A Novel Pattern Reconfigurable Dipole-Yagi Antenna for Wireless Body Area Network (WBAN) Applications # E.N.Ahyat1, N. H.Ramli2, M. R. Kamarudin3, T. A. Rahman4 and M.F.Jamlos5, 1 Wireless Communication Centre (WCC), Faculty of Electrical Engineering Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia, [email protected], 2 [email protected] [email protected] 4 [email protected] 5Nature and Defense Centre (NDeC), School of Computer and Communication Engineering Universiti Malaysia Perlis (UniMAP), Perlis, Malaysia, [email protected] Abstract A novel pattern reconfigurable Dipole-Yagi antenna design, simulation and measurement are presented in this paper. The structure based of Yagi-Uda rationale consisting of director and reflector with four PIN diodes operates at 2.5GHz is proposed. Radiation pattern can be well reconfigured by turning the PIN diode switches on and off. Keywords : Reconfigurable Antenna, Radiation Pattern 1. Introduction Developing trend in reconfigurable antenna has been highly demanded due to enhancement of wireless wearable computing system. Reconfigurable antenna able to overcome the weaknesses and limitations of the previous antenna as this type of antenna provides better scanning resolution, flexibility and additional functionality [1]. Generally, it can be classified into three: resonant frequency, polarization and radiation pattern reconfigurable [2]. Pattern reconfigurable antenna has drawn huge attention as it enables the manipulation of radiation pattern to increase security by directing signals to intended users, improved beam steering capability and diversity system. Radio frequency PIN diodes, MEMS switches, and optical switches are the switching mechanism in order to varying radiation pattern [1, 3-7]. By adjusting the current paths and controlling the bias voltages of PIN diodes, antenna will be shifted to its maximum/minimum radiation direction, pattern and resonant frequency. However, the selection of switch type greatly depends on the switching speed demanded by the application and the switched power level [8]. Several approaches of controlling the switches states is offered to implement the reconfigurable antenna. These approaches allow changes of antenna fundamental characteristic [2,9]. This paper presented description and analysis of pattern reconfigurable antenna with the addition of copper tape replacing PIN diodes as RF switch. The antenna performances such as input return loss, bandwidth, and radiation patterns were obtained. 2. Antenna Design and Operational Mechanism The design and analysis of proposed antenna were performed using CST Microwave Studio. The antenna design is basically consist of a dipole in an array effectively operates as a driven and the combination of parasitic element referred as the reflector and director. The radiating element was constructed on the upper surface of FR4 printed circuit board (PCB) without ground plane and fed by a 20mm coaxial probe that is connected to the centre of the square patch. The dielectric constant and the thickness of the substrate are 4.7 and 1.6 mm respectively. For this design, it was required for dipole to be less than half a wavelength long or 0.47 times the wavelength [10]. The other dimension of proposed antenna is as follows: L1=30mm, L2=19mm, L3=3.5mm, P1=63mm, P2=50mm, D1=3.17mm, D2=6.67mm. Figure 1(a) shows the proposed reconfigurable antenna structures which is based on the design of printed yagi antenna. L1 L1 2nd SW D2 P1 L2 L2 D1 L3 L2 L2 3rd SW 4th SW L1 L1 st 1 SW (a)(a) (b) Figure 1: Geometry of Proposed Antenna (a) Details Design of Proposed Antenna (b) Placement of Switch for Pattern Reconfigurable The length of dipole and geometry of each passive element is critical in order to permit the antenna operates at 2.5GHz and radiates the expected radiation pattern. The antenna will produce the same characteristic when the switch is placed on the opposite position with each other. It is due to symmetry design of the antenna. In the simulations, diode was modeled as metal strips in ON state and was ignored in the OFF state. Pattern reconfigurable is achieved when the switch is placed in the middle of two passive element of the antenna. There are four position of switch that can be offered by this antenna depicts by Figure 1(b). When these passive elements are connected, it will act as a reflector while the other two will act as a director for this antenna. The copper tape is assumed as a PIN diode in the ON state and lengthened parasitic element works as a reflector. While, elimination of the copper tape from the fabricated antenna act as the OFF state and shortened parasitic element works as director. 