2014 International Conference on Electronics and Communication System (lCECS -2014)
Design of Modified Sierpinski Antenna for WLAN Applications PSR Chowdary
A.Mallikarjuna Prasad
P.Mallikarjuna Rao
Department ofElectronics & Communication Engineering Raghu Institute of Technology Visakhapatnam, India
Department ofElectronics & Communication Engineering University College ofEngineering, JNTUK Kakinada, India
Department ofElectronics & Communication Engineering AU College ofEngineering (AJ, Andhra University Visakhapatnam, India
psr
[email protected] _
Abstract-The application
Sierpinski
in
(SPK)
multiband
geometry
antennas.
has
The
a
paramount
multifrequency
characteristics of the SPK are characterized by its scaling factor and successive iterations. To allocate more number of bands the geometry has to undergo more number of iterations which makes the antenna more complicated for fabrication. In this work we propose modifications to the SPK geometry with the ability of
allocating two frequencies close to WLAN applications. The
independent
radiating
elements
for
several
wireless
and
mobile communications took initiation. Much new geometry has
been
derived
from
Mandelbrot's
"Concept
of New
Geometry" [4]. Some of them are so popular in serving as radiating elements. Among those,
Sierpinski triangle and
Sierpinski carpet are named after Sierpinski (191 6), Hilbert curves named after Hilbert.D (1891), Koch curves named after
designed antenna preserved its multiple frequency characteristics
Koch.V.H (1904), Julian structures named after Julia.G (1918)
and are verified with the radiation plots.
and Contor shapes named after Contor.G (1872) have wide applications
Keywords-Sierpinski; multiband; WLAN;
I.
INTRODUCTION
B.
A. Concept ofFractal Geometry The word antenna is often prefixed with the word latest which gives the state of research in the field. In the latest antenna research the fractal geometry took a vital role. It is a powerful means of describing any geometrical shapes. The shapes of Coast line, leaf, clouds etc. are some complex phenomenon that are described effectively using fractals [1]. This magnificent strategy has drawn the attention of many elites from mathematics, computer science, statistics, image and signal processing and electromagnetic group.
Since the
breakthrough of personal communication systems, wireless and mobile devices, the demand for efficient wideband and multi band radiating systems has increased enormously. Being frequency independent certainly
considered
as
the
basic
characterization but not the only criterion for an antenna to be multiband, provided the element shows similar impedance and radiation
patterns
Considering
the
at
several
applications
resonating
of
in
electromagnetics
with
their
vital
electrodynamics.
frequencies.
multiband
in
wireless
SelfSimilarity and Frequency Independent Features of Fractals
Self-similarity and the recursive structure of the fractals have drawn the attention of Electromagnetic Engineers [5-10]. The frequency independent characteristics of an element are due to the
ability
the
shape
for
many
iterations
or
periodic and Spiral were proposed [12] and proved to have constant
impedance
characteristics.
Rumsey
V.H,
in
his
conclusive literature about frequency independent antennas proposed a new way of defming an antenna and stated that "If the antenna dimensions are mentioned only in terms of angles then
the
radiation
patterns
and
impedance
pattern
characteristics of that antenna are frequency independent". Multiresonant characteristics of the Koch curves have been described
in
[13-17].
The
new
era
of
reconfigurable
characteristics of fractal antennas have been experimentally verified using micromachining [18].
communications and the environment like handheld radio
II.
SIERPINSKI GEOMETRY
An SPK has various flavors of construction. These
ease of installation and also required to maintain low profile. the radiating
retain
similar, self-complimentary and recursive structures like Log
devices, the antenna has to be compact in size so as to give the Targeting high directivity and miniaturization,
to
transformations [11]. But even before the Mandelbrot self
variations are observed with respect to the point of view,
element took many changes in its geometry [2-3]. The process
rotation and scaling. The muItiband behavior of the fractal
of proposing new geometries is a continuous phenomenon.
shaped SPK is described in [19] and further a comparative
Since
study
the
geometries,
advent the
of
idea
Mandelbrot,
the
of
fractals
utilizing
father as
of
fractal
frequency
between the
SPK
monopole and dipole is also
2014 International Conference on Electronics and Communication System (lCECS -2014) presented in it. The resultant log periodic behavior of the
Where
SPK is due to the self similarity property of it. A.
x
=
{o
'
k= O
1, k > 1
Effective area considerations in SPK The
Sierpinski
(SPK)
geometry
exists
in
two
different forms namely SPK triangle and SPK carpet. The basic structure of SPK is derived from a triangle patch and runs
through
several
iterations
to
show
multiband
characteristics. For each iteration the circumference and the whole size varies. If a triangle of unit area is considered then after the first iteration 114 of the area is removed. Consequently after the second and third iteration, 311 6 and 9/64 of the area is removed respectively as shown in the figure (1). The generalized expression for this phenomenon is given by
5 =scale factor of the geometry,
p
=
� 0.230735 -
N
AN
=
III.
