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Wireless Pers Commun
DOI 10.1007/s11277-012-0730-3
Analysis of L-Shaped Slot Loaded Circular Disk Patch
Antenna for Satellite and Radio Telecommunication
J. A. Ansari · Anurag Mishra · N. P. Yadav · P. Singh ·
B. R. Vishvakarma
© Springer Science+Business Media, LLC. 2012
Abstract In the present paper a dual frequency resonance antenna is achieved by introducing L- shaped slot in circular disk patch. It is analysed by using circuit theory concept.
The resonance frequency is found to be 5.087 and 8.455 GHz and the 10 dB bandwidth of the
proposed antenna for lower and upper resonance frequency is found to be 4.39 and 4.66 %
respectively. It is easy to adjust the higher and lower band by changing the dimensions of
notch and slot introduced in the antenna. The frequency ratio is found to be 1.6621. The gain
and efficiency of the proposed antenna is found to be 9.50 dB at lower resonance however it
is 7.0 dB at upper resonance frequency whereas the efficiency at lower and upper resonance
is found to be 94.6 and 88.2 %.The theoretical results are compared with IE3D simulation
results which are in good agreement.
Keywords Notch loaded patch · Slot loaded patch · Circular diskpatch · Dual band antenna
1 Introduction
Microstrip patch antenna are attractive due to their advantages such as low cost, light weight,
low profile planer configuration and easy to manufacture. Recently, dualband antenna is
found wide applications in wireless and satellite communication. The rapid development
J. A. Ansari · A. Mishra (B) · N. P. Yadav · P. Singh
Department of Electronics & Communication, University of Allahabad, Allahabad 211002, India
e-mail: mishraanurag31@gmail.com
J. A. Ansari
e-mail: jaansari@rediffmail.com
N. P. Yadav
e-mail: nagendralnagendra@gmail.com
P. Singh
e-mail: prabhakarsingh3@gmail.com
B. R. Vishvakarma
Department of Electronics Engineering, I. T. BHU, Varanasi 221005, India
e-mail: brvish@bhu.ac.in
123
J. A. Ansari et al.
in WLAN technology demands the antenna having high performance, dualband and good
radiation characteristics.
During the recent years there has been rapid development in dualband microstrip antenna
due to its wide application in many communication systems.
Number of papers have been reported for dualband operation such as probe fed Circular
microstrip antenna [1], slot loaded circular disk patch antenna [2], slot loaded circular microstrip patch antenna with meandered slits [3], Dualband N-shaped patch antenna [4], Compact
dualband suspended semicircular microstrip antenna with half U-slot [5],Half U-slot loaded
semicircular disk patch antenna [6].
One of the technique to obtain the dualband operation by the way of cutting slots parallel
to the radiating edge of the patch [7,8], cutting square slot in the patch [9,10]. The loading
of the slot on the radiating patch increases the current length that results in lowering fundamental resonance frequency which corresponds to reduced antenna size when compared
with conventional patch antenna at the given operating frequency.
In this investigation we have proposed new patch antenna configuration that shows
dualband operation. The proposed antenna is L-slot loaded circular disk patch antenna that
provides a significant size reduction and good impedance bandwidth. Dual frequency is tuned
by changing the dimensions of the notch and slot. A parametric study has been carried out
using the circuit theory concept by varying the length, width of the notch and slot. Various
antenna parameters are calculated as a function of frequency for different value of notch, slot
length and width.
2 Configuration and Analysis
The side view and top view geometry for the proposed antenna with current distribution are
shown in Fig. 1. Analysis of proposed antenna is carried out by considering the disk patch
of radius ‘a’ equivalent to the square patch of side 2a [11].
The resonance frequency of circular disk patch is given as [12]
fr =
knm c
√
2πae εe
(1)
where knm is the mth zero root of the derivative of Bessel function of order n, c is the velocity
of light and εe is the effective dielectric constant of the substrate [12], ae effective radius of
the circular disk patch.
