Proceedings of Asia-Pacific Microwave Conference 2007
Modified
Slotted Patch Electromagnetic Band Gap
for Antenna Array Application
0. Ayopl, M.K.A Rahiml, T. Masril, M.N.A. Karim', M.Z.A. Abdul Aziz2
'Wireless Communication Centre,
Faculty of Electrical Engineering,
Universiti teknologi Malaysia,
813 10 Skudai Johore Baharu.
2Faculty of Electronic and Computer Engineering
Universiti Teknikal Malaysia Melaka,
75450 Ayer Keroh, Melaka.
Abstract- A modified slotted patch EBG structure has been
investigated by measuring the forward transmission coefficient,
S21. The thickness and dielectric constant of the substrate, the
size and the gap of the elements in EBG structure has been
modified and simulated to see the S21 value and followed by a
discussion of the design and the evaluation of the structure itself.
The simulation process was carried out using microwave office
2006 software. The 3 by 3 Modified Slotted patch EBG structures
which has 11 mm x 11 mm elements size was fabricated using
inexpensive Fire Retardant-4 (FR4) board, using wet etching
techniques. The stimulated and measured S21 result shows the
band gap of the structure, which are found to be between 2.24
GHz and 2.6 GHz at -20 dB. This structure is then incorporated
into a 2 by 2 rectangular microstrip antenna array, operating at
2.4. The result shows that the radiation pattern improved with
reducing side and back lobe with an extra gain of 1 dB compared
with the antenna without the EBG structure.
II.
PARAMETRIC STUDY OF THE MODIFIED SLOTTED PATCH
EBG STRUCTURE
This paper is produced to study the characteristic of
the Modified Slotted patch EBG structure. The parameters of
the EBG structure such as size of the EBG lattice, the
thickness of the substrate, the dielectric constant, and the gap
between elements in EBG lattice are the parameters that will
be investigated to determine the band gap frequency. The
value of S21 has been measured to investigate the frequency
band gap for the EBG structure. Figure 1 (a) shows the basic
structure of the Modified Slotted patch EBG structure. Slotted
patch EBG structure has been chosen due to the compact size
and the ability of tuning the band gap frequency by adjusting
the slot size.
Keywords: Electromagnetic Band Gap (EBG), microstrip
antenna array, slottedpatch, periodic structure
I.
INTRODUCTION
Surface wave is the main problem in microstrip
antenna design. This problem reduces the antenna's efficiency
due to the large side and back radiation [1]. The front radiation
is degrading, resulting from the enhancement of side and back
radiation. The gain of the antenna is also reducing [2, 3]. To
overcome this problem, the Electromagnetic Band Gap (EBG)
structure has been created to suppress the propagation of the
surface wave within the substrate [4]. This structure has
become attractive in antenna application in recent years.
Generally, the EBG structure can be realized by drilling a
periodic pattern of holes in the substrate or by etching a
periodic pattern of circles on the ground plane or by
introducing a lattice of metallic pads connected to the ground
with vias [5]. The EBG structure that has a lattice of metallic
pads without using any vias has been created. The EBG
structure should have a band gap frequency in the range of the
operational frequency of the antenna. The frequency band gap
of the EBG structure is investigated by measure the S21 value
below -20 dB. This band gap of frequency is the result of the
equivalent LC network in the EBG structure itself [6].
slot
patch
(a)
(b)
Figure 1: (a) One element of Modified slotted patch EBG structure and
(b) the 3D view of Modified Slotted patch EBG structure
A.
The effect of the Element's Size on the EBG Structure
The first parameter has been investigated is the effect
of the size of elements in 3 by 3 Modified slotted patch EBG
structure to the band gap frequency. The structure has been
designed based on the Fire Retardant-4 (FR4) board which has
relative permittivity 4.6, thickness 1.6 mm and 0.035 mm
thickness of copper and ground plane. Figure 1 (b) shows the
1-4244-0749-4/07/$20.00 @2007 IEEE.
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3D view of the 3 by 3 Modified slotted EBG structure. Based
on the above figure, a transmission line is placed on the
second substrate. The second substrate which has thickness of
0.5 mm is placed on the Modified Slotted patch EBG structure
which has thickness of 1.6 mm. The simulation has been done
by transmitting a signal in a certain range of frequency
through the transmission line. The result is shown in table 1
below.
