Novel Design of Superimposed Square Slot Microstrip Array Antenna for Wide Bandwidth and High Gain

International Journal of Advanced Research in Engineering and Technology (IJARET),
ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 1, January (2014), © IAEME
187
A NOVEL DESIGN AND DEVELOPMENT OF SUPERIMPOSED SQUARE
SLOT TWO ELEMENT RECTANGULAR MICROSTRIP ARRAY ANTENNA
FOR WIDE BANDWIDTH AND INTENSIFIED GAIN
Dr. Nagraj Kulkarni1
and Dr. S. N. Mulgi2
1
Department of Electronics, Government College, Gulbarga-585 105, Karnataka, India
2
Department of PG Studies and Research in Applied Electronics, Gulbarga University,
Gulbarga-585106, Karnataka, India
ABSTRACT
A novel design of two element rectangular microstrip array antenna incorporating the two
superimposed square slots on the radiating patches is presented for wide bandwidth and high gain.
The maximum bandwidth of 93.07 % with a peak gain of 9.24 dB is achieved in the present study.
The antenna exhibits a virtual size reduction of 27% and shows broadside radiation pattern across its
entire operating band. The design concept of the antenna is described. The experimental results are
presented and discussed. The proposed antenna may find applications in WiMax of IEEE802.16d
(5.7-5.9 GHz), HIPERLAN/2 (5.725 to 5.825 GHz) and radar communication systems.
Key Words: Two element, superimposed, square slot, wideband, high gain
1. INTRODUCTION
In recent years, microstrip antennas (MSAs) have become the attractive candidate for the
antenna designers because of their useful features such as low profile, light weight compatibility
with integrated-circuit technology [1] etc. The patch antennas are receiving increasing interest in
various newly emerging communication systems such as WLAN, WiMAX, HIPERLAN/2 etc, since
they provide many advantages over traditional microwave antennas in terms of achieving dual, triple
and multiple bands which are realized by using different techniques such as, cutting slots of different
geometries like rectangular, L-shape, E-shape, circular, square [2-7] etc. In many applications, the
wide bandwidth and gain are the essential components to use the antenna for specific applications.
During the last decade, many efforts have been put forth to realize bandwidth widening techniques of
microstrip antennas, which include the use of impedance matching, multiple resonators and a thick
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188
substrate [8, 9] etc. But, the two element array antenna having a superimposed square slot on the
rectangular radiating patch and H shaped slots on the ground plane is used for enhancing the
bandwidth and gain. This kind of study is found to be rare in the literature. The slot loading
technique provides the freedom to design the required slot irrespective of their size or shape and can
be suitably loaded at the desired place on the geometry of the antenna for broadening the bandwidth
of the antenna [10]. Also, the array technique, gives the flexibility to design the required feed line
between the array elements to energize, which helps in enhancing the gain of the antenna [11].
2. ANTENNA DESIGN
The low-cost glass epoxy substrate material of area ASub × BSub having a thickness of h = 1.6
mm and dielectric constant εr = 4.2 is used to fabricate the proposed antenna. Artwork of the
antennas is sketched using computer software Auto-CAD to achieve better accuracy. The antennas
are etched using photolithography process.
Fig. 1: Geometry of SSTRMSAA
Figure 1 shows the geometry of the superimposed square slot loaded two element rectangular
microstrip array antenna (SSTRMSAA). The antenna has two rectangular patches that are present at
distance of D1 mm possessing the length L and width W that are designed for the resonant
frequency of 3.5 GHz, using the basic equations,
(1)
where, c is the velocity of light in mm, fr is the designed frequency in GHz,
εe is the effective dielectric constant and ∆l is the extension length of the fringing field in mm.
r e
c
L = 2 l (mm)
2f ε
− ∆

