COMPOSITE STRUCTURE FRACTAL WIDEBAND MONOPOLE ANTENNA FOR ISM BAND APPLICATIONS

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1 COMPOSITE STRUCTURE FRACTAL WIDEBAND MONOPOLE ANTENNA FOR ISM BAND APPLICATIONS Suraj A. Shete 1, Girish G. Bhide 2, Sandeep R. Nalage 3 and Ashish B.Vartak 4 1,2,3,4 Assistant Professor, FAMT Ratnagiri Abstract The fractal antennas possess the property of self-similarity, which plays a significant role to create a fractal circular monopole patch antenna. The other important property is that, Space-filling which serves the purpose of antenna size reduction. Further utility of fractal geometry for antenna fabrication adds more electrical length in less space. These two properties facilitate us variety of applications to be derived from fractal antennas. The Co-planar waveguide (CPW) feed type improves the antenna bandwidth. In this work proposed antenna is design and fabricated on FR-4 Material (ε r = 4.4).This antenna design can efficiently supports Industrial Scientific- Medical (ISM) band. Keywords - Industrial Scientific- Medical (ISM) band,co-planar waveguide feed, Fractal geometry, Monopole antenna. I. INTRODUCTION With frequency spectrum crowding and emerging wideband systems being deployed, there is demand for wideband antennas [1]. Different techniques have been utilized to implement the wideband antennas. These methodologies include use of CPW Feed for design of wideband antenna [2].Latest trends in communication system design need broad band antennas with miniaturized dimensions [3,4]. With the advances in Mobile communication systems and associated applications, wideband antennas with variety of geometries and variability of designs become a great demand. In this regard, there various types of fractal antennas include [2,5] von Koch curve fractal tree Sierpinski (gasket and carpet) Apollonius circle and so on II.RELATED WORK 2.1 Sierpinski Configuration Waclaw Sierpinski, a Polish mathematician came up with a new fractal configuration in 1916, there onward commonly referred in his honor [6]. Due to self-similarity principle followed by Sierpinski configuration a monopole antenna designed using it shows the wideband behavior in excellent manner. For generation of such a fractal geometry, the four steps of conventional Sierpinski triangle iterations, are employed as shown in Fig.1The central triangles are eliminated from the antenna, giving three(first step) or nine (second step) equilateral triangles, which are having 50% or 33% height in comparison with the original triangle.from perspective of understanding of radiating systems, Fig. can be interpreted as the dark triangular areas representing a conducting material, while the white triangular areas symbolize non-metallic regions. This configuration, with a fractal dimension of approximately 1.58=(log 3/log 2), is commonly used by scholars as a fundamental fractal antennas design [7], [8]. The Sierpinski gasket fractal antenna is completely described in terms of four parameters, namely, the triangle height(h t ), the flare angle (α t ), the iteration number (n), and the scaling factor(ψ). As was described in [9], the Sierpinski monopole presents a log-periodic behavior. DOI: /IJMTER SDIDG 275

2 Figure 1 Sierpinski Triangular Fractal Geometries 2.2 APOLLONIUS FRACTAL CONFIGURATION The Greek mathematician Apollonius put forth new fractal geometry in the form of Apollonius circles arranged in tangential manner to one another. For the generation of this configuration steps mentioned below needs to be followed- 1. Initially, begin with three circles of any size, each of which is tangential to the others ( for example circles C1,C2,C3 from fig.2 ). 2. As per the view of Apollonius, two other circles also exist which do not intersect, possessing the characteristics of being tangential to the original 3 circles ( for example circles C4 and C5 from fig.2 ). These circles are called as Apollonius circles. 3. For constructing the other circles, 3 tangent circles are taken every time and repeat the step 2. Fig. 2 shows iteration of the Apollonius Circles. Figure 2 APOLLONIUS Circular Fractal Geometries III. PROPOSED DESIGN Several individual studies have been made on the circular (Apollonius circles) and triangular (Sierpinski) fractal geometries independently.the proposed design includes formation of composite fractal structure through hybridization of circular and triangular fractal geometries. The proposed antenna is a compact structure with wide-band response characteristics and can be used for ISM Band applications. Figure 3 Composite Fractal All rights Reserved 276

3 2.3 Structural layout of the design Fig.4 below shows outline of the proposed antenna with dimensional specifications. Figure 4 Structure of proposed antenna with dimensional specifications The radius of the circle is calculated as Where, F= ( ) Table 2.1 Dimensional specification of proposed antenna structure A 39.2 B 43.5 D1 25 D D L 18.6 H 15.5 W 1.36 G 0.32 H 0.52 Where, a= Length of the fabricated monopole antenna b=height of the antenna D1=Diameter of the outer circle in the square patch. D2=Diameter of the first inner circle D3=Diameter of the second inner circle. L=Length of the ground plane. H=Height of the ground plane. w=width of the center conductor. g=width of the slot made between center conductor and ground plane. h=height of the space between radiating patch and ground All rights Reserved 277