The effective radius ae of the circular disk is calculated by equating the area of disk to
the expanded rectangular patch with dimension (L e × We ), where L e and We are effective
length and effective width of the rectangular patch and can be calculated by [13]. The equivalent circuit of the circular disk patch is shown in Fig. 2 in which the circuit parameters, i.e.
resistance (R1 ), inductance (L1 ), and capacitance (C1 ) are calculated by [13].
εe εo L W
cos−2 (π xo /L)
2h
1
L1 = 2
ω C1
Qr
R1 =
ωC1
C1 =
(2)
(3)
(4)
in which L = length of the rectangular patch, W = width of the rectangular patch, x 0 =
feed point location along length of the patch, h = thickness of the substrate material
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Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna
X
Feed point
slot
gap between
slot
L-slot loaded
patch
Y
h
notch
ε
r
Foam
Ground plane
Coaxial feed
Top view
Side view
(a)
(b)
Fig. 1 Geometry of L-slot loaded circular disk patch antenna with its current distribution for lower and upper
resonance frequency (a) fr1 = 5.12 GHz, (b) fr2 = 8.39 GHz
and
Qr =
√
c εe
fh
where c = velocity of light, f = design frequency, εe = effective permittivity of the medium which is given by [12]
εe =
εr + 1 εr − 1
10h −1/2
+
1+
2
2
W
where, εr = relative permittivity of the substrate material
Due to two symmetrical L-slot cut in the disk patch resonance behavior changes. The
Analysis of the proposed antenna is classified in two parts.
123
J. A. Ansari et al.
Fig. 2 Equivalent circuit of
circular disk patch
R1
C1
L2
C2
ΔC
ΔL
R1
L1
C1
L1
R2
ΔC
ΔL
(a)
(b)
Fig. 3 (a) Equivalent circuit of circular disk patch due to effect of notch. (b) Modify equivalent circuit disk
patch antenna
2.1 Analysis of Notch Loaded Disk Patch Antenna
When the notch is incorporated in the circular disk patch (L n × Wn ), the two currents flow in
the patch, one is the normal patch current and resonates at the design frequency of the initial
patch; however the other current flows around the notch resulting into second resonance frequency. Discontinuities due to notch incorporated in the patch are considered in terms of an
additional series inductance (L) and series capacitance (C) that modify the equivalent
circuit of circular disk patch as shown in Fig. 3, in which series inductance (L) and series
capacitance (C) can be calculated as [14,15].
hμ0 π
(L n /L)2
8 Ln
C =
.C g
L
L =
and
where μ0 = 4π × 10−7 H/m, L n = depth of the notch, C g = gap capacitance and is given
by [16].
The value of resistance R2 after cutting the notch is calculated by [17]. It may be noted
that the two resonant circuits, one is the initial R1, L1 and C1 of the circular disk patch as
shown in Fig. 2 and another one is after cutting the notch (Fig. 3a) which are modified in
Fig. 3b, are coupled through mutual inductance (L m ) and mutual capacitance (Cm ). Thus the
equivalent circuit of the notch loaded disk patch antenna can be given as shown in Fig. 4a, b.
2.2 Analysis of Slot Loaded Disk Patch Antenna
When the slot is embedded in the patch, having dimension (L S × W S ), it can be analysed by
using the duality relationship between the dipole and slot [18]. The radiation resistance of
123
Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna
Znotch
Zpatch
Lm
Lm
Cm
Cm
Znotch
Zpatch
Zm
(b)
(a)
Fig. 4 (a) Equivalent circuit of coupled notch loaded patch antenna. (b) Modified equivalent notch loaded
resonant circuit
slot on the half disk patch can be given as
⎡
2 ⎤
kLS
k 2 cos θ
π
2
cos
−
cos
2
2
η0 cos α ⎢
⎥
Rr =
⎦dθ
⎣
2π
sin θ
(5)
0
which yields
1
1
Rr = 60 C + ln(k L S ) Ci (k L S ) + sin(k L S ) [Si (2k L S ) 2Si (k L S )] + cos(k L S )
2
2
kLS
× C + ln
+ Ci (2k L S ) 2Ci (k L S )
2
in which C is Euler’s constant = 0.5772/ and Si and Ci are the sine and cosine integrals.
