A New Approach to Optimal Design of T-shaped Tri-Band Fractal Microstrip Patch Antenna for Wireless System Applications Ms. Monika Nandal 1, Er. Sagar 2 and Dr. Rajesh Goel 3 1 MTech Student, Samalkha Group of Institutions, Samalkha 2 Assistant Professor, Samalkha Group of Institutions, Samalkha 3 Professors, Samalkha Group of Institutions, Samalkha Abstract Two iterations of fractal geometry are applied to form T-shaped fractal antenna. This antenna is designed using cantor fractal geometry. This antenna is obtained by making square of dimensions 36 by 36 mm and ground of dimensions 50 by 50 mm. coaxial feed has been used to feed antenna. This antenna has been designed using IE3D simulation software. This antenna resonates at 3.5 GHz, 7.4 GHz and 9.7 GHz. This antenna had return loss. This antenna resonates at 3.5 GHz, 7.7 GHz and 9.7 GHz with a return loss of -19.26 db, -22.74 db and -22.63 db. This antenna has gain of 3.24 dbi, 5.41 dbi and 4.04 dbi at corresponding frequencies. Bandwidth of antenna showed improvement a lot. This antenna is having bandwidth of 130 MHz, 1.3 GHz and 800 MHz at these frequencies. This antenna finds its application for C Band, X band and Wi-Max applications. Best part of this design is that it has good bandwidth in C band which is desired full. Keywords: Microstrip, T-shape, Wi-Max, Fractal, Multiband. 1. INTRODUCTION In order to design any communication system, one may require transmitter, recciver and channel. Transmitter and receiver module require antenna to transmit and receive. Antenna is selected to have small size; it must cover different wireless applications. If one may require multiband antenna, one solution is to have different antenna for different wireless applications. But by applying fractal geometry to antenna, one may design antenna for different applications. One of fast growing segment of communication industry is wireless communication which finds application in many areas. Microwave spectrum is usually called as electromagnetic spectrum, since it range from 1GHz to 100 GHz. Microwave bands are classified into many frequency bands. Since most common applications are within 1GHz to 40 GHz. Hence different bands within this range are L band (1-2 GHz), S band (2-4 GHz), C band (4-8 GHz), X band (8-12 GHz), K u band (12-18 GHz), K band (18-26.5 GHz) and K a band (26.5-40 GHz). An antenna is a transducer that transmits or receives electromagnetic waves. The antenna transforms electric current into EM by transmitting a signal into radio waves and transforms electromagnetic waves into electric current by receiving. One of major issue for antenna design is to make small size, multiband and wideband antenna.microstrip antenna s are best useful as they will make it good. Microstrip antenna consists of patch and ground separated by a dielectric called substrate. Although these antennas are having number of advantages but they suffer from a number of disadvantages, like these antenna may have large return loss, low gain, small bandwidth and lack of multi banding. Characteristics of antenna may be improved by making use of techniques. These techniques are use of fractal geometry, cutting slot in patch and making use of defected ground structure. In this paper, T shape fractal patch antenna is designed using cantor fractal geometry. Antenna in [1] has good characteristics but has bands above 6 GHz and also it has slight large size, so I shaped concept has been changed to T- shape fractal geometry by reducing size. Further parametric analysis can be applied to make antenna good for multiband and wideband applications. 2. BACKGROUND OF ANTENNA Kohli et al. [1] presented I-shaped fractal patch antenna for different wireless applications. Three iterations of Minkowski fractal patch antenna have been applied which caused antenna to resonate at four different frequency bands. Chitra et al. [2] Microstrip antenna with two L slot for Wi-Max and WLAN applications had been designed. This antenna was fed by coplanar waveguide feeding technique. Ghatak et al. [3] Proposed sierpinski carpet fractal antenna for ultra wideband applications. This antenna was having a hexagonal boundary. This antenna covered frequency band of 3GHz to 12 GHz at VSWR less than 2.Attri et al. [4] presented fractal patch antenna for wireless applications. This antenna was mostly used for personal communication applications. Sierpinski carpet fractal geometry has been used in which every square was divided into nine sub squares.kaushik et al. [5] had designed microstrip antenna with wide and omnidirectional radiation pattern with maximum energy in major lobe. This antenna was having small size of 34X 20 mm 2. This antenna had a large bandwidth of 1.3 GHz, gain of 2.65 dbi and a return loss of -28.82 db. Proposed antenna can be used for a number of wireless applications which were Wi-Max, IMT and WLAN applications. Varadhan et al. [6] used tree shape Volume 3, Issue 6, June 2014 Page 256
