JOURNAL OF TELECOMMUNICATIONS, VOLUME 6, ISSUE 1, DECEMBER 2010
22
Compact Multisize Electromagnetic Bandgap
Structures with Wide Stopband
K Kamardin, M. K. A. Rahim, N. A. Samsuri and M. A. R Osman
Abstract— Electromagnetic Band Gap (EBG) has become one of the most promising technologies to be applied for antenna
applications. Research in EBG field has recently received remarkable interest and potentially destined as the future wireless
technology. EBG offers the potential for novel and unique capabilities to manipulate electromagnetic waves. In this paper,
Multisize EBG structures were investigated. Studies were carried with the goal to explore the possibility of achieving a wide
stopband region by employing a multisize arrangement. Investigations were carried for four types of shapes including Circular,
Square, Koch-square and Fractal-minkowski. Promising results show that multisize EBG design with equal edge gap offers a
wide stopband region with deep attenuation, while sustaining the compact size. Arrangement of the multisize EBG patch is a
significant factor in achieving the desired wide stopband as well as the patch’s and via’s size.
Index Terms— Band Stop EBG, EBG, EBG for antenna, Multisize EBG, Wide Stopband
—————————— ——————————
1 INTRODUCTION
I
N recent years, Electromagnetic Band Gap (EBG) structures have attracted many microwave circuits and antenna researchers as the new focus area of interest. EBG
consists of a plane with metallic patches in periodic arrangement. Figure 1 illustrates the basic mushroom-like
EBG structure. The structure contains periodic metal
patches that are connected to ground with vias. Such EBG
acts as a two-dimensional band-stop filter which can
block electromagnetic wave propagation within certain
desired frequencies [1-2].
EBG structure can be applied widely in improving microwave applications’ performance since it offers unique
properties such as wideband rejection for millimeter and
microwave range [3].
Wide rejection bandwidth is typically achieved by increasing the dimension or the number of patches which
results bigger physical size.
In this study, multisize circular patch EBG structure is
proposed to achieve a wide bandstop with high attenuation to maintain a compact structure.
EBG structure can be described as a lumped circuit [4]
that depicts an electric filter that consists of parallel capacitor and inductor (Figure 1). The patch width and gap
represent the capacitance’s characteristic while the inductance effect is associated with the vias’ dimensions.
The centre stopband frequency of an EBG structure can
be determined from the following formulae in (1) [5]. C
indicates the capacitance while L denotes the inductance
effect. On the other hand, the bandwidth of the stopband
frequency can be deduced from Equation in (2), where is
the free space impedance [6].
fc =
1
2π LC
1
BW =
η
L
C
(1)
(2)
To date, there is no accurate close form equation that
can analytically determine the stopband frequency for a
specific EBG structure. The equations presented earlier
————————————————
will serve as a starting point in designing the desired EBG
• K. Kamardin is withFaculty of Electrical Engineering, Universiti Teknologi structure.
Malaysia, 81310 Skudai, Johor Bahru.
Help from Finite Different Time Domain (FDTD) cal• M. K. A. Rahim is withFaculty of Electrical Engineering, Universiti Tekculation
is needed to complete the analysis. In this study,
nologi Malaysia, 81310 Skudai, Johor Bahru.
• N.A.Samsuri and M. A. R. osman are withFaculty of Electrical Engineer- the design will be solved using CST simulation software
ing, Universiti Teknologi Malaysia, 81310 Skudai, Johor Bahru.
that utilises FDTD simulation.
Fig. 1. Mushroom EBG layout and Equivalent Lumped Circuit [5]
© 2010 JOT
http://sites.google.com/site/journaloftelecommunications/
JOURNAL OF TELECOMMUNICATIONS, VOLUME 6, ISSUE 1, DECEMBER 2010
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2 SINGLE PERIOD AND MULTISIZE EBG
STRUCTURES
This study was carried with the goal to explore the possibility of achieving a wide stopband region by employing
a multisize arrangement. It is predicted that an optimum
multisize EBG structure design can establish an ultra
Fig. 2. Simulation set-up based on method of suspended transmission line
wide stopband region due to the cascading of individuals’ stopband of different patch size.
