A NOVEL DESIGN OF MULTIBAND SQUARE PATCH ANTENNA EMBEDED WITH GASKET FRACTAL SLOT FOR WLAN & WIMAX COMMUNICATION Amit K. Panda 1 and Asit K. Panda 2 1 Department of ECE, Guru Ghashi Das Central University, Bilashpur, India 2 Department of ECE, National Institute of Science & Technology, Berhampur, India ABSTRACT A compact multiband patch antenna embedded with gasket fractal slots is proposed in this paper. The structure consists of square patch element with modified gasket slots on both radiating edge side. The antenna is fed by 50Ω co-planar waveguide (CPW) to make the structure purely planar. The investigation took place ranges between 1-7.5 GHz using CST MWS electromagnetic simulator. There are 3 resonant frequencies appeared at 2.45GHz, 3.6GHz & 5.6 GHz. From the return loss plot it is seen the antenna achieved the IEEE Bluetooth / WLAN (2.4-2.484 GHz), WiMAX (3.4-3.69 GHz) & WIFI (5.1-5.825 GHz) frequency band with -10 db return loss and also nearly omni-directional radiation patterns achieved. The peak realized antenna gain is around 5dB in all distinct bands. K EYWORDS: Self-similar, fractal, CPW, Sierpinski gasket, WiMAX, WLAN. I. INTRODUCTION Due to rapid growth of wireless communication technology, the necessities to cover multiple applications with a single antenna element have been developing extensive research on it. Traditionally, each antenna operates at a single or dual frequency bands, where different antenna is needed for different applications. This will cause a limited space and place problem. In order to overcome this problem, multiband antenna can be used where a single antenna can operate at many frequency bands. So, this has initiated antenna research in various directions, one of which was using fractal shaped antenna element [1]. Fractal antenna [2] has very good features like small size & multiband characteristic. Most fractal objects have self -similar with different scaling and spacefilling geometrical properties [3-5]. The fractal shape carried out by applying the infinite number of iterations using multiple reduction copy machine (MRCM) algorithm [6].Till now, many different antennas have been designed using different configurations to design multiband antenna such as, sierpinski gasket [7], multiple ring [8], hexagonal fractal [9] and circular fractal slot antenna [10]. Electric Circuits are of three types 1D (e.g. transmission line), 2D (e.g. microstrip line) and 3D (e.g. waveguides). The patch and the ground are placed in the same plane (co-planar) which makes the design purely planar structure. In particular, a great interest in coplanar waveguide (CPW) fed antennas has been seen in the literature because of their many attractive features such as, simplest structure of a single metallic layer, no soldering point and easy integration with active devices or MMICs[11]. Here in this paper we have presented a square patch antenna embedded with a modified sierpinski gasket slot which exhibits a large reduction in size along with multiband operation. The antenna was fed by CPW-like matching section which suits for WLAN, WIMAX & WIFI applications. The design procedure of the proposed geometry was depicted in Fig. 1. The purposed fractal geometry was constructed using square patch element and gasket fractal slot. The initial geometry of antenna at 0 th 111 Vol. 3, Issue 1, pp. 111-116
iteration has been taken a square patch element. Then at 1 st iteration the square patch was etched with gasket fractal slot on both radiating edge side of patch. Similarly, third and fourth iteration were achieved with the reduced scale and overlapping portion was subtracted from the inner square metallization respectively. This process of dropping the central continues for n th iteration to generate purposed fractal structure. The iteration order was limited to 2 nd iteration due to tolerance and complexity in fabrication. The scale factor will determined the high of each sub gasket and is given as: hn δ = 2 (1) h n+ 1 II. (a) (b) (c) Figure 1. Design procedure of purposed fractal structure geometry upto 2 nd iteration ANTENNA CONFIGURATION The proposed multiband antenna prototype was illustrated in Fig. 2. The entire dimensions of the antenna were 52mm 62 mm. The 50-SMA connector was used to feed the antenna at the CPW line. The design of the antenna starts with a single element using basic square patch microstrip antenna operating at frequency 1.8 GHz using an electromagnetic solver (CST MWS).The dimension of the antenna was determined from the equation