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International Journal of Wireless & Mobile Networks (IJWMN) Vol. 3, No. 1, February 2011
DOI : 10.5121/ijwmn.2011.3106 62
E
NHANCED
G
AIN AND
B
ANDWIDTH OF
P
ATCH
A
NTENNA
U
SING
EBG
S
UBSTRATES
Mst. Nargis Aktar
1
, Muhammad Shahin Uddin
2
, Md. Ruhul Amin
3
, and
Md. Mortuza Ali
4
1
Department of Information and Communication Technology
Mawlana Bhashani Science and Technology University, Bangladesh
2
Department of Electronics, Kookmin University, Seoul, South Korea
3
Department of Electrical and Electronic Engineering
Islamic University of Technology, Dhaka, Bangladesh
4
Department of Electrical and Electronic Engineering
Rajshahi University of Engineering and Technology, Bangladesh
E-mail: {nargismbstu@gmail.com,
shahin.mbstu@gmail.com,
aminr_bd@yahoo.com,and mmali.ruet@gmail.com}
A
BSTRACT
Microstrip patch antenna becomes very popular day by day because of its ease of analysis and
fabrication, low cost, light weight, easy to feed and their attractive radiation characteristics. Although
patch antenna has numerous advantages, it has also some drawbacks such as restricted bandwidth, low
gain and a potential decrease in radiation pattern. In recent years, attention to use Electromagnetic Band
Gap (EBG) substrates to overcome the limitations of patch antenna. In this paper, we propose a
rectangular microstrip patch antenna with EBG substrates and compare the performance of the proposed
antenna with a conventional patch antenna in the same physical dimension. Due to the presence of the
EBG structure in the dielectric substrates, the electromagnetic band gap is created that reduces the
surface waves considerably. As a result, the performance of the proposed antenna is better comparing the
conventional existing microstrip patch antenna.
K
EYWORDS
Microstrip patch antenna, Electromagnetic band gap (EBG) substrates, Gain and Bandwidth.
1.
I
NTRODUCTION
With the drastic demand of wireless communication system and their miniaturization, antenna
design becomes more challenging. Recently microstrip patch antennas have been widely used in
satellite communications, aerospace, radars, biomedical applications and reflector feeds because
of its inherent characteristics such as light weight, low profile, low cost, mechanically robust,
compatibility with integrated circuits and very versatile in terms of resonant frequency,
polarization, pattern and impedance . In spite of its several advantages, they suffer from
drawbacks such as narrow bandwidth, low gain and excitation of surface waves, etc [1-3]. These
drawbacks limit their applications in other fields. In order to overcome the limitations of
microstrip patch antennas such as narrow bandwidth and low gain, numerous techniques are
proposed i.e. for probe fed stacked antenna, microstrip patch antennas on electrically thick
substrate, slotted patch antenna and stacked shorted patches have been proposed and
investigated [4-5]. These methods have eliminated the bandwidth problem for most applications.
But limitations
of gain and surface wave excitation still remain. That is why, in recent years
there has been considerable effort in the EBG structure for antenna application to suppress the
surface wave and overcome the limitations of the antenna. Many works have been done to
International Journal of Wireless & Mobile Networks (IJWMN) Vol. 3, No. 1, February 2011
63
improve the performance of the microstrip antennas [6-11]. The EBG structure utilizes the
inherent properties of dielectric materials to enhance the microstrip antenna performance. EBG
materials are periodic dielectrics that produce pass band and stop band characteristics.
