Reconfigurable Fractal Tree Antenna for Multiband Applications Hüseyin Altun 1 , Erdal Korkmaz 1 , Bahattin Türetken 2 , 1 Department of Electrical and Electronics Engineering, Fatih University, Istanbul, Turkey haltun@fatih.edu.tr , ekorkmaz@fatih.edu.tr 2 The National Research Institute of Electronics and Cryptology (UEKAE), TUBITAK, Gebze, Turkey bahattin@uekae.tubitak.gov.tr Abstract This paper evaluates reconfigurable specification of the fractal tree antenna. Fractal tree antenna fed by a 50 ohms round coax from its middle. Making PIN-diodes on or off state, the characteristic of antenna changes and it results changes in the operation frequency and radiation pattern. The proposed antenna demonstrates reconfigurable frequency range from 1.51 GHz up to 8.6 GHz. Analysis of the antenna has been done by means of commercial software CST Microwave Studio to discuss the impression of different dimensional parameters by controlling the PIN diode switches on radiation pattern, directivity and operational frequency. 1. Introduction With the rapid development in communication, reconfigurable antennas gain great attention. Reconfigurable antennas have more benefits and better prospects compared with conventional antennas since they show interesting characteristics providing various functions, for example, resonant frequency, radiation patterns and polarization reconfigurabilities [1-2]. The most common application about reconfigurable antenna is related to the operation frequency [3-4] since it might be the simplest feature to alter. The literature become narrower when it comes to radiation pattern reconfiguring since it is related to the radiation principles of each antenna which cannot be altered in many ways [5]. PIN diodes are generally used as switching devices for RF and microwave front-end communication systems since they have several crucial properties such as, low insertion loss, good isolation, low power handling and low cost [5]. The term fractal, means broken or irregular fragments, was originally entitled by Mandelbrot [6] to describe a family of complex shapes that possess an inherent self-similarity in their geometric structure. As a result of small observation in the nature a lot of example for fractal can be seen as trees, clouds, snowflakes, leaves, galaxies and much more. Fractal tree structures can be applied into antenna design to produce multiband characteristics [7-9]. The aim in this paper is showing the design of a new shape of fractal tree antenna for multiband applications which is made reconfigurable by using of PIN diodes. By switching PIN diodes, the resonant frequency and radiation pattern variation simulation is presented. 2. Antenna Design Antenna schematic is presented from its top view in Figure 1.a and perspective view in Figure 1.b. The antenna is designed on a substrate of 80x80 mm surface and 1.6 mm thickness with Rogers RT5880 (lossy) material having 2.2 r ε = . The ground has been chosen from PEC material with a thickness of 0.1 mm. The antenna is fed by a 50 ohm round coax. The inner conductor of the coax has diameter of 0.689 mm and the shield is 2.13 mm Rogers RT5880. The feeding line is 5 mm long from end to top. As can be seen in Figure 1.a each part of the antenna has been numbered for the description. Part 1 is called the root and it is on the feed. Its mission is delivering the power to the parent branch. Part 2, 4, 6 and 8 are parent branches and they are connected to the root with PIN diodes; D12, D14, D16, D18. For example D12 is the diode between the root (part 1) and parent branch (part 2). 978-1-4244-6051-9/11/$26.00 ©2011 IEEE