The investigation starts from single period EBG pattern before extending to multisize arrangement. Arrangement of the multize structures was investigated by
comparing structures with equal edge gap between
patches; and structures with equal centre spacing between patches.
Method of suspended transmission line (MOSTL) was
used to determine the S21 value to analyse the stopband
region. Transmission line of 3mm width is proposed to be
placed on top of a dielectric board (Figure 2). Such line
matches well with 50 ohm SMA connector.
The material used for the EBG structure is a 1.6mm
thick FR4 board with relative permittivity of 4.5 and tangent loss of 0.019. The design and analysis was conducted
using CST software that applies Finite Different Time
Domain (FDTD).
Four types of EBG shapes were used in this study,
which are circular, square, koch-square and fractalminkowski shapes.
(a)
(a)
(b)
(b)
(c)
(c)
Fig. 3. Schematic representation of Circular EBG (a) Single Period
(b) Multisize EBG with equal edge gap (c) Multisize EBG with equal
centre spacing distance
(i)
(ii)
Fig. 4. Schematic representation of square, koch-square, fractalminkowski (i) Single Period (ii) Multisize EBG with equal edge
gap
JOURNAL OF TELECOMMUNICATIONS, VOLUME 6, ISSUE 1, DECEMBER 2010
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Figure 3 (a) illustrates the schematic representation of
single period Circular EBG structures with 30 elements of
50x50mm dimension. The EBG structure in this study
consists of periodic circular patches grounded with vias.
The patch are separated with a gap, g. The radius, r of the
patch is 3mm and via radius is 0.5mm.
Comparison was conducted between single period
structure (Figure 3(a)) and multisize structure (Figure 3(b,
c)). Arrangement of the multisize structures was also investigated by comparing multisize design with equal
edge gap (30 elements, edge gap= 3mm) (Figure 3(b)),
with multisize structure with equal centre spacing (25
elements, centre spacing = 10mm) design (Figure 3(c)).
Following the previous investigation, the study was
extended to explore the square, koch-square and fractalminkowski shape arrangements with similar approach
(Figure 4).
(a) Circular
3 RESULTS AND DISCUSSION
The EBG structures of single and multisize arrangements
have been simulated using method of suspended microstrip line. When a multisize arrangement was proposed, a
significant wide bandstop has been established. Comparison between multisize with equal edge gap; versus multisize with equal centre spacing was observed for circular
EBG structure, as an initial investigation.
From the results (Figure 5), multisize structure with
equal edge gap shows a wider stopband region with
bandwidth of 5.79GHz (3.05-8.84GHz) compared to the
multisize structure with equal centre spacing with bandwidth equals to 3.79GHz (3.04-6.83GHz).
(b) Square
(c) Koch-square
Fig. 5. Simulated transmission coefficient S21 for Multisize Circular
EBG with equal edge gap versus equal centre spacing distance
The investigation was then continued to analyse the
results between single period and multisize structure
with equal edge gap arrangement. Figure 6 shows S21
results for single and multisize EBG structures for four
different shapes which include circular, square, kochsquare and fractal-minkowski EBG structures.
Referring to Figure 6 (a), multisize arrangement for
circular patch EBG, shows a huge improvement on the
stopband region with bandwidth of 5.79GHz (3.05–
8.84GHz), compared with the single period of bandwidth
equals to 2.67GHz (3.38-6.05GHz). A very deep attenuation can also be observed.
(d) Fractal-minkowski
Fig. 6. S21 for single and multisize EBG with equal edge gap for
four different shapes
Multisize arrangement of square shapes improvised
the stopband bandwidth from 2.8-8.03 GHz, a 55.8% improvement from the single arrangement as shown in Figure 6 (b).