Table 1 shows the size of the element in Modified Slotted
EBG structure and the band gap frequency respectively.
TABLE 1: BAND GAP FREQUENCY FOR DIFFERENT SIZE ELEMENT.
Patch size
Slot size
5mmx5mm
6mmx6mm
7mmx7mm
8mmx8mm
9mmx9mm
lOmmxlOmm
llmmxllmm
2mmxO.5mm
2mmxlmm
2.5mmxlmm
3mmxlmm
3mmxlmm
4mmxlmm
5mmxlmm
Band gap frequency
(GHz)
3.74 -5.31
3.22 -4.47
2.97 -3.84
2.66 -3.69
2.46 -3.23
2.19 -2.96
1.98 -2.67
From table 2, the band
gap frequency is reduced to a lower
frequency when the dielectric constant of the substrate is
increased.
C.
The Effect ofGap between Elements on the EBG
Structure
Figure 2 shows the structure of 3 by 3 Modified Slotted
patch EBG structure. Generally, the gap between elements
will introduce capacitance effect in overall EBG structure. The
band gap frequency is measured for the different gap between
elements. The simulated result is shown in figure 3.
gap
Figure
2:
patch EBG
m m structure
-40~~ by 3 Modified Slotted
~
A 2D view of 3
.............
0
Base on the table 1, the band gap frequency reduce to a lower
frequency for a larger size of the elements in modified slotted
EBG structure. To shift the band gap frequency to higher
frequency, more capacitance is introduced means that the slot
size should be increased.
-10
-20
2~~~~~~~05mm
40
3
560
l
mm
4
mm
5
mm
-60
B.
The Effect of Dielectric Constant on the EBG Structure
Table 2 shows the characteristic of the Modified
Slotted EBG structure base on the forward transmission
coefficient, S21 when using the different value of dielectric
constant. The simulation process is done on the structure like
in figure 2. Referring to the figure 2, the EBG structure is
designed on the 1.6 mm thick substrate. On the EBG structure,
the 0.5 mm thick substrate is used to place the transmission
line. A signal in a certain range of frequency is supplied
through the transmission line. The result is presented in a table
2 below.
TABLE 2: BAND GAP FREQUENCY FOR DIFFERENT DIELECTRIC CONSTANT
Dielectric constant,
2
Band gap frequency, GHz
2.92 - 3.85
3
2.43 - 3.24
4.6
1.98 - 2.64
5
1.99 - 2.52
6
1.75 - 2.33
7
1.62 -2.15
8
1.53 - 2.02
9
1.43- 1.92
10
1.39- 1.81
0.5
1.0
1.5
2.0
2.5
3.0
Frequency, GHz
3.5
4.0
=L
4.5
Figure 3: The band gap frequency for different gap size.
Figure 3 shows the band gap frequency for the different gap
size. From the figure, the different gap sizes do not give much
different to the characteristic of the band gap frequency. All
the structure show the band gap frequency covers the
frequency of interest at 2.4 GHz.
D. The Effect of the Thickness in EBG Structure
Referring to the figure 1 (b), the thickness of the
second material on the EBG structure, h2 has been adjusted
and simulated in different thickness of the substrate. The
simulated result is presented in term of graph in figure 4.
1.4
1.6
1.8
2.0
2.2
2.4
2.6
Frequency (GHz)
2.8
3.0
32
Figure 4: The band gap frequency for different substrate thickness.
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From figure 4, the thickness of the substrate on the
EBG structure plays an important role to determine the band
gap frequency of the EBG structure. The enhancement of the
thickness of the second substrate on the EBG structure will
reduce the range of the band gap frequency. It means that the
EBG structure is only sufficient to the thicker antenna
substrate.
-1
-26
ioq
-30
-vo
-o0
-46
III.
DEVELOPMENT OF THE MODIFIED SLOTTED PATCH
EBG STRUCTURE
The 3 by 3 Modified slotted patch EBG structure
which a patch size of 11 mm x 11 mm has been selected to do
the analysis in both simulation and fabrication. Before starting
the fabrication process, the simulation process should prove
that the structure can suppress the propagation of the surface
wave in the band gap frequency. Figure 5 shows the simulated
result for the forward transmission coefficient, S21 and the
return loss, SI, respectively.
0
......
