Comparative study of slot loaded rectangular and triangular microstrip array antennas

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Special Issue: 03 | May-2014 | NCRIET-2014, Available @ http://www.ijret.org 208
COMPARATIVE STUDY OF SLOT LOADED RECTANGULAR AND
TRIANGULAR MICROSTRIP ARRAY ANTENNAS
G M Pushpanjali1
, R B Konda2
, S K Sajjan3
1
Asst. Prof., Dept. of Physics, Central University of Karnataka, Gulbarga
2
Asst. Prof., Dept. of Electronics, Smt. V. G. Degree College for Women, Gulbarga 585 102
3
Asso. Prof., Dept. of Electronics, S.V.M, Arts, Sc. and Comm. College, Ilkal (Karnataka) 587125
Abstract
In this paper we have presented the comparative study and theoretical validation of two element slot loaded rectangular microstrip
array antenna (TS-RMAA) and two element slot loaded equilateral triangular microstrip array antenna (TS-ETMAA), fed by
corporate feed technique illustrating wide band operation. The experimental results reveal that, the impedance bandwidth of TS-
RMAA is 6.54% (i.e., 700 MHz) and the impedance bandwidth of TS-ETMAA is 7.35% (i.e., 820MHz). The impedance bandwidth of
TS-ETMAA is 1.12 times more than the impedance bandwidth of TS-RMAA. The theoretical impedance bandwidth is determined to
compare the experimental impedance bandwidth for validation. The theoretical and experimental impedance bandwidth is in close
agreement with each other. The wide band operation of the antenna may find application in communication system.
Keywords: Array antenna, wide band microstrip antenna, triangular microstrip antenna.
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1. INTRODUCTION
With the saturation of low frequency bands, the operating
frequencies of modern communication systems have risen and
planar antennas have become more attractive. Among them,
microstrip antennas form a special category on which
considerable research work has been conducted. However
microstrip antennas inherently have a narrow impedance
bandwidth and its enhancement is usually demanded for
practical applications. On the other hand, wide band antenna
with small physical size and good performance are an
oncoming challenge to meet the needs of integration, cost and
efficiency of the emerging wireless world.
One of the most attractive features of the equilateral triangular
microstrip antenna (ETMSA) is that, the area necessary for the
patch becomes about half as large as that of a nearly
rectangular or square microstrip antenna designed for the same
frequency [1]. In view of this an effort is made to enhance the
impedance bandwidth of the antenna by reducing the area of
the radiating patch.
2. DESCRIPTION OF THE ANTENNA
GEOMETRY
The antennas are sketched by using computer software Auto-
CAD and fabricated on low cost glass epoxy substrate material
of thickness h =1.66mm and permittivity r = 4.2. The
radiating elements of TS-RMAA and TS-ETMAA shown
respectively in Fig.1 and Fig.2 are fed by using corporate feed
technique.
Fig – 1: Designed geometry of TS-RMA
Fig – 2: Designed geometry of TS-ETMAA
This technique has been selected because of its simplicity and
it can be simultaneously fabricated along with the antenna
elements. In Fig. 1 and Fig. 2 the distance between the two
radiating elements DR is kept at 3o/4 in order to add the
radiated power in free space by individual elements to
improve antenna parameters. However, the DR is taken in
terms of multiple of half wavelength. But in this case 3o/4
has been selected in order to accommodate corporate feed
arrangements between the two radiating elements. The
corporate feed arrangement consists of matching transformer,
quarter wave transformer, microstrip bend and two way power

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divider used for better impedance matching between feed and
radiating element which reduces the loss in the feed line At the
tip of microstrip line feed [2] a 50  coaxial SMA co-axial
connector is used for feeding the microwave power.
3. EXPERIMENTAL RESULTS
The impedance bandwidth over return loss less than –10dB for
the proposed antennas is measured for X-band frequencies.
The measurement is taken on Vector Network Analyzer
(Rohde & Schwarz, Germany make ZVK model).
The variation of return loss versus frequency of TS-RMAA
and TS-ETMAA is shown in Fig. 3 and 4 respectively. From
these graphs the impedance bandwidth is determined by using
the equation:
BW =
  10012





