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1. Srilakshmi.A, N.V.Koteswara Rao, D.Sreenivasa Rao / International Journal of Engineering Research
and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 4, June-July 2012, pp.943-946
Bandwidth Enhancement Using Figure Eight Shaped Slot Antenna
Srilakshmi.A
Associate professor, Vasavi college of Engineering, ECE department, Hyderabad, India
N.V.Koteswara Rao
Head and Professor of ECE, CBIT, Hyderabad, India
D.Sreenivasa Rao
Professor of ECE, JNTUH,Hyderabad , India
Abstract
An eight shaped annular ring slot antenna is of figure eight and a vertical reference line. The optimized
presented. A simple 50 ohms microstrip line is used to results are found to be impedance bandwidth more than
excite the slot. Two annular slots are linked to achieve 1GHz. A simple 50 ohms microstrip line is used to excite
wide band width. Parametric Design and Analysis is the slot.
carried out with permutations of the angle between the line Parametric Analysis is carried out with
joining the centers of the two rings of eight shaped slot and combinations of the angle between the line joining the
a vertical reference line and with permutations of the centers of the two rings of eight shaped slot and a vertical
distance between the centers of the two rings of eight reference line from 15 to 90 degrees in steps of 15 degrees
shaped slot. Its optimal impedance band width(S11<-10dB) and with permutations of the distance between the centers
is 2. to 3.5 GHz, more than 1GHz , 55% centered at of the two rings of eight shaped slot from 7 mm to 9.5 mm
2.7GHz. in steps of 0.5mm. The Antenna Size is 35mm x 65mm
x1.6mm. Its optimal impedance band width(S 11<-10dB) is
Keywords Microstrip Antenna, Wideband, Annular 2.12 to 3.16 GHz, more than 1GHz , 44% centered at
Ring Slot 2.3GHz at angle of rotation is 15 degrees and centre to
centre distance 17mm.. The simulated and measured
INTRODUCTION results are explained below.
It is well known that annular ring patch antennas
[1-5] and annular slot antennas[6-9] have bring interest CONFIGURATION AND DESIGN OF EIGHT
because of their significant characteristics such as wide SHAPED ANNULAR RING SLOT ANTENNA
bandwidth, small size, light weight and ease of fabrication. The configuration of figure eight shaped annular
Normally the bandwidth for single frequency annular slot ring slot antenna is illustrated in figure1. It consists of eight
is about 10%[6,9]. Several techniques have been reported shaped annular slot. The slot antenna is excited by a 50
to achieve broad band for annular slot antennas[9,10]. It ohms microstrip line to provide impedance matching.
has been reported in the subsequent work [11-14], annular Normally the resonant frequencies are mainly found by
slot antenna have 10-20% impedance bandwidth, which is circumference length of annular slot.
wider than conventional microstrip patch antenna. The annular- slot width and the microstrip feed line
However the development of wireless parameters have significant effect on antenna parameters.
communications experiencing an exponential growth hence The fundamental resonant frequency of
increase the need for wideband microstrip antennas. As a conventional annular circular ring slot antenna comprises
result, new antennas have to developed to provide larger in the ground plane of a dielectric substrate fed by a
bandwidth and this, within small dimensions. challenge microstrip conductor can be calculated according to the
which arises is that the gain and bandwidth performances following[12]
of an antenna are directly related to its dimensions. These 300
f0  ------------- 1
applications include WWANs, WLANs and WPANs. 2 Rm  re
Usually, broad band characteristics are tough to achieve, Where Rm is the average radius of inner ring radius and
because good impedance matching is difficult. outer ring radius in mm. f0 is the resonant frequency in
In this paper an 8- shaped slot antenna is
GHz. And  re is effective dielectric constant of annular
proposed, there by increasing the surface current path and
enabling wide bandwidth of the slot antenna. By adjusting ring patch is given by
2 r
the parameters of the antenna parametric analysis is carried  re  ------- 2
out using HFSS software by changing the inclination angle 1  r
that is angle between the line joining centers of two circles
943 | P a g e

2. Srilakshmi.A, N.V.Koteswara Rao, D.Sreenivasa Rao / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 4, June-July 2012, pp.943-946
To improve the impedance bandwidth one more annular RESULTS AND DISCUSSIONS
linked slot is introduced. Using below equation width of Based on the simulated results effect of angle of
the microstrip line width for 50 ohms is calculated[15]. rotation and center to center distance of two annular slots
87 5.98h of eight shaped slot are discussed in the following section.