1 / 32: (3 / 4 Y i=l
¢ =� 5
MODIFIED SPK GEOMETRY
A triangular patch antenna wi II observe a decrease in the surface area when obtained from a rectangular patch which
(2)
results in incremented resonating frequency. Also
it
has
where AN refers to the area removed. From the above
proven to resonate at multiple frequencies though it has
equation it can be inferred that after infinite iterations
indefinite peaks in the radiation pattern. Considering the SPK,
A 0
previous
iteration SPK to a scaled down version and adjusting it in the
(b)
2014 International Conference on Electronics and Communication System (lCECS -2014)
o
. jal2 (c) -90
f--+--k---j--+--+�· :c--+--+--+-.J·---I-
(d)
-180
(c)
Fig. 2. Transfonnation of modified SPK from a rectangular patch. IV.
IS.SS
SIMULATION RESULTS
resonant frequency 2.45GHz. Accordingly the height of the antenna is considered as a=18.2mm. Whereas the height of the triangle in Fig.2(d) will have al=12mm to facilitate the transformation. The simulation is carried on HFSS. The thickness of the substrate is chosen as 1.52 mm with £r=3.2 and loss tangent of 0.0027. Various
reports
like reflection
coefficient
---:::--
--
--{----;;;;;, ;;;-
---:.._
------------
------------
8.ee
The perimeter of the triangle should be chosen such that it is slightly greater than the half wave length of the first
,--
: 6.ee m "
E�
4.6£1 2.08
0 . e""' -;5 eo.�---:6" e --�;---�o;;;--l-'--;-,;;;---'. o""' o.eo '1� Frequency [GHzJ
� __-;-:;;!--'-'--;;-�_';;:_\;;;_'-L
(d)
curve,
Radiation pattern, VSWR curves and Directivity plots are taken using the HFSS tool as shown in the Fig 3(a)-(d). These plots are useful in understanding the behavior of the modified geometry before going for fabrication.
... uOO ���-----,
(e) Fig.3. (a) Reflection Coefficient plot (b) Radiation Characteristics at 2.68 GHz (c) Radiation Characteristics at 5.3 GHz (d) Frequency vs Directivity plot. (e) VSWR plot �
OO
�
�IGHzl
moo �
l .OO��2�OO--�100�--4 � .OO��&OO=---��oo� �OO��5 �OO . ---=nOO�� 7
(a)
From
Fig.3(a)
the
reflection
coefficient
characteristics curve it can be understood that the modified geometry resonates at multiple frequencies. Only those dips with reflection coefficient less than -lOdB are considered. The first two dips are observed at 2. 68 GHz and 5.34 GHz. The radiation characteristics plots at 2.68 GHz and 5.34 GHz are taken to confirm that they are resonating frequencies as shown in the Fig.3(b)&(c). The plots do confirm the same as they are in agreement with the pattern of patch antenna with main lobe on upper region and no lobe on the lower region. From the Directivity plot as shown in the Fig.3(d) it can be inferred that the Directivity takes a maximum value of 10dB at first resonating frequency and further takes respectable values at all
·180
(b)
the resonating frequencies.
2014 International Conference on Electronics and Communication System (lCECS -2014) V.
CONCLUSIONS
The proposed geometry is simulated using HFSS and resonant
frequencies
are
identified
from
the
reflection
coefficient graphs and are verified with the corresponding radiation pattern and VSWR plots. A considerable directivity can be read from the directivity plot. The dimension of the smallest triangle in the Sierpinski triangle in its 2nd iteration is enhanced which may decrease some complexities involved in fabrication.
The
miniaturization
and
the
multifrequency
characteristics of the basic geometry are found to be unaltered with these modifications.
ACKNOWLEDGMENT The fust author acknowledges the support from sri Raghu Kalidindi,
chairman,
Raghu
Educational
Institutions,
Visakhapatnam.