I
-30
-40
S21
Si i
-50
-60
-70
1.4
1.6
1.6
2.0 2.2 2.4 2.6
Frequency (GHz)
easuremert
2.8
3.0
3.2
Figure 7: The simulated and measured result for 3 by 3 Modified Slotted patch
EBG structure
Figure 7 shows the simulated and measured result for 3 by
3 Modified Slotted patch EBG structure which has 11 mm x
11 mm element's size. From the above graph, the band gap
frequency is narrower than the simulated result. The measured
result shows that the band gap frequency extend from 2.24
GHz up to 2.6 GHz, but it still covers the frequency of interest
at 2.4 GHz.
t
-20
co
m
IV. IMPLEMENTATION OF THE MODIFIED SLOTTED PATCH
EBG STRUCTURE IN 2 BY 2 MICROSTRIP ANTENNA ARRAY.
..
-10
q-
-70
I
1.4
1.6
1.8
2.0
2.2
2.4
2.6
Frequency (GHz)
2.8
3.0
i
3.2
The 11 mm x 11 mm patch size has been
implemented to the 2 by 2 microstrip antenna array to see the
effect of the EBG structure on the performance of the
microstrip antenna array. Figure 8 shows the 2 by 2 microstrip
antenna array with and without Modified slotted patch EBG
structure.
Figure 5: The simulated result for SI, and S21
From the graph, the Modified slotted patch EBG structure has
a band gap frequency measured at S21 at -20 dB and below is
from 1.98 GHz to 2.67 GHz. At this band gap frequency, the
value of SI, is almost near to 0 dB indicates that the signal in
the frequency band gap cannot propagate on the EBG surface.
This Modified slotted patch EBG structure has been fabricated
and measured to see the performance. Figure 6 shows the 3 by
3 Slotted Patch EBG structures that has been fabricated and
measured. The performance of this EBG structure is shown in
figure 7.
Figure 8: A 2 by 2 microstrip array antenna with and without the Modified
Slotted patch EBG structure.
Figure 6: The 3 by 3 Modified Slotted Patch EBG structure
Figure 9 shows the measured E-co polarization for 2 by 2
microstrip antenna array as shown in figure 8. From the figure,
the maximum power received is -22 dBm for the antenna
without modified slotted patch EBG structure. By surrounding
the same antenna with modified slotted patch EBG structure,
the power received is -21 dBm. The 1 dB increment is noticed.
The side and back radiation for the 2 by 2 microstrip antenna
array with EBG structure is reduced.
Figure 10 shows the comparison of measured H-Co
polarization for 2 by 2 microstrip antenna array with and
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without Modified Slotted patch EBG structure at a frequency
of 2.4 GHz. From the figure, the maximum power received is 23 dBm for the antenna without slotted patch EBG structure.
The power received increase to -22 dBm for the antenna with
slotted patch EBG structure. The side lobe and back lobe for
the 2 by 2 microstrip array antenna with EBG structure is
reduced.
330~
P-.60
.k
\.i
V.
CONCLUSION
The characteristic of the Modified Slotted patch EBG
structure has been presented. The EBG structure is depending
on the types of material used which has certain dielectric
constant, the thickness of the substrate, the gap between
elements and the different size of elements in EBG structure.
Next, the integration of the Modified Slotted patch EBG
structure with the microstrip antenna array has improved the
performance of the antenna. The radiation patterns of the
antenna with modified slotted EBG structure in term of the
side and back radiation are better compared to the microstrip
antenna array without modified slotted patch EBG structure.
By using the EBG structure, the surface wave effect is
reduced, resulting to the improvement of the antenna
performance.
90
-30 -20
270 -20 -30 -40
240
The authors would like to thanks the Ministry of Science,
Technology and Innovation (MOSTI) of Malaysia for
supporting this works.
Sg120
.X
-30
-30
210
-
ACKNOWLEDGEMENTS
2
1
without EBG vs
degree
-with EBG vs d~eyee
1
150
REFERENCES
Figure 9: Measured E-Co polarization for 2 by 2 microstrip antenna array
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[2]
[3]
300,
270
-20
V
-30
-30
240
60
-20
[4]
90
120
-30
210
-twthout EBO vs degree
150
[5]
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-I-withEBvs de3e
Figure 10: Measured H-Co polarization for 2 by 2 microstrip antenna array
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