In this paper, we propose a rectangular patch antenna with EBG substrates. The
characteristics of EBG depend on the shape, size, symmetry and the material used in their
construction. Surface waves are reduced by using EBG substrate which leads to increase the
directivity, bandwidth and radiation efficiency [15]. EBG were realized to reduce and eliminate
surface waves, which leads to an increase in directivity, bandwidth and radiation efficiency. It is
also useful to reduce the side lobes of the radiation pattern and hence radiation pattern front-to-
back ratio and overall antenna efficiency are improved. Our proposed antenna gives better
performance compare to the conventional rectangular microstrip patch antenna. A substantial
gain and bandwidth enhancement has been obtained. The design and simulation have been done
by using High Frequency Structure Simulator (HFSS). The remainder of the paper is organized
as follows: In section II, a brief description of EBG structure. In section III present the
conventional and proposed antenna design and configuration. In section IV present the
simulation results and discussion. The conclusion of this paper is provided in section V.
2.
E
LECTROMAGNETIC
B
AND
G
AP
S
UBSTRATES
The birth of the electromagnetic band gap structure has triggered many novel antenna
applications. Electromagnetic band gap structures can be defined as artificial periodic (or
sometimes non-periodic) objects that prevent or assist the propagation of electromagnetic waves
in a specified band of frequency for all incident angle and polarization state. Two commonly
employed features are suppressing unwanted substrate modes and acting as an artificial
magnetic ground plane. The main advantage of EBG structure is their ability to suppress the
surface wave current. The generation of surface waves degrades the antenna efficiency and
radiation pattern. Furthermore, it increases the mutual coupling of the antenna array which
causes the blind angle of a scanning array [12-14].
EBG structures are usually realized by periodic arrangement of dielectric materials and metallic
conductors. In general, they can be categorized into three groups according to their geometric
configuration; (i) three-dimensional volumetric structures, (ii) two-dimensional planar surfaces,
and (iii) one-dimensional transmission lines [13]. Two-dimensional planar EBG surfaces again
classified into two categories, first one is mushroom like EBG surfaces and another one is
uniplanar EBG surfaces.
For the mushroom like EBG surfaces, a band gap is observed between the frequency 7GHz and
11GHz. On the other hand, for the uniplanar EBG surfaces a band gap is observed the frequency
from 13GHz to 14.6GHz. In this paper, mushroom like EBG surface is used in order to design
patch antenna on EBG substrates because the mushroom like EBG surface has a lower
frequency band gap and a wider bandwidth than the uniplanar EBG surface.
A two dimensional mushroom like EBG structure is shown in Figure 1. Design of patch antenna
mushroom like EBG structures are preferable because light weight, low fabrication cost. There
are four main parameters affecting the performance of mushroom like EBG structures. The
parameters are like this: rectangle width w, gap width g, substrates thickness h and substrates
permittivity ε
r
. Also, the vertical vias radius r has a trival effect because it is very thin compared
to the operating wavelength. The parameters that are affecting the performance of EBG
structures are directly dependent on the operating wavelength of the patch antenna [8]. The
parameters are varying with operating wavelength as like this that the rectangle width, w varies
from 0.04λ
12 GHz
to 0.20λ
12 GHz
, gap width varies from 0.01λ
12 GHz
to 0.12λ
12 GHz
and the
substrate thickness, h varies from 0.01λ
12 G Hz
to 0.09λ
12 GH z
. Here, λ
12
means the wavelength
between medium 1 and 2 i.e. the free space and the guiding device and GHz means the
wavelength respect to the GHz range frequency.
International Journal of Wireless & Mobile Networks (IJWMN) Vol. 3, No. 1, February 2011
64
Figure 1 Two dimensional mushrooms like EBG surfaces: (a) Top view (b) Cross view
3.
A
NTENNA
D
ESIGN AND
C
ONFIGURATION
In order to identify and verify the improvement of the performance of microstrip antenna on
EBG substrates, designed a conventional antenna and the proposed antenna. The width of the
rectangular patch antenna is usually chosen to be larger than the length of the patch, L to get
higher bandwidth. The antenna is designed to operate at frequency 10GHz. In this paper, we use
neltec dielectric material as patch substrates whose dielectric constant is 2.45. The antenna is
excited by a microstrip transmission line feed. The point of excitation is adjustable to control the
impedance match between feed and antenna, polarization, mode of operation and excitation
frequency. To design patch antenna lower dielectric constant is used because in case of lower
dielectric constant of the substrates, surface wave losses are more severe and dielectric and
conductor losses are less severe. By using EBG structures, surface wave loss can be reduced
easily. Table1 shows the important parameters for the geometrical configuration of the patch
antenna.