189
The ∆l and εe are given by,
(2)
The square slot of sides X mm is considered as base slot whose dimensions are constant
while another variable square slot of sides Y mm is superimposed on the base slot. These square slots
are placed at the center of the rectangular patch at a distance of 6.2 mm and 9.3 mm from non
radiating side (L) and the radiating side (W) of the patch. The two H shaped slots which are D2 mm
apart and each having a width 1 mm are incorporated on the ground plane such that the mid-point of
H slot lies exactly below the center of the each radiating patch. The HH and HV are the horizontal and
vertical arm lengths of the H shaped slot. The dimensions D1, D2, X, HH and HV are taken in terms of
λ0, where λ0 is the free space wavelength in millimeter corresponding to the designed frequency of
3.5 GHz. The parallel feed arrangement is used in the present study, because it has the advantage
over series fed arrangement, that is, its wideband performance. The feed arrangement shown in this
figure is a contact feed and has the advantage that it can be etched simultaneously along with the
antenna elements. The microstripline feed arrangement is designed using the relations available in
the literature [12]. A 50 feed line of length L50 and width W50 is connected to 100 line of length
L100 and width W100 to form a two way power divider. A quarter wave transformer of length LTr and
width WTr is connected between 100 feed line and midpoint of the radiating elements to establish
perfect impedance matching. A 50 semi miniature –A connector is used at the tip of the 50 feed
line. The various parameters of the proposed antenna are enlisted in Table 1.
Table 1: Various parameters of SSTRMSAA
Antenna
Parameters
Dimensions
in (mm)
Antenna
Parameters
Dimensions
in (mm)
W 26.6 WTr 0.15
L 20.4 X 4
L50 21.84 D1=D2 λ0/1.96
W50 3.2 ASub 90
L100 21.88 BSub 50
W100 0.74 HV λ0/9.96
LTr 10.92 HH λ0/8.32
( )
( )
e
e
W
ε + 0.3 +0.264
h
l = 0.412h
W
ε 0.258 +0.8
h
  
  
  ∆
  −   
  
1
-
2
r r
e
ε +1 ε 1 h
ε = + 1+12
2 2 W
−  
 
 
r r
c 2
W =
2f ε +1

190
3. RESULTS AND DISCUSSION
The Vector Network Analyzer (Germany make, Rohde and Schwarz, ZVK model 1127.8651)
is used to measure experimental return loss of SSTRMSAA. The experimental impedance bandwidth
over return loss less than -10 dB is calculated using the formula,
2 1
Bandwidth (%) =
C
f f
f
−
× 100 %
where, f2 and f1 are the upper and lower cut off frequencies of the resonating bands
when their return loss reaches -10 dB and fC is a centre frequency of f2 and f1.
Fig. 2: Variation of return loss versus frequency of SSTRMSAA when X= 4 mm and Y=2 mm
Figure 2 shows the return loss versus frequency of SSTRMSAA when X= 4 mm and Y=2
mm. It is clear from this figure that, the antenna resonates for dual bands with their respective
bandwidths are BW1=17.6 % (6.74-5.65 GHz) and BW2= 11.27% (8.43-7.53 GHz). The resonating
bands BW1 and BW2 are due to the fundamental resonance of the patches and the currents along the
edges of the superimposed square slots.
Fig. 3: Variation of return loss versus frequency of SSTRMSAA when X= 4 mm and Y=4 mm.