Z0 ()  ln[ ] -----3
 r  1.41 (0.8w  t )
DEPENDENCE ON THE ANGLE OF
ANALYSIS AND STUDY OF THE ROTATION AND CENTER TO CENTER
PARAMETERS DISTANCE
The Return loss plots by adjusting the rotation
W angle AG and distance of separation between the centers
y of rings 2Rc are shown in Figure.2. It is observed in
figure.2 that impedance bandwidth for return loss below -
AG 10 dB is from 2.28 GHz to 3.64 GHz when angle of
rotation AG = 15 degrees and Rc =9mm, which is more
than 44 % centered at 2.3GHz. % Bandwidth for different
L combinations of antenna parameters is shown in figure 3.
Rc Ro and in table1. Flatten gain of 4dBi is observed over the
optimized band, shown in figure 4. It is also observed that
Ri E plane and H plane Radiation patterns at different values
of frequencies are relative omni directional shown in figure
5.
50 ohms
feed line SMA Ansoft Corporation XY Plot 1 HFSSModel4-WITH AG = 15
Connector -10.00
-12.00
Figure1. Geometry of the Eight shaped antenna
RETURN LOSS PLOT FOR AG = 15 degrees
-14.00
-16.00
-18.00
In this paper, the effects of eight shaped slot -20.00
antenna parameters are discussed and analyzed using HFSS -22.00 Curve Info
AG='15' fw ='3.5mm' h='1.6mm' l='35mm' Rc='7mm' Ri='6.
AG='15' fw ='3.5mm' h='1.6mm' l='35mm' Rc='7.5mm' Ri='
software which is a FEM based simulator.. Annular slot -24.00
AG='15' fw ='3.5mm' h='1.6mm' l='35mm' Rc='8mm' Ri='6.
AG='15' fw ='3.5mm' h='1.6mm' l='35mm' Rc='8.5mm' Ri='
-26.00
antennas have relatively broad band characteristics AG='15' fw ='3.5mm' h='1.6mm' l='35mm' Rc='9mm' Ri='6.
compare to conventional patch antennas. Normally , for Ansoft Corporation
2.00 2.50 3.00
XY Plot 5
Freq [GHz]
3.50
HFSSModel2
narrow slot antennas impedance bandwidth is around 10%. -10.00
However for wide slots high bandwidth can be obtained,
% Bandwidth
-12.00
because of reduced quality factor. -14.00
dB(S(LumpPort1,LumpPort1))
A single layer with 8 shaped slot is taken out of
infinite ground plane. FR4 substrate was selected to -16.00
reduce the cost, which has a relative permittivity of 4.4, -18.00 Curve Info
AG='30deg' h='1.6mm' l='35mm' Rc='7mm'
loss tangent of 0.01 and a thickness of 1.56 mm. The -20.00 AG='30deg' h='1.6mm' l='35mm' Rc='7.5m
ground plane size was 65mmX35mm. Radius of inner ring AG='30deg' h='1.6mm' l='35mm' Rc='8mm'
AG='30deg' h='1.6mm' l='35mm' Rc='8.5m
of the slot is Ri=6.5mm,Radius of the outer ring slot is -22.00
taken as Ro=9.5mm. Ansoft Corporation
2.50 3.00 3.50
XY Plot 5
Freq [GHz]
4.00 4.50
HFSSModel2
The 50 ohms feed line length is fl= 19.5mm, and -10.00
width is fw3mm was designed for good impedance
-15.00
matching. Radius of the inner slot ring is Ri=6.5 mm ,
radius of the outer circle of ring is Ro=9.5 mm, separation
dB(S(LumpPort1,LumpPort1))
-20.00
distance between the centers of two slots is 2Rc and the
angle between the line joining the centers of the two rings -25.00
Curve Info
of eight shaped slot and a vertical reference line is AG. The -30.00
AG='45deg' h='1.6mm' l='35mm' Rc='7mm'
dimensions Ri,, Ro, optimized to get wider bandwidth. AG='45deg' h='1.6mm' l='35mm' Rc='7.5m
AG='45deg' h='1.6mm' l='35mm' Rc='8mm'
Angle of inclination AG is varied from 15 to 90 -35.00
AG='45deg' h='1.6mm' l='35mm' Rc='8.5m