Table1 Geometrical configuration of the patch antenna
Antenna Part Parameter Value
Patch
Length 8.8mm
Width 11.4mm
Patch Substrates
(NeltecN×9245)
(IM)(tm)
Dielectric constant 2.45
Height 0.787mm
Dielectric loss tangent 0.01
EBG Substrates
Rectangle Width 0.10λ
12 GHz
Gap Width 0.02λ
12 GHz
Substrates thickness 0.04λ
12 GHz
Operating Frequency 10GHz
Gap Width
Rectangle
Width
(a) Top view
(b) Cross view
International Journal of Wireless & Mobile Networks (IJWMN) Vol. 3, No. 1, February 2011
65
4.
SIMULATION
RESULTS
AND
DISCUSSIONS
Now a days, it is a common practice to evaluate the system performances through computer
simulation before the real time implementation. A simulator “Ansoft HFSS” based on finite-
element method (FEM) has been used to calculate return loss, impedance bandwidth, radiation
pattern and gains. This simulator also helps to reduce the fabrication cost because only the
antenna with the best performance would be fabricated. Figure 2 shows the simulated results of
the return loss of the conventional antenna and the proposed antenna.
Figure 2 Return losses of the conventional patch antenna and antenna with EBG
It is seen from the Figure 2, the return loss for the conventional patch antenna is – 14.5dB at
9.79GHz and for the proposed patch antenna is -23dB at 10.12GHz. A negative value for return
loss shows that this antenna had not many losses while transmitting the signals. According to
theoretical design, the minimum loss has been observed at 10 GHz. But from simulation results
we have observed that the minimum loss get at 9.79 GHz for conventional antenna and
10.12GHz for the proposed antenna. Thus the return loss of the proposed microstrip patch
antenna is 58.6% less compared to the conventional microstrip patch antenna. From the same
Figure 2, the antenna bandwidth can be calculated. At the point of return loss -10dB, the
bandwidth (BW) and the relative bandwidth (RBW) are 240MHz and 5.43% for conventional
patch antenna but at same point of return loss the bandwidth (BW) and the relative bandwidth
(RBW) of the proposed antenna are 330MHz and 7.33%. Therefore, the bandwidth of the
proposed antenna is 37.5% more than the conventional antenna.
The simulated results for gain that are obtained from conventional antenna and the proposed
antenna on EBG substrates are shown in Figure 3 and Figure 4.
8 8.5 9 9.5 10 10.5 11 11.5 12
-25
-20
-15
-10
-5
0
Frequency in GHz
Return Loss in dB
Conventional Antenna
Antenna with EBG
International Journal of Wireless & Mobile Networks (IJWMN) Vol. 3, No. 1, February 2011
66
Figure 3 Gain of the conventional rectangular patch antenna.
Figure 4 Gain of the rectangular patch antenna with EBG
From the simulated results, it is shown that the gain of the conventional antenna and the
proposed antenna is 22.3dB and 25.7dB. So, the gain of the proposed patch antenna on EBG
substrates is 15.2% more than the conventional patch antenna.
International Journal of Wireless & Mobile Networks (IJWMN) Vol. 3, No. 1, February 2011
67
The Figure 5 and Figure 6 shows the simulated directivity of the conventional antenna and the
proposed antenna.
Figure 5 Directivity of the conventional rectangular patch antenna.
From the Figure 5 and Figure 6, the directivity for the conventional patch antenna and the
proposed patch antenna are 23.4dBi and 25.5dBi. Thus, the directivity of the proposed antenna
is also enhanced of 8.97% than the conventional antenna.