3. Simulated and Measurement Result The prototype of proposed antenna was fabricated on FR4 substrate shown in Figure 2. The antenna measurement was tested on a vector network analyzer (VNA). Proposed antenna’s radiation pattern, return loss, directivity and gain are observed. Table 1 shows the simulated as well as measured return loss, radiation pattern, gain, directivity and current distribution of antenna under different bias states. For all four states, good impedance matching with less than -10 dB return loss is observed at 2.5GHz. The pattern is reflected by antenna’s reflector which is when two directors are connected by a switch as shown clearly by current distribution for 1st and 2nd switch. Hence, each of four states will produce different direction of pattern. When the 1st or 2nd switch is working, antenna offers end-fire pattern and broadside pattern when 3rd and 4th switch is ON. Figure 2: Prototype of the proposed antenna Table 1: Performance of Proposed Reconfigurable Antenna States/Current Return Loss(dB)/ Frequency(GHz) Radiation Pattern Distribution S-Parameter Magnitude in dB st 1 5 SW 0 -5 -10 S11/dB -15 -20 -25 -30 1 2 3 4 5 Freq/GHz Directivity=5.0dBi Simulation Measurement 2nd S-Parameter Magnitude in dB SW 5 0 -5 -10 -15 S11/dB -20 -25 -30 -35 1 2 3 4 5 Freq/GHz Simulation Directivity=5.0dBi Measurement rd S-Parameter in dB 3 SW 5 0 -5 -10 S11/dB -15 -20 -25 -30 1 2 3 4 5 Directivity=2.2dBi Freq/GHz Simulation Measurement S-Parameter Magnitude in dB 10 0 -10 -20 S11/dB -30 th 4 SW -40 -50 1 2 3 4 5 Freq/GHz Simulation Measurement Directivity=2.2dBi 4. Conclusion A pattern reconfigurable Dipole-Yagi antenna is presented in this paper. The existence of passive element proven that pattern reconfigurability is achieved when radiation pattern is reflected by the reflector and operates at 2.5GHz. The radiation pattern reconfigurable component is composed by deploying a PIN diode between two passive elements. Good impedance matching is obtained and fabricated antenna showed good agreement between simulated and measured return losses. This antenna will be highly potential for Wireless Body Area Networks communication system. References [1] J.W. Baik, S. Pyo, T.H. Lee, Y.S Kim, “Switchable Printed Yagi-Uda Antenna with Pattern Reconfigurable,” ETRIJournal on Volume 31, Number 3, June.2009 [2] J. Ryckaert, P.D. Doncker, R. Mwys, D.D. Le Hoye, S. Donnay, “Channel Model for Communication around Human Body,” Electronics Letter on Volume 40, Issue 9, April. 2004 Page(s): 543-544 [3] F. Romdhani, M. Denden, A Samet, “A Printed Reconfigurable Antenna for Communication System,” Mediterrannean Microwave Symposium, MMS, IEEE, 2009 [4] D. Jiawei, W. Angou, L. Hang, “A Simple Radiation Pattern Reconfigurable Printed Dipole Antenna,” 2009 3rd IEEE International Symposium on Microwave, Antenna, Propagation and EMC Technologies for Wireless Communications, MAPE, IEEE, 2009 [5] G.H. Huff, J.T. Bernhard, “Integration of Packaged RF MEMS Switches With Radiation Pattern Reconfigurable Square Spiral Microstrip Antennas,” IEEE Trans. Antennas Propag., vol. 54, pp. 464- 469, Feb. 2006. [6] S.Nikolaou, R. Bairavasubramanian, C. Lugo, I.Carrasquillo, D.C.Thompson, E. P. George,J. Papapolymerou, M. M. Tentzeris, “Pattern and Frequency Reconfigurable Annular Slot Antenna Using PIN Diodes,” IEEE Trans. Antennas Propag., vol. 54, pp. 439-448, Feb. 2006. [7] T.Y. Han, C.T. Huang, “Reconfigurable monopolar patch antenna,” Electronic Letters, Vol. 46 No. 3, 4th February 2010. [8] M.S. Parihar, A. Basu, S.K. Koul, “Polarization Reconfigurable Microstrip Antenna,” Centre for Applied Research in Electronics, Indian Institute of Technology Delhi, New Delhi-110016, India. [9] M.F. Jamlos, T. A. Rahman, M.R. Kamarudin, M.T. Ali, M. N. Md Tan, P. Saad, “A Beam Steering Radial Line Slot Array (Rlsa) Antenna With Reconfigurable Operating Frequency,” J. of Electromagn. Waves and Appl., Vol. 24, 1079–1088, 2010 [10]Z. Reto, “Printed Dipole Antenna”, University of Colorado, Bolder. Acknowledgements The authors wish to acknowledge Ministry of Higher Education (MOHE) for providing FRGS grant (Vot 78576) that enables this work to be accomplished and also special thanks to the members of Wireless Communication Centre (WCC), Faculty of Electrical Engineering, Universiti Teknologi Malaysia for their helps and kindness. .