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[3]
[4] [5]
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[12] Mushiake, Y., "Self-complementary antennas," Antennas and Propagation Magazine,IEEE ,vol.34,no.6,pp.23,29,Dec. 1992. [13] K.J. Vinoy, K.A. Jose and V.K. Varadan, "Generalized design of multi resonant dipole antennas using Koch curves," Applied Computational Electromagnetics Society Journal. pp. 22-31,vol 19,no. Ia,2004. [14] E. Rufus ,Z. C. Alex and P. V. Chaitanya "A modified bow-tie antenna for microwave imaging applications ", J. MicrolV., Optoelectron., Electromagn. App/icat., vol. 7, no. 2, pp.115 -122 2008.
[15] R. S. Aziz, M. A S. Alkanhal, and A-F. Sheta, "Multiband fractal-like antennas," Progress in Electromagnetics Research 8, Vol. 29, 339-354, 2011. [16] Lizzi, L. and G. Oliveri, "Hybrid design of a fractal-shaped GSMlUMTS antenna," Journal oj Electromagnetic Waves and Application, Vol. 24,No. 5--6,707-719,2011. [17] Liu, W. c., P.-W. Chen, and C. C. Liu, "Triple-band planar monopole antenna for DMB/WLAN applications," Journal oj Electromagnetic Waves and Application, Vol. 24,No. 5--6,653-661,2011. [18] K.J. Vinoy and V.K. Varadan, "Design of reconfigurable fractal antennas and RF-MEMS for space-based systems," Smart Materials and Structures, vol. 10,pp. 1211-1223,2001. [19] c. Puente , J. Romeu ,R. Pous and A Cardama "On the behavior of the sierpinski multiband fractal antenna ", iEEE Trans. Antennas Propag, vol. 46, no. 4, pp.517 -524 1998. [20] Mishra,R.K.; Ghatak,R.; Poddar, D.R., "Design Formula for Sierpinski Gasket Pre-Fractal Planar-Monopole Antennas [Antenna Designer's Notebook]," Antennas and Propagation Magazine, IEEE , vo1.50, no.3, pp.I04,I07,June 2008. [21] Tsachtsiris,G.F.; Soras,C.F.; Karaboikis,M.P.; Makios,V.T., "Analysis of a modified Sierpinski gasket monopole antenna printed on dual band wireless devices," Antennas and Propagation, iEEE Transactions on , vo1.52,no.IO,pp.2571,2579,Oct. 2004.
Authors
P Satish Rama Chowdary received M.Tech in Radar and Microwave Engg from Andhra University in the year 2009. He is currently pursuing PhD in Department of Electronics & Communication Engg, JNTUK, Kakinada, AP. He is working in the Department of ECE, Raghu Institute of Technology, Visakhapatnam, AP. His area of interest includes Computational Electromagnetics and Antennas. He is a Life Member of Institute of Electronics and Telecommunication Engineers (IETE),and Instrument Society of India(ISI). A.Mallikarjuna Prasad did his B.Tech in ECE from Nagarjuna University, during 1984-88. He did his M.Tech in Electronics&lnstrumetation from Andhra University in 1992 and completed his Ph.D in 2009 from JNTU in the field of Antennas. He has joined JNT University service as Associate Professor of ECE in June 2003. He got promoted as Professor in ECE during Nov 2011. He has 20 publications in various International and National Journals and conferences. His areas of interest includes Antennas and Bio Medical Instrumentation. He is a Life Member of Society of EMC Engineers (India), Indian Society for Technical Education (ISTE), Intitute of Electronics and Telecommunication Engineers (IETE), and Instrument Society of India(ISI). He won best teacher award by student evaluation of 2008 batch.
P. Mallikarjuna Rao, received B.E, M.E and PhD degrees from Andhra University, Visakhapatnam. He is a recipient of Best PhD Award during 1999. He joined as Assistant Professor in the Department of ECE, Andhra University in 1990 and became Associate Professor in 1994 and Professor in 2002. He is Chairman, Board of Studies, ECE, Andhra University. Prior to this he served as Assistant Professor in SRKR College of Engineering,Bheemavaram during 1985-90. His areas of interest includes Antennas and Bio Medical Signal Processing. He has 19 International Journal publications and 31 International and National Conferences papers. Prof P. Mallikarjuna.Rao is a fellow of Intitute of Electronics and Telecommunication Engineers (IETE). He is a Life Member of Society of EMC Engineers (India) and Indian Society for Technical Education (ISTE)