 
cf
ff
%
Where, f1 and f2 are the lower and upper cut off frequency of
the band respectively, when its return loss becomes –10dB,
and fc is a centre frequency between f1 and f2. The
experimental result shows the impedance bandwidth of TS-
RMAA is 6.54% and the impedance bandwidth of TS-
ETMAA is 7.35%.
10.0 10.2 10.4 10.6 10.8 11.0 11.2
-40
-35
-30
-25
-20
-15
-10
-5
6.54%
700 MHz
f2
f1
RETURNLOSS,dB
FREQUENCY, GHz
Fig - 3: Variation of return loss versus frequency of TS-
RMAA
Fig - 4: Variation of return loss versus frequency of TS-
ETMAA
4. THEORETICAL RESULTS
The proposed antennas TS-RMAA and TS-ETMAA have
been designed for TE10 mode.
The expression derived by Girish Kumar and K. P. Ray [3] for
the calculation of percentage impedance bandwidth are in
terms of patch dimensions and substrate parameters for
conventional rectangular microstrip antenna and is given by,
 
0 r
A×h W
Impedance Bandwidth % = ×
Lλ ε
 
 
  
(1)
Where
h = thickness of the substrate
rε = relative permittivity of the substrate
W = width of the patch
L = length of the patch
0λ = free-space wavelength
A = correction factor
The correction factor „A‟ changes as the value of factor
0 r
h
λ ε
 
 
  
changes [4], which is given by;
A = 180 for
0 r
h
0.045
λ ε
 
 
  
A = 200 for
0 r
h
0.045 0.075
λ ε
 
  
  
A = 220 for
0 r
h
0.075
λ ε
 
 
  
In the present investigation the value of correction factor A is
taken as 180 because the calculated value of
0 r
h
λ ε
 
 
  
TS-
RMAA and TS-ETMAA is lesser than 0.045 determined for
the known value of h, 0λ and r.
Since the expression (1) given by [3] is for single element
RMSA. This equation is extended for calculating the
impedance bandwidth of RMAAs by multiplying the ratio W
L
by n . The extended equation becomes,
 
0 r
A×h W
Impedance Bandwidth % = × n×
Lλ ε
 
 
  
(2)
10.6 10.8 11.0 11.2 11.4 11.6
-35
-30
-25
-20
-15
-10
-5
0
BW
RETURNLOSS,dB
FREQUENCY, GHz

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Where, n = number of rectangular radiating patches in
RMAAs.
If the radiating elements are equilateral triangular in shape The
equation (1) is converted for equilateral triangular microstrip
antenna and arrays by replacing the W/L ratio with (n × Se).
The modified equation for ETMA is given by
  e
0 r
A×h
Impedance Bandwidth % = × n×S
λ ε
 
 
  
(3)
Where, Se = effective side length of the equilateral triangular
radiating patch and
n = number of radiating patches.
In equation (3) the value of Se is given by the formula [4]
e
e
4h
S = S+
ε
(4)
Where
S = side length of the equilateral triangular microstrip patch
e = effective dielectric constant
In TS-RMAA and TS-ETMAA the rectangular slots are
loaded at the center of the radiating elements The insertion of
slot changes the impedance of conducting patch. Therefore for
determining the impedance bandwidth of area of slot loaded
rectangular and triangular microstrip radiating patches (ASP)
and capacitance of the slot (CS) are taken into consideration.
The CS is calculated with the help of the transmission line
model [2]. This analytical technique is based on equivalent
magnetic current distribution around the patch edges which is
similar to slot antennas.
The change of impedance of patch mainly depends upon the
area of slot and its location as the impedance of the patch is
non-linear [3]. The effective resonance characteristics due to
change of impedance is given by multiplying the ratio W/L by
ASP in equation 2 and by Se in equation 3. Since slots are on
the radiating patches separated by the ground plane by
substrate of thickness h The slot behaves as capacitor and
resonates as secondary resonator to the main patch. The
resonance of slot if close to the main patch which causes
enhancement in the impedance bandwidth The capacitive
associated to the slot is CS. The term CS is added to equation 2
and 3 to determine total resonance of TS-RMAA and TS-
ETMAA. The capacitance parameter CS associated to the slot
is evaluated using the transmission line model [2] given by;
eff
S
0
Δl ε
C =
c×Z
(5)
Where, l is the extension length and eff is the effective
dielectric constant. Hence equation (2) for TS-RMAA
becomes,
  SP S
0 r
A×h W
Impedance Bandwidth % = × n A C
Lλ ε
  