Now the total input impedance of the slot can be given as [19,20].
Z slot =
η02
4Z cy
(6)
in which η0 = 120π and
LS
kLS
Z cy = Rr (k L S ) − j 120 ln
− X r (k L S )
− 1 cot
WS
2
where, Rr is the real part and equivalent to the radiation resistance of slot and Xr is the input
reactance of the slot and given as [20], L s and Ws are length and width of the slot.
Now the equivalent circuit of proposed antenna can be given as shown in Fig. 5. Hence
the total in put impedance of proposed antenna can be calculated from Fig. 5 as,
Z T = (Z ∗ ) +
Z m Z patch
Z patch + Z m
(7)
where
Z∗ =
Z slot Z notch
Z slot + Z notch
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J. A. Ansari et al.
Znotch
ZS1
Z notch
ZPatch
Zm
ZS2
Zslot
(a)
Z patch
Zm
(b)
Fig. 5 (a) Equivalent circuit of Circular disk patch antenna with L-shaped slot. (b) Modified equivalent circuit
of proposed antenna
where Z Patch is the input impedance of the microstrip patch antenna which is calculated
from Fig. 2 as
Z patch =
and
and
in which
Z slot =
Z notch =
L2 =
C2 =
and
Zm =
1
1
R1
+ jωC1 +
1
jωL 1
Z S1 Z S2
Z S1 + Z S2
jω R1 L 2
jωL 2 + R1 − R1 L 2 C2 ω2
L 1 + 2L
C1 C
2C + C
1
1
jωL m +
jωCm
where Lm and Cm are the mutual inductance and mutual capacitance between two resonant
circuits and given as [15].
Lm =
C 2p (L 1 + L 2 ) +
Cm = −
(C1 + C2 ) +
C 2p (L 1 + L 2 )2 + 4C 2p (1 − C 2p )L 1 L 2
2(1 − C 2p )
(C1 + C2 )2 − 4C1 C2 (1 − C −2
p )
2
where C p = √
(8)
(9)
1
Q1 Q2
and Q 1 and Q 2 are quality factors of the two resonant circuits
Now using Eq. (7) one can calculate the various antenna parameters for the proposed
antenna, such as reflection coefficient, VSWR and return loss.
123
Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna
0
Return loss(dB)
-5
Theoretical
Simulated
-10
-15
-20
-25
4
5
6
7
8
9
10
Frequency(GHz)
Fig. 6 Variation of return loss with frequency along with theoretical and simulated results (R = 15 mm,
Ln = 18 mm, Wn = 1 mm, Ls = 9 mm, Ws = 1 mm, h = 1.5 mm, εr = 1.07)
0
Return loss(dB)
-5
-10
Ln=18mm
Ln=19mm
Ln=20mm
-15
-20
-25
4
5
6
7
8
9
10
Frequency(GHz)
Fig. 7 Variation of return loss with frequency for different value of notch depth ‘L n ’
3 Radiation Pattern
The radiation pattern for L-slot loaded circular disk patch antenna is calculated as [19].
E(θ ) = J n k0 RV0 e jk0 r1 [Jn+1 (k0 R sin θ ) − Jn−1 (k0 R sin θ )]. cos nφ
(10)
E(φ) = J n k0 RV0 e− jk0 r1 [Jn+1 (k0 R sin θ ) − Jn−1 (k0 R sin θ )]. cos θ sin nφ
(11)
where V0 = radiating edge voltage = h E 0 Jn (R), r1 = distance of an arbitrary far-field