of the patch antenna design equation. The antenna was designed up to 2nd iteration process. It was designed on FR-4 substrate with thickness of the substrate = 1.59 mm. (1/16 ), ε r = 4.21 & tan (δ) = 0.019 respectively and where the radiating element was chosen as copper clad. The structure was fed using CPW Feed.The width (W) of the ground plane on either side of the CPW central strip was 19.5 mm and its length (L g ) is 28.5 mm. The spacing (g) between ground plane and central conductor is 0.5mm and the separation (h) between ground plane and patch was1 mm considered. Figure 2. Square patch antenna embeded with gasket slots The purposed multiband antenna structure was constructed using square and gasket slots on both radiating edges of square patch. For generation of gasket slot, it starts with a gasket patch element, and then the central Inverted gasket was removed with vertices that are located at the midpoints of the sides of the original Gasket. This process was repeated for the three remaining Sectoral until 2 nd iteration in this particular case, so three scaled versions of the Sierpinski gasket were found on the antenna. The scale factor among the three gaskets was δ=2. Three scaled versions of the Sierpinski gasket, the first sub-gasket is 3 rd order Sierpinski of height 13mm, the second sub-gasket was second order Sierpinski of height 26 mm and the third is 1 st order Sierpinski of height 52 mm. 112 Vol. 3, Issue 1, pp. 111-116
III. RESULT AND DISCUSSION 3.1 Return Loss Characteristics The proposed antenna was simulated & analyzed using CST Microwave studio (CST MWS) between the frequencies 1-10 GHz. From the return loss plot as shown in Fig. 3, it was found that the antenna was matched in 3 resonant frequencies effectively appeared at 2.4 GHz, 3.61GHz, and 5.58 GHz respectively for 2 nd iteration. The return losses in all 3 bands were quite good. The 1 st impedance BW at 2.4 GHz was 105 MHz covering IEEE Bluetooth/WLAN band (2.2 2.56 GHz) with return loss - 35 db, the 2 nd impedance BW at 3.6GHz was 112 MHz covering WiMAX band (3.35-3.50 GHz) with return loss -22 db and the 3 rd impedance BW was 150 MHz covering WIFI band (5.1-5.825 GHz) respectively. 3.2 Effect of Width of the CPW Feed (W1) Figure 3. Simulated return loss A parametric study was done by changing the width of CPW feed for better matching section. Fig. 4 depicts the simulated return loss curves for different CPW feed widths (W1=2.7, 2.925, 3.15, 3.375 and 3.6 mm).when Ws increased from 3 to 4 the impedance matching of the antenna gets better. This fact gives further indication that a better impedance matching can be obtained by optimizing the width of central conductor W1 =3.6mm. It was noticed that the resonant frequencies shift significantly for the five different W1. When W1 is narrowed, the resonant frequency decreased dramatically, leading to the variations of the operating bandwidth range of the antenna. When W1 was increasing, the resonant frequency as well as S 11 increasing significantly. The return losses in all five bands are acceptable and all bandwidths are wider. Figure 4. Simulated reurn loss curves for different width CPW feed From the return loss plot it was seen that the optimized result for the antenna suited for IEEE Bluetooth/WLAN (2.4-2.484 GHz) & WIMAX (3.4-3.69 GHz) applications was attained at W1=3.6mm. 3.3 Gain vs. Frequency The simulated peak gain of the proposed antenna is plotted in Fig. 5. It is seen that gain level was achieved throughout the band. As observed in fig.5, gain vs. frequency plot, it was found that the gain was around 4.2 db at lower frequency band and were around 6 db at higher band. 113 Vol. 3, Issue 1, pp. 111-116
Figure 5. Gain versus frquency 3.4 Current Distribution & Radiation Pattern The current density and radiation patterns were analyzed using CST Microwave Studio. With a series of simulations it was seen that the magnetic current at the central gap & the electric current on the patch region of the antenna around the gap is crucial for resonance & radiation characteristics of such antenna. Simulation current density on the surface of the antenna at 2.4 GHz, 3.61GHz and 5.6 GHz were shown in Fig.6. It was observed as the number iterations was increased, multiple resonant frequencies obtained but the radiated power from the antenna was found to deteriorate (a) (b) (c) Figure 6. Current density distribution on antenna surface at (a) 2.4 GHz, (b) 3.61 GHz, (c) 5.6 GHz 114 Vol. 3, Issue 1, pp. 111-116
