=4.3) with different configurations of ground planes at the bottom of the substrate. The proposed antenna (without ground) offers excellent ultra wideband performance ranging from 3.80International Journal of Scientific & Engineering Research, Volume 4, Issue 7, July-2013 1203
ISSN 2229-5518
Design of Circular with triangle Microstrip Fractal
Antenna for Dual band and UWB applications
B. Rama Rao1 S.Alekhya2 Dr. P.V. Sridevi3
Abstract—This paper presents the design of crown circular shaped Fractal Microstrip patch antenna for dual band and ultra-wideband (UWB) applications. The two iterative Circular fractal antenna have been designed and fabricated on FR4 substrate ( =4.3) with different configurations of ground planes at the bottom of the substrate. The proposed antenna (without ground) offers excellent ultra wideband performance ranging from 3.80
GHz to 12.8 GHz. The antenna exhibits bandwidth of 9 GHz. The experimental radiation pattern of fractal antenna has been observed nearly Omni- directional. Such type of antenna can be used for UWB system.
Index Terms- Microstrip patch antenna, Fractal antenna, ultra-wideband, bandwidth, crown.
In modern communication world microstrip patch antenna is basic and widely used antenna in mobile, avionics, radar applications as it is low profile antenna and can be integrated easily with other RF front-end circuits. However low bandwidth is major drawback of microstrip patch antenna. To overcome this, dual band, multi band and ultra wide band (UWB) are being designed by changing parameters (shapes) of basic antenna.
As the performances of microstrip patch antenna with
basic geometric shapes have been studied during 19th century, fractal antennas have drawn special interest in microwave engineering since a century. “A fractal is a rough or fragmented geometric shape that can be split into parts, each of which is a reduced-size copy of the whole." The term is coined by Benoît Mandelbrot in 1975 and was derived from the Latin word fractus, meaning "broken" or "fractured."[1] There various types of fractal antennas includes (1) the von Koch curve, (2) the Sierpinski (gasket and carpet) and (3) the fractal tree. The proposed
antenna structure comes under Sierpinski Gasket as its structure is repeated again and again [7][6].
• B. Rama Rao is with Associate Professor, Department of Electronics and Communication Engineering, Aditya Institute of Technology and Management, Tekkali. AP., INDIA. (e-mail: ramu_sri07@rediffmail.com ).
• S.Alekhya is student of M.Tech in AITAM.
In 2002 bandwidth of ultra-wideband (UWB) radio system approved by Federal Communications Commission is 3-
10.8 GHz [2].Fractal geometries have two common
properties, space-filling and self-similarity [5][1]. It is self similar in a way that structure of antenna is repeated indefinite form so as to produce similar surface current distributions for different frequencies, i.e. to produce multiband response. The space filling property leads to an increase of the electrical length and hence the physical size of the whole structure can be reduced.
Fig 1. a) Fabricated UWB crown fractal antenna
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International Journal of Scientific & Engineering Research, Volume 4, Issue 7, July-2013 1204
ISSN 2229-5518
(a)
Fig1.b) UWB fractal antenna design during simulation on
HFSS 13.0
The antenna is built over a 100x106 mm FR4 substrate with dielectric constant (
) 4.3, thickness 1.6 mm. The upper plane (radiating element) is an equilateral triangular slot of side 71.016 mm on solid circle of 82 mm diameter, by repeated stages of subtracting triangles with sides half the size of the former triangles from corresponding circles with diameter half of their former retaining their centre of geometry the proposed antenna is generated at the fourth stage. The feed of antenna is 2.2 mm wide and 15 mm long. The space between ground and feed is 0.25 mm.
The advantage of CPW fed is that both radiating
element and ground plane is on the same side of path[3][1].
However to achieve dual band response through this design ground plane is also placed on the bottom of the patch of size 50x53 mm (half the size of substrate).
As the shape antenna is fractal triangular slot over circle it
is named as crown circular microstrip fractal antenna in the
literature [6]. Basically it is designed for UWB applications, but our analysis reports the performance of this UWB antenna into dual band antenna by placing a shorted half ground plane on the bottom of the substrate which was absent on actual crown circular microstrip fractal antenna design[7].
(b) (c)
Fig2. (a) Front view of dual band and UWB antenna. (b)back view of dual band antenna.
(c) Back view of UWB antenna (no ground)
Table 1: Values of various Parameters used for the design.