point, R = radius of half circular fed disk patch
123
J. A. Ansari et al.
0
Return loss(dB)
-5
-10
Wn=1.0mm
Wn=1.5mm
Wn=2.0mm
-15
-20
-25
4
5
6
7
8
9
10
Frequency(GHz)
Fig. 8 Variation of return loss with frequency for different value of notch width ‘Wn ’
Table 1 Calculated bandwidth for different value of notch depth
Notch depth
Lower resonance frequency
(Ln ) mm
Bandwidth
(MHz)
Centre
frequency
( GHz)
Bandwidth (%)
Bandwidth
(MHz)
Upper resonance frequency
Centre
frequency
( GHz)
Bandwidth (%)
18.0
223
5.087
4.39
394
8.455
4.66
19.0
258
5.392
5.03
323
8.443
3.90
20.0
290
5.609
5.47
282
8.247
3.48
4 Design and Specifications
Design specifications for L-shaped slot loaded circular disk patch antenna
Substrate material
Foam
Relative permittivity of the substrate (εr )
Thickness of the dielectric substrate (h)
Radius of the half disk patch (R)
Depth of the notch (L n )
Width of the notch (Wn )
Length of the slot (L s )
Width of the slot (Ws )
Distance between L-slot (s)
Feed location (x0 , y0 )
1.07
2.5 mm
15.0 mm
18.0 mm
1.0 mm
9.0 mm
1.0 mm
2.0 mm
(0.0, 3.6 mm)
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Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna
Table 2 Calculated bandwidth for different value of notch width
Notch width
Lower resonance frequency
(Wn ) mm
Bandwidth
(MHz)
Centre
frequency
( GHz)
Bandwidth (%)
Bandwidth
(MHz)
Upper resonance frequency
Centre
frequency
( GHz)
Bandwidth (%)
1.0
223
5.087
4.39
394
8.455
4.66
1.5
196
4.989
3.93
328
8.184
4.01
2.0
192
4.897
3.90
306
7.919
3.86
0
Return loss(dB)
-5
Ls=9.0mm
Ls=8.5mm
Ls=8.0mm
-10
-15
-20
-25
4
5
6
7
8
9
10
Frequency(GHz)
Fig. 9 Variation of return loss with frequency for different value of slot length ‘L s ’
0
Return loss(dB)
-5
-10
Ws=1.0mm
Ws=1.5mm
Ws=2.0mm
-15
-20
-25
4
5
6
7
8
9
10
Frequency(GHz)
Fig. 10 Variation of return loss with frequency for different value of slot width ‘Ws ’
123
J. A. Ansari et al.
Table 3 Calculated bandwidth for different value of slot length
Slot length
Lower resonance frequency
Upper resonance frequency
(LS ) mm
Bandwidth
(MHz)
Centre
frequency
( GHz)
Bandwidth (%)
Bandwidth
(MHz)
Centre
frequency
( GHz)
Bandwidth (%)
9.0
223
5.087
4.39
394
8.455
4.66
8.5
229
4.990
4.59
436
8.680
4.95
8.0
233
4.855
4.80
469
7.909
5.27
Table 4 Calculated bandwidth for different value of slot width
Slot width
Lower resonance frequency
Upper resonance frequency
() mm
Bandwidth
(MHz)
Centre
frequency
( GHz)
Bandwidth (%)
Bandwidth
(MHz)
Centre
frequency
( GHz)
Bandwidth (%)
1.0
223
5.087
4.39
394
8.455
4.66
1.5
257
5.260
4.89
434
8.815
4.92
2.0
287
5.485
5.27
460
9.220
4.99
0
Return loss(dB)
-5
-10
s=2.0mm
s=2.4mm
s=2.8mm
s=3.2mm
-15
-20
-25
4
5
6
7
8
9
10
Frequency(GHz)
Fig. 11 Variation of return loss with frequency for different value of gap of L-slot ‘s’
5 Results and Discussion
The variation of return loss with frequency for L-slot loaded circular disk patch antenna is
shown in Fig. 6 along with simulated results using IE3D [20]. From the figure, it is observed
that the antenna resonates at two frequencies fr1 = 5.087 GHz and fr2 = 8.455 GHz (simu-
123
Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna
1.68
1.66
Frequency ratio
1.64
Theoretical
Simulated
1.62
1.6
1.58
1.56
1.54
1.52
1.5
1.48
18
18.5
19
19.5
20
Notch depth(mm)
Fig. 12 Variation of frequency ratio for different value of notch depth
1.68
1.67
Theoretical
Simulated
Frequency ratio
1.66
1.65
1.64
1.63
1.62
1.61
1.6
1.59
1.58
1
1.2
1.4
1.6
1.8
2
Notch width(mm)
Fig. 13 Variation of frequency ratio for different value of notch width
lated fr1 = 5.12 GHz, fr2 = 8.398 GHz) and 10 dB bandwidth is found to be 4.39 % for lower
resonance whereas it is 4.66 % for upper resonance frequency (simulated 4.28 and 4.45 %
respectively). Frequency ratio of upper to lower resonance frequency is found to be 1.6621
(simulated 1.6402). The theoretical results are in good agreement with simulated results. It is
observed that both the theoretical and simulated results for bandwidth are in good agreement
at lower and upper resonance frequency.