JOURNAL OF TELECOMMUNICATIONS, VOLUME 6, ISSUE 1, DECEMBER 2010
TABLE 1
BANDGAP FREQUENCIES AND BANDWIDTH BETWEEN SINGLE PERIOD AND MULTISIZE ARRANGEMENT FOR CIRCULAR, SQUARE,
KOCH-SQUARE AND FRACTAL-MINKOWSKI EBG STRUCTURES
Single Period
Type of
EBG
structure
Fig. 7. Fabricated Multisize Circular Patch EBG
Multisize Circular Patch EBG
Simulation vs Measurement
Bandgap
frequencies
(GHz)
Circular
3.38 – 6.05
Square
3.11 - 5.33
Kochsquare
3.59 – 6.47
Fractalminkowski
3.39 – 5.53
9.67 – 10.33
Multisize
Band
width
(%)
59
54.5
59.8
49.4
Bandwidth
Enhance
-ment
(%)
Bandgap
frequencies
(GHz)
Bandwidth
(%)
3.05 –
8.84
2.8 - 8.03
111.5
52.5
110.3
119.1
55.8
59.3
117.5
68.1
3.36– 10.4
3.01– 9.19
17.14 –
19.25
0
S21 (dB)
-20
-40
-60
-80
Measurement
Simulation
-100
2
4
6
8
10
Frequency (GHz)
Fig. 8. Measurement versus Simulation of S21 Multisize Circular
Patch EBG
Similar trend was also obtained for koch-square ebg
structure with stopband region from 3.36-10.4GHz for
multisize arrangement; an improvement from 3.596.47GHz of the single period design (Figure 6 (c)).
As for fractal-minkowski EBG, the single period arrangement exhibits a dual narrow stopbands at 3.39 – 5.53
GHz and 9.67 – 10.33 GHz (Figure 6 (d)). As expected,
due to the nature of fractal-minkowski shape, multibands
are exhibited by fractal structure.
When a multisize arrangement was deployed, dual
bands were obtained with an ultra wide first stopband at
3.01 – 9.19 GHz and the second band from 17.14 – 19.25
GHz. In parallel with multibands characteristics of fractal
shape, wider stopbands region was also observed with
multisize arrangement as opposed to the typical narrowbands.
Measurement was then conducted to validate the simulation results (Figure 7). Figure 8 show the comparison
between measurement and simulation of the Multisize
Circular with Equal Edge gap EBG arrangement. From
the graph, similar trend between measurement and simulation can be seen. Measurement results shows a
bandstop region from 3.4-12.83 GHz while 3.1-6.04GHz
for simulation.
The frequency shift is predicted due to the dielectric
loss of the FR4 material used as well as the inconsistency
of dielectric constant value of such material for different
frequencies. Despite the small shift, the wide stopband
trend is obtained hence validating the simulations results.
Table 1 summarizes the comparison between single period and multisize structure for all circular, square, kochsquare and fractal-minkowski shapes. Promising simulation and measurement results show that multisize EBG
design with equal edge gap offers a wide stopband region
with deep attenuation, while sustaining the compact size.
The bandwidths have been improved to more than 50%
when multisize arrangements were deployed for all
shapes.
4 CONCLUSION
In this study, the possibility of multisize EBG structure to achieve a wide stopband region was investigated for four types of shapes i.e. circular, square,
koch-square and fractal-minkowski. Promising results
show that multisize design with equal edge gap EBG
structure exhibits a stopband with high attenuation,
while maintaining a compact physical size.
The patch parameters including the width or radius;
and the gap between the elements plays important
roles as they denotes the L and C values that determine the operating frequencies of the structures. Arrangement of the EBG patch is also an important factor
to obtain a broad stopband region in the multisize EBG
structure. It is predicted that an optimum multisize
EBG structure design can establish an ultra wide stopband region due to the cascading of individuals’ stopband of different patch size.