degrees insteps of 15degrees. The half of the distance 2.50 3.00 3.50 4.00 4.50
Freq [GHz]
between the centers of two linked annular rings is Rc is
varied from 7 to 9.5 mm insteps of 0.5mm. Only one
parameter is varied every time in the numerical simulation
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3. Srilakshmi.A, N.V.Koteswara Rao, D.Sreenivasa Rao / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Ansoft Corporation XY Plot 5 Vol. 2, Issue 4, June-July 2012, pp.943-946 HFSSModel2 Ansoft Corporation XY Plot 6 HFSSModel1
5.00
Curve Info
-10.00 dB(GainTotal)
Setup1 : Sw eep1
Phi='0deg'
dB(GainTotal)
Setup1 : Sw eep1
-12.00 Phi='90deg'
0.00
dB(S(LumpPort1,LumpPort1))
-14.00
dB(GainTotal)
-16.00 -5.00
Curve Info
-18.00 AG='60deg' h='1.6mm' l='35mm' Rc='7mm' Ro='9.5mm' w='65m
AG='60deg' h='1.6mm' l='35mm' Rc='7.5mm' Ro='9.5mm' w='65
-10.00
AG='60deg' h='1.6mm' l='35mm' Rc='8mm' Ro='9.5mm' w='65m
-20.00
AG='60deg' h='1.6mm' l='35mm' Rc='8.5mm' Ro='9.5mm' w='65
AG='60deg' h='1.6mm' l='35mm' Rc='9mm' Ro='9.5mm' w='65m
2.00 2.50 3.00 3.50 4.00 4.50
Ansoft Corporation Freq [GHz]
XY Plot 1 HFSSModel1
-15.00
-9.00 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00
Freq [GHz]
-11.00 Figure. 4 Gain performance of the antenna
-13.00
Return loss for 45 degrees angle
-15.00
Radiation Pattern 5
0 Curve Info
-17.00
Phi='0deg'
Curve Info
-30 30 Phi='90deg'
AG='75deg' b='50mm' fl='19.5mm' fw='3.5mm' h='1.6mm' l='35mm' Rc='7mm' 10.00
-19.00
AG='75deg' b='50mm' fl='19.5mm' fw='3.5mm' h='1.6mm' l='35mm' Rc='7.5m
8.00
AG='75deg' b='50mm' fl='19.5mm' fw='3.5mm' h='1.6mm' l='35mm' Rc='8mm' -60 60
-21.00 AG='75deg' b='50mm' fl='19.5mm' fw='3.5mm' h='1.6mm' l='35mm' Rc='8.5m 6.00
4.00
-23.00
-90 90
Ansoft Corporation
2.00 2.50 3.00
XY Plot 1Freq [GHz] 3.50 4.00 HFSSModel2
4.50
-10.00
-120 120
-15.00
dB(S(LumpPort1,LumpPort1))
-150 150
-180
-20.00
Curve Info
-25.00
AG='90deg' h='1.6mm' l='35mm' Rc='7mm'
AG='90deg' h='1.6mm' l='35mm' Rc='7.5m
Figure. 5 Radiation pattern of the antenna
AG='90deg' h='1.6mm' l='35mm' Rc='8mm'
AG='90deg' h='1.6mm' l='35mm' Rc='8.5m
Eplane – red, H plane – blue)
AG='90deg' h='1.6mm' l='35mm' Rc='9mm'
-30.00
Table 1. Band width performance of the antenna
2.00 2.50 3.00 3.50
Freq [GHz]
4.00 4.50
S.No Angle of Rc distance % Band
Figure.2 Return loss plots for Angle AG = 150 Rotation (mm) Width
,
300,450,600,750 for different values of Rc AG(deg)
1 15 7.5 16.47
2 15 8 24.09
3 15 8.5 41.97
4 15 9 44.06
5 30 7 10.81
6 30 7.5 18.35
7 30 8 18.02
8 30 8.5 15.93
9 30 9 13.91
10 45 7 21
11 45 7.5 18
12 45 8.25 10.97
13 90 7 18.02
14 90 7.5 18.35
15 90 8 16.82
16 90 8.5 21.6
90 9 12.8
Figure.3 Bandwidth performance of the antenna Experimental Results
Photographs of top view and bottom vies are show
in figure 6. Fabricated antenna consists centre to centre
distance between two rings is 19mm and angle of rotation
is 15 degrees. VSWR vs frequency plot was shown in
figure 7. From experimental results it is observed that the
impedance band width is from 2 to 3.5 GHZ centered at
2.7 GHZ that is 55%.
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4. Srilakshmi.A, N.V.Koteswara Rao, D.Sreenivasa Rao / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 4, June-July 2012, pp.943-946
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