fractal geometry on microstrip patch antenna to form fractal microstrip patch antenna. These were used to identify radio frequency. Vinoy et.al [7] designed multiband ring fractal patch antenna using multiport network approach. Sun et al. [8] obtained large bandwidth on a thin substrate by making a rectangular slot. Chainool et al. [9] applied fractal geometry on loop antenna to make antenna useful for USB dongle application. Bansal et al. [10] applied property of self-similar characteristics of fractal geometry to obtain multiband antenna. Because of self-similar characteristics, current flow through different paths in fractal microstrip antenna hence multiband characteristics will be obtained. By carrying out literature survey problem was formulated. 3. ANTENNA DESIGN In order to design fractal microstrip antenna, dimensions are selected depending on frequency. Square patch of dimensions 36 mm is taken. FR-4 is used as substrate having dielectric constant of 4.4 and loss tangent of 0.02. Ground plane is having dimensions of 50 mm. This antenna has small size as compare to [1]. Fractal geometry used to make this design is cantor shaped fractal geometry. In cantor geometry every time in every iteration middle section is removed to form self-similar structure. Dimensions of proposed fractal antenna are shown in table 1 Table 1: Dimensions of Reference Antenna Variable Value [1]Length of patch 36 mm [2]Width of patch 36mm [3]Length of ground 50 mm [4]Width of ground 50 mm [5]Thickness of substrate 2.4 mm [6]Feeding technique used Coaxial Feeding Technique [7]Substrate used FR-4 [8]Dielectric constant 4.4 [9]Feed point (0, 4, 0) [10]First Iteration slot cut size 12X18 mm 2 [11]Second iteration slot cut size 4X9 mm 2 Fractal geometry algorithm is applied is cantor shape fractal geometry algorithm as shown in figure 1. Figure 1:Cantor Shaped Fractal Geometry Algorithm Initially, square patch of length 36 m is taken and results are analyzed. The square patch is shown in figure 2. Coaxial feed is given at feed point (0,8,0). Results are analyzed corresponding to this initiator. Figure 2: Zeroth Iteration Fractal Geometry After that first iteration of fractal geometry is applied to make T shape patch. This T shape patch is obtained by cutting two rectangle of dimensions 18 X 12 mm. The entire length is divided into three parts of 12 mm each and entire width is divided into two equal parts. Scale factor of one by three is chosen length wise and half along width side. Feed to antenna is given at feed point (0, 8, 0). The geometry of T shape patch is shown in figure 3. Volume 3, Issue 6, June 2014 Page 257
Figure 3: First Iteration Fractal Geometry By cutting slot, area of patch decreases. Second iteration of fractal geometry is applied by cutting slot of 4 X 9 mm 2 from rectangles of size 12 X 18 mm 2. Each rectangle of size 12 X 18 mm 2 has been divided into six parts and two equal parts have been cut out so as to obtain self-similar structures. Feed to antenna is coaxial feed and feed point is adjusted such that impedance matching takes place. Feed is given at (0, 4, 0). Geometry of all three iterations is shown in figure 4.These geometries as shown in Figure 4: Second Iteration Fractal Geometry figure2, 3 and 4 shows above self-similarity characteristics. These dimensions show as number of iterations increases, area decreases. Beyond a certain level of iteration, complexity increases and fabrication of antenna becomes difficult 4. RESULTS AND DISCUSSION In this section, simulation results of different iterations of fractal geometry are compared. T shape fractal antenna is made by cutting slots as shown in figure 2,3 and 4. These cause self-similar T-shaped structure. Return loss vs. frequency for various iteration of T-shaped fractal geometry are shown in figure 5. Figure 5: Return Loss Vs. Frequency for Different Fractal Iterations of T-shaped FMPA Volume 3, Issue 6, June 2014 Page 258
From figure 5 it is found that characteristics of antenna increases as number of iterations increases, initially square antenna resonates at 3.8 GHz, 4.4GHz and 7.9 GHz with return loss of -20.43 db, -14.83 db and -10.39 db, gain of 2.68 dbi, 0.50 dbi and 4.4 dbi and bandwidth of 135 MHz, 120 MHz and 25 MHz. since characteristics of antenna at zeroth iteration are not good so fractal geometry has been applied to improve characteristics. Two slots are cut as shown in figure 3. This antenna resonates at 4 GHz, 6.2 GHz, 7.8 GHz and 8.4 GHz with return loss of -13.43 db, -13, -11.60 db, - 13.97 db. In this iteration of fractal geometry, gain of antenna show improvement, as antenna is having gain of 1.26 dbi, 1.41 dbi, 4.32 dbi and 2.92dBi. By applying third iteration of fractal geometry self-similar structures as shown in figure 4. are obtained. This antenna had less return loss and good bandwidth as compare to previous iterations. This antenna resonates at 3.5 GHz, 7.7 GHz and 9.7 GHz with a return loss of -19.26 db, -22.74 db and -22.63 db. This antenna has gain of 3.24 dbi, 5.41 dbi and 4.04 dbi at corresponding frequencies. Bandwidth