Figures 7 and 8, shows the variation of return loss with frequency for the different value
of notch depth (L n ) and notch width (Wn ). From Fig. 7, it is found that lower and upper
resonance frequency shifts towards lower side as the notch depth increases but corresponding
123
J. A. Ansari et al.
2
1.95
Theoretical
Simulated
Frequency ratio
1.9
1.85
1.8
1.75
1.7
1.65
1.6
1.55
1.5
8
8.2
8.4
8.6
8.8
9
Slot length(mm)
Fig. 14 Variation of frequency ratio for different value of slot length
Theoretical
Simulated
Frequency ratio
1.7
1.68
1.66
1.64
1.62
1.6
1
1.2
1.4
1.6
1.8
2
slot width(mm)
Fig. 15 Variation of frequency ratio for different value of slot width
bandwidth decreases as shown in (Table 1), while increasing the notch width higher resonance frequency shifts to right side and lower resonance frequency shifts to left side. The
variation of bandwidth for different notch width is shown in Table 2.
The variation of return loss with frequency with slot length (L s ) and slot width (Ws ) is
shown in Figs. 9 and 10. It is observed that for decreasing the value of slot length, higher
resonance frequency shifts towards higher side whereas the lower resonance shifts slightly
to lower side and bandwidth for both the resonances increases as shown in Table 3, while
increasing slot width both the resonance frequencies shift to higher side. The calculated
bandwidth for different slot width is shown in Table 4. Further increasing the value of the
length and width of the slot dualband behaviour will change.
123
Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna
Relative radiative power(dB)
0
-2
-4
Theoretical
Simulated
-6
-8
-10
-12
-50
0
50
Angle(degree)
Fig. 16 Radiation pattern of L-shaped slot loaded circular disk patch antenna for lower resonance frequency
Relative radiative power(dB)
0
-2
-4
Theoretical
Simulated
-6
-8
-10
-12
-80
-60
-40
-20
0
20
40
60
80
Angle(degree)
Fig. 17 Radiation pattern of L-shaped slot loaded circular disk patch antenna for upper resonance frequency
Figure 11 shows the variation of return loss with frequency for different value of gap (s)
of the L-slot. It is observed that for increasing the value of gap between the L-slot both the
resonance frequency shift to right side.
Figures 12 and 13, shows that the ratio of resonance frequencies f2 /f1 for different value
of notch depth and notch width. It is found that the resonance frequency decreases with
increasing the notch depth, while it is directly proportional to notch width.
Figures 14 and 15 shows the ratio of resonance frequencies f2 /f1 for different value of
slot length and slot width. It is observed that the ratio of frequency increases with decreasing
the value of slot length, while it increases with increasing the slot width.
123
J. A. Ansari et al.
10
8
6
Gain(dB)
4
2
0
-2
Theoretical
Simulated
-4
-6
-8
3
4
5
6
7
8
9
10
Frequency(GHz)
Fig. 18 Variation of gain with frequency for L-shaped slot loaded circular disk patch antenna
100
90
Theoretical
Simulated
80
Efficiency(%)
70
60
50
40
30
20
10
0
3
4
5
6
7
8
9
10
Frequency(GHz)
Fig. 19 Variation of efficiency with frequency for L-shaped slot loaded circular disk patch antenna
Radiation pattern for proposed antenna is shown in Figs. 16 and 17. The theoretical results
show good agreement with the simulated results for lower and upper resonance frequency
however there is minute deviation in the beam widths.