191
Figure 3 shows variation of return loss versus frequency of SSTRMSAA when the side length
of the superimposed square slot is increased from 2 mm to 4 mm. It can be noted from this figure
that, the antenna resonates again for two bands with their respective bandwidths are BW3=48.52%
(6.76-4.12 GHz) and BW4= 60.79% (14.5-7.74 GHz). Further, it is observed from this figure that, the
bandwidths BW3 and BW4 are enhanced from 17.6% to 48.52% and 11.27 % to 60.79% respectively
when compared to the bands BW1 and BW2 of Fig. 2. This increase in the bandwidth is due to effect
of increase in the combined area of the two superimposed square slots. Also, the H shaped slot on the
ground plane helps in widening the bandwidth of the antenna.
Fig. 4: Variation of return loss versus frequency of SSTRMSAA when X= 4 mm and Y=3 mm
Figure 4 shows the return loss versus frequency of SSTRMSAA when the side length of the
superimposed square slot is decreased from 4 mm to 3 mm. It is clear from this figure that the
antenna resonates for three bands with their respective bandwidths are BW5= 20.7% (2.82-2.29 GHz)
BW6= 5% (3.28-3.12 GHz) and BW7= 93.07% (12-4.38 GHz). The combined effect of decrease in
the area of the superimposed square slots and the presence of H shaped slot on the ground plane
makes two bands BW3 and BW4 shown in Fig. 3 to split into three bands BW5, BW6 and BW7
causing the first band BW5 to resonate at 2.555 GHz, which is less than the designed frequency i.e.
3.5 GHz, this shows the virtual size reduction of about 27%. The second band BW6 resonates at 3.2
GHz which is very close to the designed frequency of antenna shows the fundamental resonance of
the antenna. Furthermore, the bandwidth of the third band BW7 is enhanced to a maximum of
93.07% when compared to the BW4 of Fig. 3. Hence it is clear that the variation of location of the
superimposed square slot on the patch element is effective in controlling the bandwidth of the
antenna.
Fig. 5: Radiation pattern of SSTRMSAA measured at 6.195 GHz.

192
Fig. 6: Radiation pattern of SSTRMSAA measured at 5.44 GHz
Fig.7: Radiation pattern of SSTRMSAA measured at 3.2 GHz
The co-polar and cross-polar radiation patterns of SSTRMSAA are measured in their
operating bands at 6.195, 5.44 and 3.2 GHz respectively and are as shown in Figures 5 to 7.
From these figures, it can be observed that, the patterns are broadside and linearly polarized,
the cross polar level is maximum -15 dB down when compared to their co–polar power level
indicates the directional nature of the radiation.
The gain of SSTRMSAA is calculated using the absolute gain method given by the relation,
0
( ) 10 log - ( ) - 20log
4
r
t
t
P
G dB G dB dB
P R
λ
π
=
   
  
  
(3)
where, Gt is the gain of the pyramidal horn antenna and R is the distance between the
transmitting antenna and the antenna under test (AUT). The power received by AUT, ‘Pr’ and the
power transmitted by standard pyramidal horn antenna ‘Pt’ are measured independently. The
SSTRMSAA gives a peak gain of about 9.24 dB in its operating band when X = 4 mm and Y = 2
mm. The variation of gain versus frequency of SSTRMSAA is plotted in Fig. 8.