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International Journal of Scientific & Engineering Research, Volume 4, Issue 7, July-2013 1205
ISSN 2229-5518
The design expression of simple circular microstrip antenna for calculating the resonant frequency is given as [4]
The performance of fabricated antenna is tested using 2- port vector network analyzer, Agilent E507C1. The fig 3 shows the experimental setup used to measure return loss,
VSWR and smith chart etc through network analyzer.
f r =
1.841vo
2Πreff
∈eff
(1)
Where vo is the velocity of light. The effective radius reff can
be calculated by following expression [4]
Fig.3 experimental setup for measuring parameters of a
h
r
microstrip patch antenna
reff
= ro
1 +
2 ln o +
Πro ∈eff
h
2h
1 / 2
The simulated and practically tested results of crown antenna with no ground plane at the bottom are compared in fig 4.(a). The antenna resonates for the entire band of 3.8-
(1.41∈r
+1.77)+
(0.268 ∈
ro
+1.65)
(2)
12.5 GHz covering entire commercial UWB band approved by FCC.
Simulation of both the designs is done over High Frequency Structure Simulator (HFSS) version 13. The simulated results for various parameters like return loss, radiation pattern, gain etc., have been obtained from this software. Table 5.2 shows the various parameters used in the designing of dual band fractal circular patch antenna.
The most serious problem for UWB application is interference. Rejection of interference is necessary for UWB applications with existing wireless technologies such as IEEE 802.11a in USA (5.15-5.35 GHz, 5.725-5.825 GHz) [4]. A band stop filter can be used but the use of filter would make the system complex. Many UWB antennas have been designed to overcome this interference problem. However for better selectivity of frequency of operation, antennas with narrow bandwidth are used. Here comes the importance of antenna radiating only for certain frequencies like dual band and triple band antenna. Both the antennas, UWB and dual band antennas are fabricated using etching process and 50Ω ports are soldered at the end of the feed point.
Measured result simulated result
Fig 4.(a) Measured and simulated return loss curves of crown antenna without ground
The crown antenna with half ground at the bottom resonates at two frequencies 3, 3.9 GHz as shown in fig 4(b). Thus, it can be used for dual band applications.
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International Journal of Scientific & Engineering Research, Volume 4, Issue 7, July-2013 1206
ISSN 2229-5518
Measured result simulated result
Fig 4.(b) Measured and simulated return loss curves of crown antenna with half ground at the bottom
Fig 4.(c) VSWR curve of antenna with half ground measured By Vector network Analyzer
Fig 4.(d) VSWR curve for UWB antenna measured By
Vector network Analyzer
<2 which covers the commercial UWB band approved by the FCC . bandwidth of antenna-12 is from 2.2 to 12GHz,. Radiation patterns of these antennas are Omni-directional
in the H-plane and bidirectional in E-plane. These properties of the antennas make it a suitable candidate for modern UWB applications. These antennas are compact, light weight, low cost, simple to fabrication and easy to integrate with MIC/MMIC devices. This antenna may be useful in applications like precision positioning systems, ground penetrating radar and vehicular radar and medical imaging assuming all environmental conditions are standard.
[1] M. Ding and R. Jin, “Design of cpw-fed ultra wideband fractral antenna,” Microwave and Optical Technology Letters, vol. 49, pp. 173–176, Jan.2007.
[2] First Report and Order (FCC 02-48). Action by the
Commission February 14, 2002. New Public Safety
Applications and Broadband internet access among uses envisioned by FCC authorization of Ultra-Wideband Technology
[3] Liang J, Guo L, Chiau CC. CPW-fed circular disc
monopole antenna for UWB application, IEEE
International Workshop on Antenna and Technology: Small Antennas and Novel Metamaterials, Marina Mandarin, Singapore, March 7–9, 2005; 505–508.
[4] Eng Gee Lim, Zhao Wang, Chi-Un Lei, Yuanzhe
Wang, K.L. Man “Ultra Wideband Antennas – Past and Present” IAENG International Journal of Computer Science, 37:3, IJCS_37_3_12
[5] Ray KP (2008) Design aspects of printed
monopole antennas for ultra-wide band
applications. Intl. J. Antennas & Propag. Article ID
713858.
[6] MURTAZA, N., HEIN, M. A. Folded Sierpinski monopole antenna with self-similar radiation properties. In Proceeding of the 3rd European Wireless Technology Conference. September 2010,p. 189 - 192.
[7] Dehkhoda P, Avakoli A. A crown square
microstrip fractal antenna. IEEE Antennas Propag
Soc Int Symp Dig 2004; 3: 2396 –2399.
Fractal antennas with CPW-fed offer larger bandwidth has been investigated. The simulated bandwidth of the
proposed antenna-1 is from 2.5 to 11GHz (113%) for VSWR
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