Such design can be utilised as a bandstop filter that
can be integrated in many applications such as compact high performance antennas. In addition, the
bandstop property can also be applied as a band rejecter in antenna system. This new application of EBG is
appealing in antenna designs especially as a tunable
band rejecter.
25
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ACKNOWLEDGMENT
The authors wish to thank the Ministry of Science Technology and Innovation (MOSTI) and Ministry of Higher
Education (MOHE) Malaysia for supporting the research
work.
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
M. Rahaman and M. Stuchly, ‘Wide-band microstrip patch antenna
with planar PBG structure’, in Proc. IEEE Con. on AP-S Dig..,vol. 2, July
2001, pp. 486-489
S. Sharma and L. Shafai, ‘Enhanced performance of an apeture-coupled
rectangular microstrip antenna on a simplified unipolar compact photonic bandgap (UCPBG) structure,’ in Proc. IEEE AP-S Dig., vol. 2, July
2001, pp. 498-501
S. Y. Huang, Y. H. Lee, ‘A Novel Dual-Plane Compact Electromagnetic
Band-Gap (DPC-EBG) Filter Design’, 4th International Conference on
Microwave and Millimeter Wave Technology Proceedings, 2004
E. Yablonovitch, et al, ‘High-imepdance Electromagnetic Surfaces with
a Forbidden Frequency Band’, IEEE Trans. On Microw.Theo. and
Tech., Nov. 1999, Vol. 47, No. 11, pp. 2059-2074
F. Yang and Y. R. Samii, “Microstrip antennas integrated with EBG
structures: a low mutual coupling design for array app.”, IEEE Trans.
Ant. and Prop., vol. 51, pp. 2936-2946, Oct. 2003.
L. Yang, et al, ‘A Spiral EBG structure and its application in Microstrip
Antenna Array’, APMC2005, December 2005, Vol. 13, pp. 4
K. Kamardin received her B.Eng. in Electronic (Communications)
from University of Sheffield, United Kingdom in 2004 and obtained
her MSc from Universiti Teknologi Mara (UiTM) in 2007. She had
previously served as a Senior Assistant Researcher in TM Research
& Development for three years. Currently, she is pursuing her PhD in
Electrical Engineering at the Faculty of Electrical Engineering, Universiti Teknologi Malaysia. Her research interests are in the area of
Antenna & Propagation and Metamaterials Enginering. She is focusing in the field of Electromagnetic Band Gap Structure for Antenna
Engineering.
M. K. A. Rahim received his B.Eng. in Electrical and Electronics
from University of Strathclyde U.K. in 1987, Master in Electrical
Communication Engineering from University of New South Wales
Australia in 1992 and PhD in Electrical Engineering from University
of Brimingham U.K. in 2003. Currently, he is an Associate Professor
at the Faculty of Electrical Engineering, Universiti Teknologi Malaysia, Skudai, 81310, Johor, Malaysia. His current research interests
are in the area of Planar and Dielectric antenna, Active Antenna,
Array antenna, Electromagnetic bad gap, (EBG), Left handed metamaterial (LHM), Frequency Selective Surface (FSS) Artificial magnetic conductor (AMC).
N. A. Samsuri received her B.Eng. in Electrical Engineering (Telecommunication) for Universiti Teknologi Malaysia in 2001. She obtained her MSc and PhD from Loughborough Univeristy, United
Kindgom in 2004 and 2009 respectively. She is currently serve as a
lecturer in Faculty of Electrical Engineering, Universiti Teknologi
Malaysia.
M. A. R. Osman received her B.Sc. in Electronic Engineering from
Sudan University of Science and Technology, Khartoum, Sudan in
2002 and MEng in Electrical (Electronics & Telecommunication) from
Universiti Teknologi Malaysia in 2007. Currently, she is pursuing her
PhD in Electrical Engineering at the Faculty of Electrical Engineering, Universiti Teknologi Malaysia. Her current research interest is in
the area of Antennas and Propagations Systems. More focus is on
the antenna designs and performances for wearable applications.