of antenna showed improvement a lot. This antenna is having bandwidth of 130 MHz, 1.3 GHz and 800 MHz at these frequencies. Further radiation patterns at 3.5 GHz, 7.4 GHz and 9.7 GHz have been shown in figure 6(a), 6(b), and 6(c). Figure 6: Radiation Pattern of T-shaped FMPA at (a)3.5 GHz, (b) 5.7 GHz and (c) 7.7 GHz Table 2 shows comparison of results of different iterations of T-shaped fractal geometry applied on square patch as shown in figure 2,3 and 4. Results are analyzed in terms of return loss, gain, directivity and bandwidth. Iteration Number Table 2: Comparison Results of Different Iterations of T-shaped FMPA Resonance Return Loss Gain (dbi) Frequency (GHz) (db) 0 th Iteration 3.8-20.43 2.68 135 4.4-14.83 0.5 120 7.9-10.39 4.40 25 1 st Iteration 4-13.43 1.26 90 6.2 --13 1.41 105 7.8-11.59 4.32 130 8.4-13.97 2.92 180 2 nd Iteration 3.5-19.26 3.24 130 7.4-22.74 5.4 1200 9.7-22.63 4.04 800 Band width (MHz) Results showed that as the number of iterations increased, results of antenna showed improvement, VSWR of antenna for different frequencies is shown in figure 7. VSWR stands for voltage standing wave ratio. At resonance frequency, VSWR must be less than two but it must be greater than unity. VSWR is measure of return loss, more negative return loss, more better is system. Bandwidth can also be defined in terms of VSWR. Range of frequency on either side of resonant frequency where VSWR is between one and two defines bandwidth. This antenna has VSWR of 1.244, 1.157 and 1.159 at frequencies 3.5 GHz, 7.4 GHz and 9.7 GHz. It is required that voltage standing wave ratio is with in limit. Higher value of VSWR, smaller be return loss in negative db scale which is not just correct. There are different parameters which can be taken into account. Volume 3, Issue 6, June 2014 Page 259
Figure 7: VSWR Vs. Frequency for Proposed Antenna Smith chart is best method of representing complex frequencies with respect to represent complex impedances with respect to reflection coefficient. Figure 8 shows smith chart of proposed antenna. Figure 8:Smith Chart of Proposed Antenna 5. CONCLUSION Multiband T shaped fractal patch antenna has been presented in dissertation. Out of different designs, with different thickness and feed point. Antenna using FR-4 as substrate, with thickness of 2.4 mm and feed point of (0,4 ) is finalized. This antenna resonates at 3.5 GHz, 7.4 GHz and 9.8 GHz with return loss of -19.26 db, -22.74 db and -22.63 db. Further this antenna had gain of 3.24 dbi, 5.4 dbi and 4.04 dbi at corresponding frequency. This antenna is having large bandwidth of 1.2 GHz in C band at 7.4 GHz and 800 MHz in X band at 9.8 GHz. Further this antenna can be useful for Wi-Max, RADAR, Satellite communications, C Band and X band applications References [1] Kohli S., Singh S. and Marwaha A., 2013 Design and Optimization of Multiband Fractal Microstrip Patch Antenna for Wireless Applications, Accepted for Proceedings of 5th IEEE International Conference on Computational Intelligence and Communication Network, Mathura, India., pp-32-36. [2] JothiChitra R, Nagarajan V. 2013 Double L-slot microstrip patch antenna array for WiMAX and WLAN applications. Computers and Electrical engineering. pp-1-16. [3] Ghatak Rowdra, Karmakar Anirban, and Poddar D.R., 2013. Hexagonal Boundary Sierpinski Carpet Fractal Shaped Compact Ultra wideband Antenna with Band Rejection Functionality, International Journal of Electronics and Communications, Vol. 67, page 250-255. [4] Attri A. And Kansal A.,2013 Improved Performance Of Sierpinski Carpet Based Fractal Antenna Using Stacked Configuration International Journal of Scientific & Engineering Research, Volume 4, Issue 8., pp-220-224. [5] Kaushik S.,DhillonS.S. 2013. Reactangular Microstrip Patch Antenna with U-Shaped DGS Structure for Wireless Applications 5 th International Conference on Computational intelligence and Communication networks, pp-27-31. Volume 3, Issue 6, June 2014 Page 260
[6] Varadhan C., Pakkathillam J. Kizhekke, Kanagasabai M., Sivasamy R., Natarajan R. and Palaniswamy S. Kumar, 2013. Triband Antenna structures for RFID Systems Deploying Fractal Geometry, IEEE Letters on Antennas and Wireless Propagation, Vol. 12, pp 437-440. [7] Behera S. and Vinoy K. J., 2012. Multi-Port Network Approach for the Analysis of Dual Band Fractal Microstrip Antennas, IEEE Transactions on Antennas and Propagation, Vol. 60, No. 11, pp 5100-5106. [8] Sun Xu-Bao, Cao Mao-Yong, Hao Jian-Jun and Guo Yin-Jing, 2012. A rectangular slot antenna with improved bandwidth, International Journal of Electronics and Communications, Elsevier, Vol. 66, pp 465-466 [9] Chaimool S., Chokchai C., And Akkaraekthalin. 8 th Nov 2012 Multiband loaded Fractal Loop Monopole Antenna for USB Dongle Applications. Electronics Letters, vol. 48, No-23 [10] Bansal P., Tayal S, 2012. Design and Analysis of Hollow Star Shape Fractal Antenna, Second International Conference On Advanced Computing and Communication Technologies. pp- 211-213. Volume 3, Issue 6, June 2014 Page 261