IRJET- Design & Analysis of MIMO Microstrip Antenna with Improved Mutual Coupling

INTERNATIONAL RESEARCH JOURNAL OF ENGINEERING AND TECHNOLOGY (IRJET) E-ISSN: 2395-0056
VOLUME: 06 ISSUE: 08 | AUG 2019 WWW.IRJET.NET P-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.34 | ISO 9001:2008 Certified Journal | Page 1372
Design & Analysis of MIMO Microstrip Antenna with Improved Mutual
Coupling
Preeti Kumbhar1, Dr. D.S. Bormane2, Dr. D.G. Bhalke3
2Principal, AISSMS COE, Maharashtra, India
3HOD Dept. of E&TC Engineering, AISSMS COE, Maharashtra, India
------------------------------------------------------------------------***-------------------------------------------------------------------------
Abstract—: This work presents a defected ground structure
(DGS) for a dual component multiple input multiple output
(MIMO) antenna with improved mutual coupling. Defected
ground structure is accepted as an arising approach for
enhancing the different parameters of microwave circuits,
which are narrow bandwidth, low gain and isolation. The
two-element MIMO antenna operates at 3.3 GHz. The
designed mimo antenna has a compress size of 26 mm × 40
mm suitable for practical design of an antenna. The antenna
can be applicable for WLAN, Wi-Max, Wi-Fi which covers a
patch operating at a frequency range 2.7 GHz to 5.1GHz. The
antenna attains peak gain of 1.17 dB. Efficiency of the
antenna is 94%.
Keywords — MIMO, Defected Ground Structure, Isolation.
1. Introduction
MIMO (multiple input multiple output) is
an antenna technology for wireless communications in
which multiple antennas are used at both the origin
(transmitter) and the target (receiver). The antennas at
both end of the broadcasting circuit are combined to
reduce errors and optimize data speed. MIMO technology
uses Multipath to boost wireless performance. MIMO
technology takes a single data stream and breaks it down
into some discrete data streams and sends it out over
multiple antennas. MIMO becomes an essential segment of
wireless communication excellence which involves
WLAN/WPAN, WiFi, WiPro and WiMAX.
The antenna consists of two planar monopoles. Planar
monopoles are placed such as to obtain good isolation.
Two long ground stubs and short ground strip are exerted
to enhance the isolation [1]. Two novel bend slit on ground
behind antenna element is used for the reduction in
mutual coupling. The slits are tilts by 90º, to reduce the
effect of slits on impedance bandwidth [2]. Dumbbell
shaped structure is used for the reduction in mutual
coupling [3]. A dual slot patch along with parasitic
elements is used for isolation enhancement. For the
improvement in isolation, two elements are responsible
which are parasitic monopole element and symmetric slot
element [4]. Novel miniaturized two layer Electromagnetic
Band Gap structure is introduced For the reduction in
electromagnetic coupling. There is reduction in mutual
coupling by using EBG structure [5]. To enhance the
isolation and for the design and implementation of antenna
modified serpentine structure is used. Modified serpentine
structure acts like a band-reject filter, so that the mutual
coupling of the antenna is reduced [6]. There is another
technique for mutual coupling reduction that is by using
metamaterials. This technique attained a -14 dB reduction
in mutual coupling at 2.45 GHz and -13 dB at 5.2 GHz [7].
The technique slotted meander-line resonator (SMLR) is
used to enhance the isolation in microstrip patch antenna
arrays. This structure particularly designed for band-notch
function. The proposed design provides an improvement
in isolation by -16 dB [8]. Planar electromagnetic band gap
(EBG) structure based on a truncated frequency selective
surface is used. The reduction in the number of elements
and isolation has been examined. By using this technique
mutual coupling is reduced by more than -10 dB [9].
Photonic band-gap (PBG) structure is a new structure
introduced to improve the isolation of antennas array. The
presented technique is using spurline structure in the
ground plane between antennas array which effectively
suppresses mutual coupling [10].
Here in this paper we are designing a multiple input
multiple output (MIMO) microstrip antenna with improved
mutual coupling. For the reduction of mutual coupling
there are various techniques like Decoupling Networks,
Parasitic Elements, Neutralization Lines and
Metamaterials. In this paper our aim is to reduce mutual
coupling and improve the isolation. For this purpose we
are using defected ground ease of use structure technique.
The compact geometrical slots embedded on the
ground plane of microwave circuits are referred to
as Defected Ground Structure (DGS). A single defect (unit
cell) or multiple periodic and aperiodic defects
configurations may be comprised in DGS. In wireless
communication system there is high demand for high data
rates and channel bandwidth. It is very necessary in
modern wireless system to shift towards multiple input
multiple output from single input single output and single
input multiple output. MIMO antenna is interesting and
attractive topic as it has so many challenges to achieve.
Some of the challenges are to improve channel capacity,
bandwidth, gain, polarization diversity and reduce
coupling between inter elements. As these are the multiple
input multiple output antennas i.e. multiple element
antennas there is high demand for size minimization so
that they can fit in the compact and robust equipment.
1Student, Dept. of E&TC Engineering, AISSMS COE, Maharashtra, India