   
  
(6)
And for TS-ETMAA is,
  e sp s
0 r
A×h
Impedance Bandwidth % = × 2×S ×A + C
λ ε
  
       (7)
Where
n = 2 as proposed antennas consists of two radiating elements.
ASP = area of the slot loaded patch excluding the area of
rectangular slot
CS = capacitance of the slot
The value of Asp in equation (6 and 7) is calculated by using
the formula
SP P SA = A A (8)
Where
Ap = area of patches.
As = area of rectangular slots
The value of AP is for the given antennas are determined using
basic formulae for rectangular and equilateral triangular
geometries. In the above equation 8, AS is obtained by the
formula;
S S SA = L × W (9)
Where
LS = length of the rectangular slot
WS = width of the rectangular slot
The impedance bandwidth of TS-RMAA and TS-ETMAA is
calculated using the equation (6) and (7) is recorded in Table
1.
5. CONCLUSIONS
From the detailed experimental study it is found that, the
proposed antenna TS-ETMAA is quite capable of enhancing
the impedance bandwidth by 12.38% and compactness of
10.71% when compared to TS-RMAA. This shows the
superiority of ETMSA in enhancing the impedance
bandwidth. Experimental impedance bandwidth is verified
theoretically. The theoretical and experimental impedance
bandwidth is in close agreement with each other. These

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antennas are simple in their geometries and the feed line can
be fabricated along with the radiating patches. Such antennas
may find applications in the microwave communication
systems.
Table -1: Various antenna parameters
Antennas
Parameters Impedance bandwidth (%)
Minimum return
loss in dB
VSWR
HPBW in
dB
Gain
in dB
Nature of
impedance
bandwidth
Theoretical Experimental
TS-RMAA -38.61 1.02 43.91 4.7 Single band 5.55 6.54
TS-ETMAA -35.26 1.04 42.34 4.14 Single band 7.12 7.35
REFERENCES
[1] Pushpanjali G.M., Konda R.B., Mulgi S.N., Satnoor
S.K., and Hunagund P.V., “Equilateral triangular
microstrip array antenna for broadband operation”,
International Journal of Microwave and Optical
Technology Letters, Vol. 50, pp. 1834-1837, July 2008.
[2] Bhal I J and Bhartia P, Microstrip Slot Antennas,
Microstrip Antennas, Dedham, MA: Artech House, pp.
221-245, 1981.
[3] Girish Kumar and K. P. Ray, Broadband Microstrip
Antennas, Norwood, MA: Artech House, 2003.
[4] Constantine A Balanis, Arrays: Linear, Planar, and
Circular, Antenna Theory Analysis and Design, John
Wiley & Sons Inc., New York, pp. 204-282, 1982.
BIOGRAPHIES
Dr. G. M. Pushpanjali, is presently
working as an Assistant Professor at
Department of Physics, Central University of
Karnataka, Gulbarga, India. She is an active
researcher in the area of microwave
communication and applied electronics with the teaching and
research experience of more than 10 years. In recognition she
is awarded with best research paper award for her work in
antenna design. Along with academics she holds national
recognition for social service and welfare.
Dr. R B Konda received his M.Sc and Ph.D
degree from Gulbarga University, Gulbarga
in the field of Electronics in the year 1992
and 2009 respectively. He is working as
Asst. Professor in Electronics in Smt V. G.
Degree College for Women, Gulbarga since 1992. He is an
active researcher in the field of Microwave Electronics.
Sri. S. K.Sajjan, received his M.Sc degree
from Gulbarga University, Gulbarga in
Electronics in the year 1991. He is working
as Associate Professor in the Dept. of
Electronics, S.V.M, Arts, Sc. and Comm.
College, Ilkal since 1991. He is an active researcher in the
field of Microwave Electronics.

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