A RECONFIGURABLE SWITCHED BEAM ANTENNA USING ACTIVE CYLINDRICAL FREQUENCY SELECTIVE SURFACE Mohamed Aymen El Cafsi 1 , Mourad Nedil 2 , Lotfi Osman 1 and Ali Gharsallah 1 1 Lab. CSEHF, Faculty of Sciences of Tunis, Tunis EL Manar University, 2092, Tunisia 2 UQAT- LRTCS - Université de Québec en Abitibi-Témiscamingue and underground communications research laboratory (LRTCS), 450 3e avenue, Val d'Or, Qc, J9P 1S2, Canada. ABSTRACT A novel design of reconfigurable antenna using active cylindrical Frequency Selective Surface (FSS) operating at 5.8 GHz is presented. The structure is composed of an omnidirectional printed slot array antenna placed at the center of the FSS surface. A discontinuous strip is used as unit cell of FSS structure where a PIN diode is placed at the discontinuity. The control of diode state allows the sweep of radiation pattern in the entire azimuth plane offering four beams with 3-dB beamwidth of 70°.The proposed antenna has simulated and analyzed using CST Microwave studio. The obtained gain is 12 dBi with -10dB bandwidth of 1.72% at the centered frequency 5.8 GHz. Index Terms— Reconfigurable Antenna, Frequency Selective Surface (FSS), Slot array antenna, Radiation Pattern. 1. INTRODUCTION Reconfigurable antennas (RA) have found a lot of attention in this decade due to its ability to improve the performances of wireless communication systems by changing their operating characteristics such as operating frequency, radiation pattern or polarization state [1][2]. The use of radiation pattern as reconfigurable parameter can improve the characteristics of communication channel by reducing interference and multipath fading phenomena and increasing the channel capacity. However, Pattern reconfigurable antenna permits to avoid interferences, improve the coverage of base station and save energy by steering directly the main lobe in the user direction [1]. Reconfigurable radiation pattern can be used as a scanning beam technique to create switched beam smart antennas and replacing conventional methods which are mechanical and electrical scanning [3]. Usually, the mechanical scanning is done by placing antenna onto turntable [3] while the electrical scanning is realized by using phased arrays and beam switch arrays with their complex feeding networks and phase shifters [3]. Recently, Electromagnetic Band Gap (EBG) structures, which are artificial periodic materials, are used to control the propagation of electromagnetic waves in a specific frequency band depending on the angle of incidence and the polarization state [4]. Frequency Selective Surface [5][6] or Partially Reflecting Surface (PRS),which are type of EBG structures, are used to produce various devices in antenna applications such as reflector antenna systems [7] and random. It allows also to create smart RA with a switching beam using active elements such as PIN diodes. Many reconfigurable pattern antennas have been proposed in [8-13] which are composed of an omnidirectional dipole or coaxial dipoles array surrounded by an active cylindrical FSS structure composed of metal discontinuous strips [8-12] where PIN diodes were placed in the discontinuity. However, pattern reconfigurable antenna using dipole as source suffers from low gain [9] which can be improved by using the multilayer FSS technique. Although, this technique increases the complexity of system in term of cost and decreases the efficiency. To exceed these cited drawbacks, dipole is replaced by an array of dipoles or Electromagnetically Coupled Coaxial Dipoles (ECCD) which, between two near dipoles, two pipes are used to obtain in-phase excitation of array and thus ensure a good impedance matching [12]. The use of pipes also complicates the design of ECCD in terms of coupling between radiators in arrays. In this paper, to avoid pipes and multilayer FSS technique, a novel omnidirectional source is used and consists of a planar slot array antenna that was proposed in [14]. The effect of parameters of the source on its operating frequency and the variation of radius of FSS cylinder and the number of strips on radiation pattern are discussed. The proposed antenna was analyzed using CST Microwave Studio [15] and numerical results were performed. 2. FSS UNIT CELL The proposed unit cell, presented in Fig.1, is composed of metallic discontinuous strip where a PIN diode is placed in the discontinuity. According to the state of the diode, the strip has a reconfigurable Transmission/Reflection coefficient basing on the equivalent RC circuit of the diode [12]. When the diode is ON, it is equivalent to a resistor and 2013 26th IEEE Canadian Conference Of Electrical And Computer Engineering (CCECE) 978-1-4799-0033-6/13/$31.00 ©2013 IEEE