The simulated normalized radiation patterns at all distinct frequencies for φ = 0 0 &90 0 were shown in Fig. 7. It was observed that the H-plane patterns were reasonable over the entire operating bandwidth. The radiation patterns were consistent for the different resonant frequencies for 2 nd iteration. (a) E- θ for φ=90 0 at 2.4 GHz (b) E- θ for φ=90 0 at 3.61 GHz (c)e- θ for φ=90 0 at 5.6 GHz Figure 7. Simulated Normalized radiation patterns of purposed patch antenna for φ = 90 0 at (a) 2.4 GHz, (b) 3.61GHz (c) 5.6GHz An interesting phenomenon was phenomenon is observed that with increasing resonant frequencies the patterns show more undulations. The pattern for lower bands are more omni directional & the cross polar isolation are very minimum but there are side lobes existing at higher frequency. IV. CONCLUSION A novel compact CPW fed compact square patch antenna embedded with Gasket fractal slot was designed & simulated for multiband operations. The simulated results indicate that the antenna exhibits a good return loss, and the antenna gain was above 5 db at the designed frequencies and other multiband frequencies suitable for IEEE Bluetooth/WLAN (2.4-2.484 GHz), WiMAX (3.4-3.69 GHz) & WIFI (5.1-5.825 GHz) wireless communication applications The design was implemented by using CST MWS electromagnetic simulation tools. The self similarity in the structure for the 2 nd iteration leads to multiband operation of the antenna. The key parameters that influence antenna performance have been analyzed to gain an insight into antenna operation. Hence a good antenna performance over the operating frequencies over the whole band was obtained. 115 Vol. 3, Issue 1, pp. 111-116
ACKNOWLEDGMENT The authors would like to thank, CST Company, India for their support in CST EM tool. The authors are grateful to the anonymous reviewers for their constructive & helpful comments & suggestions. REFERENCES [1] B. B. Mandelbrot, The Fractal Geometry CfNature, Freeman, 1983. [2] H.Jones, et al, Fractals and chaos, A.J.Crilly, R.A.Earnsshaw, and H.Jones, Eds., Springer-Verleg., Newyork, 1990. [3] C. Puente, J. Romeu, R. Pous, A. Cardama, On the behavior of the Sierpinski multiband antenna, IEEE Trans. Antennas Propagat., vol. 46, pp. 517-524, Apr. 1998. [4] Werner D.H., Mittra R, Frontier of electromagnetic, Wiley-IEEE Press, Newyork, 1999. [5] D. H. Werner, S. Ganguly, "An overview of Fractal Antenna Engineering Research", IEEE Antennas and Propagation Magazine, vol. 45, pp.38-57, 2003. [6] H.O.Peitgen., et al, Chaos and Fractals, A.J.Crilly, R.A.Earnsshaw,and H.Jones, Eds., Springer- Verleg., Newyork, 1990. [7] C. Borja and J. Romeu, Multiband Sierpinski fractal patch antenna, Antennas and Propagation Society International Symposium, IEEE, vol. 3, pp. 1708-1711, July 2000. [8] C. T.P. Song, Peter S. Hall and H. Ghafouri-Shiraz, Multiband multiple ring monopole antennas, IEEE Transactions Antenna & Propagation, vol. 51, pp. 722-729, Apr 2003. [9] Kan Philip Tang and Parveen Wahid, Hexagonal Fractal Multiband Antenna, Antennas and Propagation Society International Symposium, IEEE, vol. 4, pp. 554-557, June 2002. [10] Ji-Chyun Liu, Der-Chyuan Lou, Chin-Yen Liu, Ching-Yang Wu and Tai-Wei Soong, Precise Determinations of the CPW-FED Circular fractal slot antenna, Microwave and Optical Technology Letters, vol. 48, pp.1586-1592, Aug 2006. [11] Ip, K.H.Y., Kan, T.M.Y., and Eleftheriades, G.V.: A single-layer cpw-fed active patch antenna, IEEE Microw. Guide. Wave Lett., 2000, 10, pp. 64 66 Authors Biography Amit K. Panda received his M.Sc in Electronics from Berhampur university& the Master of technology degree in Electronics design technology from Tezpur cental University. He is currently working as Asst. professor with the Department of electronics and communication Engineering, Guru Ghasidas Central University, Bilaspur.His main Research interests are in FPGA based system design, VLSI digital design, Network implementation on FPGA, RF and microwave control devices and semiconductor components. Amit K. Panda is a faculty in ECE department at National institute of science & Technology (NIST), Berhampur, India. He obtained his M.Tech in ECE from NIST under Biju patnaik Technical University (BPUT) in 2009, completed his B.Tech in ECE in 2003 from NIST,.Currently continuing his Ph.D work on metamaterial. His current area of interest are DNG material, metamaterial antenna, invisible cloaking, Multiband & wideband patch antenna, fractal antenna. He has presented 8 international conference papers. 116 Vol. 3, Issue 1, pp. 111-116