The gain and efficiency of the proposed antenna are shown in Figs. 18 and 19. From the
figure, it is observed that the gain of the antenna at two frequencies is 9.50 and 7 dB (simulated 9.8 dB and GHz, 6.2 dB) and efficiency is 94.6 % for lower resonance whereas it is
88.2 % for upper resonance frequency (simulated 91 and 79.6 %).
123
Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna
6 Conclusion
From the analysis it is concluded that compact L-shaped slot loaded circular disk patch
antenna can operate at two resonance frequencies 5.087/8.445 GHz and useful for dualband
operation. The resonance frequency is highly dependent on the notch and slot dimensions
with gap of the slot.
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Author Biographies
J. A. Ansari was born in 1966 in Gahmar, Ghazipur (U.P.), India. He
received the B.Sc. and B.Tech. degrees in Electronics and Telecommunications from University of Allahabad, Allahabad, India, in 1987
and 1989. The M.Tech degree in Communication Systems from the Institute of Technology, Banaras Hindu University (BHU), Varanasi, India, in 1991, and the Ph.D. degree from Mahatma Gandhi Chitrakoot
Gramodaya Vishvavidyalaya, Chitrakoot (Satna), India, in 2000. He
has published 92 papers in different national and international journals
and conference proceedings. His current area of research is microstrip
antenna, millimeter wave, and fiber optics. He is presently working as
a Professor with the Department of Electronics and Communication,
University of Allahabad.
Anurag Mishra was born in Varanasi (U.P.), India in 1984. He
received his B.Sc. and M.Sc. (physics specialization in Electronics)
Degree from University of Allahabad 2004 and 2006 respectively. He
is a research scholar in Department of Electronics and Communication,
University of Allahabad, Allahabad (India). He published more than 44
papers in different international journals and international and national
conferences. He is currently working on microstrip antenna and millimeter wave propogation with wireless and biomedical application.
N. P. Yadav was born in village Gorain, Varanasi (U.P.), India in 1984.
He received his B.Sc. and M.Sc. (Electronics) degree, from V. B. S.
Purvanchal University in 2004 and 2006 respectively. He is a research
scholar in Department of Electronics and Communication, University
of Allahabad, Allahabad (India). He published more than 50 papers in
different international journals, international and national conferences.
He is currently working on microstrip antenna.
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Analysis of L-Shaped Slot Loaded Circular Disk Patch Antenna
P. Singh was born in village Semra, Chandauli (U.P.), India in
1984. He received his B.Sc. and M.Sc. (Electronics) degree, from
V. B. S. Purvanchal University in 2004 and 2006 respectively. He is a
research scholar in Department of Electronics and Communication,
University of Allahabad, Allahabad (India). He published more than
45 papers in different international journals, international and national
conferences. He is currently working on microstrip antenna.
B. R. Vishvakarma was born in Dhananjaipur, Jaunpur (U.P.),
India in 1944. He received the B.Sc. (Engg.), M.Sc. (Engg.), and
Ph.D. degrees in electronics engineering from Banaras Hindu University (BHU), Varanasi, India, in 1969, 1972, and 1977, respectively.
From 1973 to 1975, he was a Senior Research Fellow with the Department of Electronics Engineering, Institute of Technology (IT), BHU,
where he carried out research work on microwave scattering and ferrite
devices. In 1984, he rejoined the Department of Electronics Engineering, IT, BHU, as a reader, where he is presently working as a Professor
of electronics engineering, His professional interests include the area of
microwave and millimeter wave propagation, radar, scattering, ferrite
devices, electronic scanning antennas, microstrip antennas, piezoelectric effects in bone, electromagnetic interaction (both energetic and informational) with biographical media. He has published more than 190
research papers in international reference journals and proceedings. He
has also published one monograph on microwave ferrite junction circulator and a textbook Electromagnetic Fields and Applications. His two papers on microwave/millimeter
wave propagation were awarded a Certificate of Merit (1993, 1994) and a paper on microstrip antenna was
awarded the Institution Medal of Institution of Engineers (India) for 1996–1997.
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