of
interest concerning the research, authorship, or
publication of this article.
Creative Commons Attribution License 4.0
(Attribution 4.0 International, CC BY 4.0)
This article is published under the terms of the
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APPENDIX
Port 1
Port 2
Fig. 9: Far-field pattern results of T microstrip antenna for 2.45 GHz
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Port1
Port 2
Fig. 10: Far-field pattern results of T microstrip antenna for 5.2 GHz
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Port 1
Port 2
f=2.45 GHz
f=2, 4 GHz
f=5.2 GHz
Fig. 11: T microstrip antenna directivity and ga
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