2. Methodology
2.1. Methods
For the design of the antenna we have used Ansoft HFSS
software. HFSS stands for high-frequency structure
simulator. It is one of several commercial tools used
for antenna design, and the design of filters, transmission
lines, and packaging.
The designed antenna is fabricated on FR-4 substrate
having thickness of 1.6 mm and is fed by 50 Ω microstrip
line on ground plane. There are some formulae that should
be used while designing an antenna.
2.2. Formulae used
Width of Patch ( )-
The width of the Microstrip patch antenna is calculated as
(1)
where,
c = (3 x m /s)
𝑓 = operating frequency
ℰᵣ = dielectric permittivity of 4.4
Effective dielectric const ( )-
Fringing E-fields on the edge of the microstrip antenna add
up in phase and produce the radiation of the
microstrip antenna. An effective dielectric constant is
introduced, since some of the waves travel in the substrate
and some in air, and is given as:
=
ℰ ℰ
√ (2)
= effective dielectric
h = thickness of the dielectric substrate
The effective length because of fringing is given as:
=
√
(3)
Since the fringing is there the dimension of the patch as
increased by on both the sides, given by:
(4)
Feed Length-
Feed length (𝑓𝑙) = (5)
λ = wavelength of antenna
Feed width-
Ζ =
√
(6)
Where,
w = width of feed line
t = thickness of dielectric constant
Z = 50ohm
Here a MIMO antenna using microstrip line feeding is
constructed by placing two single antennas side by side at
distance of 26 mm from feeding point to feeding point. The
total size of antenna is 40 mm x 26 mm x 1.6 mm. The
structure of the projected MIMO antenna is demonstrated
in figure1. It is made up of two patches in rectangular
shape with dimension of 10mm x 10mm. The Microstrip
feed line extended from patch to feed point. The Defected
Ground Structure is preferred to get better isolation. There
are different shapes of DGS available like rectangular,
circular, dumbbell etc. but the best results are obtained
from stub DGS. Stubs are introduced on ground plane and
the thickness of two stubs is 1 mm each. The dimensions of
design shown in figure 2 are in millimeter. The FR4
dielectric material is used as a substrate as it is available
easily. The thickness of substrate is 1.6 mm with dielectric
constant 4.4.
Fig. 1: Structure of MIMO antenna
2.3. Simulation Result
The antenna is simulated using HFSS (High Frequency
Structure Simulator). The structure of the proposed
antenna is displayed in fig.1.

Fig 2: Simulated reflection coefficient characteristics of an
antenna
The simulated reflection coefficient characteristics of an
antenna have been depicted in Fig. 2.The characteristics
shown in Fig.2 indicate that the antenna radiates at 3.38
GHz. The frequency band observed between 2.7 GHz to 5.1
GHz.
Fig 3: Isolation characteristics S12 of an antenna
The reflection coefficient (S11 & S22) observed at
resonance 3.29 GHz is -32.73 dB and with isolation of -
29.09 as shown in Fig.3.
Fig 4: 3D Gain of the antenna
With this configuration the gain of antenna is found to be
1.17 dBi with directivity of 1.24 dBi. The directivity of an
antenna is shown in Fig.5. The 2D radiation pattern of the
antenna is shown in the Fig.6.
Fig 5: 3D Directivity of the antenna
Fig 6: 2D Radiation Pattern
2.4. Measured Results
Measured Results of the proposed mimo antenna with
defected ground structure have been depicted in Fig. 7 (a)
and (b). Measured reflection coefficient characteristics i.e.
S11 shown in Fig. 7(a) which is 3.39 GHz similar to the
simulated result in HFSS.
Fig 7(a): Measured reflection coefficient characteristics

Fig. 7(b) shows S12 parameter i.e. isolation characteristic
of an antenna. It is the effectively seen that the mutual
coupling between antenna elements is below -25 dB and -
20 dB respectively.
Fig 7(b): Measured isolation characteristics S12 of an
antenna
There is a little dissimilarity in simulated and measured
results. This difference may be due to the change in
permittivity of substrate material between simulated and
actual value or due to the losses in connector, cable and
soldering.
3. Conclusion
A MIMO antenna is proposed for Wi-MAX, WiFi and WLAN
application. It covers the frequency band of 2.7 GHz to 5.2
GHz which is useful Wi-MAX /WLAN applications. The
reflection coefficient of antenna is observed below -10dB
at respective resonant frequencies which is -32.73 while
the transmission coefficient is found -29.09 dB which
indicated better isolation. The maximum gain of achieved
by an MIMO antenna is 1.17 dBi and the antenna achieved
excellent efficiency up to 94 %.
References
[1] Qian Li, Member IEEE, Alexandros P. Feresidis,
Senior Member IEEE, Marina Mavridou and Peter
S. Hall, “Miniaturized Double-layer EBG Structures
for Broadband Mutual Coupling Reduction
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Raviteja, and M. G.Nabi, “Deployment of Modified
Serpentine Structure for Mutual Coupling
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IEEE Trans. Antennas Propagation, volume 56, no.
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[6] P. Hsieh, T. Chiu , K. Huang, and Wu H. B.,
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[7] Zhengyi Li, Zhengwei Du, & Ke Gong “A Dual slot
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[8] Jian-Feng Li, Qing-Xin Chu, and Tian-GuiHuang, “A
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[9] Muhammad U. Khan, Mohammad S. Sharawi,
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IEEE, 2013.
[10] Li Liu, S. Cheung and T. Yuk, “Compact MIMO
Antenna for Portable Devices in UWB
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propagation, Vol. 61, No. 8, August 2013.

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