193
Fig. 8. Variation of gain versus frequency of SSTRMSAA
4. CONCLUSION
From the detailed study, it is found that, the SSTRMSAA can be made to operate between
2.82 to 12.43 GHz by loading two superimposed square slots on the radiating patch and H shaped
slots on the ground plane. The bandwidth is enhanced to 93.07 % by varying the combined area of
superimposed square slots. The SSTRMSAA also gives a peak gain of 9.24 dB which is quite large
when compared to the gain of conventional rectangular microstrip antenna designed for the same
resonant frequency. The variation of the dimension of superimposed square slot on the patch does
not change the nature of broadside radiation characteristics. The proposed antennas are simple in
their geometry and are fabricated using low cost glass epoxy substrate material. These antennas may
find applications in WiMax of IEEE802.16d (5.7-5.9 GHz), HIPERLAN/2 (5.725 to 5.825 GHz) and
radar communication systems.
ACKNOWLEDGEMENTS
The authors would like to thank the Dept. of Science & Technology (DST), Govt. of India,
New Delhi, for sanctioning Vector Network Analyzer to this Department under FIST project.
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BIO-DATA
Dr. Nagraj Kulkarni
Electronics from Gulbarga Universit
respectively. He is working as a
Electronics Government Degree college Gulbarga.
of Microwave Electronics.
Dr. S.N. Mulgi received
from Gulbarga University Gulbar
is working as a professor in the Department of
University, Gulbarga.
Electronics.
6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 1, January (2014), © IAEME
194
Behera,. S, and Vinoy, K.J, “Microstrip square ring antenna for dual band operation,”
Progress In Electromagnetics Research, PIER 93, 41–56, 2009.
, M., Geran, F, and Dadashzadeh, G, “A compact microstrip square
antenna for UWB applications,” Progress In Electromagnetic Research PIER
Roy .J.S., Chattoraj, and N. Swain, “short circuited microstrip antenna for multi
Microwave and Optical Technology Letters, Vol .48, 2372
Rafi, Gh. Z, and Shafai, L, “Wideband V-slotted diamond-shaped microstrip patch
Electronics Letters, Vol. 40, No. 19, 1166-1167, 2004.
N. M. Sameena, R. B. Konda, and S. N. Mulgi, “Broadband, high-gain Complementary
symmetry Microstrip array antenna,” Microwave and Optical Technology Letters
Y.S. Kumar, V.V. Srinivasan, V.K. Lakshmeesha, and S. Pal, “High gain,
aperture coupled microstrip Antenna”, Proceedings of the
osium India (IRSI-07), 228–230, 2007.
Bahl, I. J, and P. Bhartia, Microstrip Antennas, Artech house, New Delhi, 1980
P. Naveen Kumar, S.K. Naveen Kumar and S.N.Mulgi, “Design and Development of
Rectangular Microstrip Antenna for Quad and Triple Band Operation”, International Journal
138, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472.
Shivasharanappa N Mulgi, “Complementary-Symmetric Corner Truncated
Compact Square Microstrip Antenna for Wide Band Operation”, International Journal of
Electronics and Communication Engineering & Technology (IJECET), Volume
, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472.
Shivasharanappa N Mulgi,, “Design and Development
Dual Band Microstrip Antenna with Enhanced Bandwidth, Gain, Frequency Ratio
ernational Journal of Electronics and Communication Engineering &
Technology (IJECET), Volume 1, Issue 1, 2010, pp. 88 - 98, ISSN Print: 0976
Nagraj Kulkarni received his M.Sc, M.Phil and Ph.D degree in Applied
Electronics from Gulbarga University Gulbarga in the year 1995,
respectively. He is working as an Assistant professor and Head in the Department of
Electronics Government Degree college Gulbarga. He is actively working
of Microwave Electronics.
received his M.Sc, M.Phil and Ph.D degree in Applied Electronics
from Gulbarga University Gulbarga in the year 1986, 1989 and 2004 respectively. He
professor in the Department of Applied Electronics Gulbarga
University, Gulbarga. He is an active researcher in the field of Microwave
6499(Online) Volume 5, Issue 1, January (2014), © IAEME
Behera,. S, and Vinoy, K.J, “Microstrip square ring antenna for dual band operation,”
, M., Geran, F, and Dadashzadeh, G, “A compact microstrip square-ring slot
Research PIER 67, 173-
antenna for multi-band
Vol .48, 2372-2375,
shaped microstrip patch
gain Complementary-
Microwave and Optical Technology Letters, Vol. 52,
Lakshmeesha, and S. Pal, “High gain, low side lobe,
the Inter -national
rtech house, New Delhi, 1980.
P. Naveen Kumar, S.K. Naveen Kumar and S.N.Mulgi, “Design and Development of
ernational Journal
Symmetric Corner Truncated
ernational Journal of
Electronics and Communication Engineering & Technology (IJECET), Volume 1, Issue 1,
nd Development of Low Profile,
ith Enhanced Bandwidth, Gain, Frequency Ratio and Low
ernational Journal of Electronics and Communication Engineering &
, ISSN Print: 0976- 6464,
degree in Applied
y Gulbarga in the year 1995,1996 and 2014
in the Department of
He is actively working in the field
his M.Sc, M.Phil and Ph.D degree in Applied Electronics
ga in the year 1986, 1989 and 2004 respectively. He
Applied Electronics Gulbarga
field of Microwave

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