Figure 6 Directivity of the rectangular patch antenna with EBG
International Journal of Wireless & Mobile Networks (IJWMN) Vol. 3, No. 1, February 2011
68
5.
C
ONCLUSION
The patch antenna mostly used in modern mobile communication. The goals of this paper are to
design conventional patch antenna and the patch antenna on EBG substrates with same physical
dimensions that can operate at 10GHz and study the performance of misrostrip antenna when
EBG structure added on it. From the simulated results, it is seen that the performance is better of
a patch antenna that is designed on EBG substrates than the conventional patch antenna. In
future, our targets are to real time implementation of the proposed antenna and also design
another microstrip patch antenna with EBG substrates that can operate at higher frequency.
References
[1]
Jing Liang
,
and Hung-Yu David Yang
,
“Radiation Characteristics of a Microstrip Patch over an
Electromagnetic Bandgap Surface,”
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[2]
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K.L. Wong
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International Journal of Wireless & Mobile Networks (IJWMN) Vol. 3, No. 1, February 2011
69
Authors
Mst. Nargis Aktar
received B.Sc. and M.Sc. in Electrical and Electronic
Engineering from Rajshahi University of Engineering and Technology
(RUET), Bangladesh in 2007 and 2010 respectively. She joined as a faculty
member in Electrical and Electronic Engineering department of Ahsanullah
University of Science & Technology (AUST), Bangladesh, in 2007. In 2008
she joined as a faculty member in the department of Information and
Communication Technology (ICT) of Mawlana Bhashani Science and
Technology University (MBSTU), Bangladesh. Her current research interests focus on Antenna
designing, optical communication, photonics.
Muhammad Shahin Uddin
received B.Sc. in Electrical and Electronic
Engineering from Rajshahi University of Engineering and Technology
(RUET), Bangladesh. Then, he joined as a faculty member in American
International University Bangladesh (AIUB) and Chittagong University of
Engineering and Technology (CUET), Bangladesh in 2005. In 2006 he joined
as a faculty member in the department of ICT of Mawlana Bhashani Science
and Technology University (MBSTU), Bangladesh. Currently he is continuing
his Masters studies in the department of Electronics Engineering of Kookmin University, Korea.
His current research interests are Visible Light Communication, RFID, LED-ID, Sensor
Network Smart Antenna Design and Wireless Cellular Networks.
Dr. Md. Ruhul Amin
is working as a Professor in Electrical and Electronic
Engineering at the Islamic University of Technology, a subsidiary organ of
OIC. He earned a Ph. D. in EEE from Niigata University, Japan, M. Sc.
Engineering from Bangladesh University of Engineering and Technology and
B. Sc Engineering from the University of Rajshahi. His research interests
include generation and application of High Power Microwaves, Antenna
theory and Signal Processing. He was the recipient of the Sir Thomas Ward
memorial medal awarded by the Institution of Engineers India. Professor
Amin has published 66 journal and conference papers so far. He served as the Dean of the
Faculty of Electrical and Computer Engineering at Rajshahi University of Engineering and
Technology. Professor Amin is a Commonwealth Fellow and a Fellow of the Institution of
Engineers, Bangladesh and a member of IEEE.
Dr. Md. Mortuza Ali
was born in Bangladesh in 1957. He received the B. Sc.
Engineering degree in Electrical and Electronic Engineering from Rajshahi
University, Bangladesh in 1982, and the M. Sc. and Ph. D. degrees from
Niigata University, Japan in 1989 and 1992, respectively. Since 2002 he has
been employed by Rajshahi University of Engineering & Technology,
Bangladesh as Professor in the Department of Electrical and Electronic
Engineering. His research interests include the high power microwave
devices, antennas and wave propagation, and numerical analyses of various
systems of linear/nonlinear equations.