4 IV.RESULTS AND DISCUSSION The design of antenna once ready by pen and paper approach is then simulated in Computer Simulation Technology (CST) Microwave Studio. CST Microwave Studio is an integral equation solver that is based on method of moments (MoM). Using above described methodology proposed antenna is simulated in CST and compared it performance with pre-existing antenna results. 4.1Simulated Antenna Structure A CPW-fed composite fractal structure monopole antenna for wideband ISM applications is designed, in which the current of proposed antenna structure is mainly distributed along the periphery of circular geometry. As a result, the current density is low in the central region of the antenna. If the central portion of the circular antenna configuration is removed still the current will not be affected and effective path of surface current will become longer. The antenna characteristics are dependent on D1, L, and H, h. It is also a function of dielectric constant. Here, the substrate used is FR4 with thickness of 1.6 mm, dielectric constant 4.4and the loss tangent of are used. Figure 5Simulated antenna using CST Microwave Studio 4.2 Return Loss Return loss is a suitable way to characterize the input and output signal sources. Return loss can be defined in S 11 db and is also referred to as the reflection coefficient of antennas. Reflection coefficient is proportional to the ratio of reflected power to the incident power of the antenna. Antennas usually radiate efficiently for particular range of frequencies. The proposed composite fractal antenna structure yields betterment in return loss ( db). Figure 6 Simulation Result of Return All rights Reserved 278

5 4.3 Voltage Standing Wave Ratio(VSWR) With reference to standing wave pattern, VSWR is defined as the ratio of the voltage maxima to the voltage minima.the higher the impedance mismatch, the higher the amplitude of standing wave. A perfect impedance matching would cause no voltage standing wave, so the proportion of the highest voltage to the lowest would be 1 (1:1). Permissible upper limit on practical values of VSWR is approximately 2. The composite fractal antenna configuration designed here obeys this limit. Figure 7 Simulation Result of VSWR 4.4 Radiation pattern and antenna gain Radiation pattern of an antenna is the fundamental parameter, which is nothing but a mathematical equation and/or the graphical representation characterizing the overall performance behavior of the antenna. Fig.8 Radiation pattern characteristics and antenna gain Here Ω is the normalized frequency and ε is the ripple factor, which is given as (2) The bandpass filter frequency response can be calculated as Ω ( ) Where =bandpass filter frequency 0= Mid-band frequency All rights Reserved 279

6 FBW=Fractional Bandwidth Two finite frequency attenuation poles a1 and a2 can be given as[5] Ω Ω (4) Ω Ω (5) V.CONCLUSION After trying different defected ground structures authors have used T shaped structure for this filter. Return loss and bandwidth improvement by application of T shaped structure can be observed in Fig 5. Stable insertion loss over the band of interest can be obtained by T shaped defected ground. By varying the dimensions of T shape, band control can also be achieved. Observing the return loss graph, it can be concluded that pass band for this filter is from 2.08 GHz to2.21 GHz. Insertion loss is db in the band of interest. Current flow distribution is given in Fig 7 for T shape and current flow distribution is given in Fig 8 for I shape. REFERENCES [1] Andrew C. Guyette, Ian C. Hunter, and Roger D. Pollard, The Design of Microwave Bandpass FiltersUsing Resonators With Nonuniform Q,IEEE Transactions On Microwave Theory And Techniques, Vol. 54, No. 11, November 2006 [2] Jia-Sheng Hong, M. J. Lancaster, Microstrip Filters for RF/Microwave Applications, New York: John Wiley & Sons, 2001 [3] David m. Pozar, Microwave Engineering, 2nd edition,wiley publication [4] G.L. Matthaei, L. Young and E.M.T. Jones, Microwave filters, impedance-matching networks, and coupling structures, Dedham, MA: Arthec House 1964 [5] Jia-Sheng Hong, and Michael J. Lancaster, Design of Highly SelectivebMicrostrip Bandpass Filters with a Single Pair of Attenuation Poles at Finite Frequencies,Ieee Transactions On Microwave Theory And Techniques, Vol. 48, No. 7, July 2000 [6] Gary Breed, An Introduction to Defected Ground Structures in Microstrip Circuits,High Frequency Electronics,november 2008 [7] L. H. Weng, Y. C. Guo, X. W. Shi, and X. Q. Chen, An Overview On Defected Groundstructure,Progress In Electromagnetics Research B, Vol. 7, , 2008 [8] Chirag Garg, Magandeep Kaur, A Review of Defected Ground Structure (DGS) in Microwave Design,International Journal Of Innovative Research In Electrical, Electronics, Instrumentation And Control Engineering,Vol. 2, Issue 3, March 2014 [9] Y. Guo and Q. Wang, "An Improved Parameters Extraction Method for Dumbbell-Shaped Defected Ground Structure," Engineering, Vol. 2 No. 3, 2010, pp [10] PARUI, K. S., DAS, S. A new defected ground structure for different microstrip circuit applications. Radioengineering, 2007, vol. 16, no. 1, p [11] Mrinal Kanti Mandal and Subrata Sanyal, A Novel Defected Ground Structurefor Planar Circuits, Ieee Microwave And Wireless Components Letters, Vol. 16, No. 2, February 2006page All rights Reserved 280