618 PIERS Proceedings, Moscow, Russia, August 19–23, 2012 A Printed Fractal Based Slot Antenna for Multi-band Wireless Communication Applications Jawad K. Ali, Mahmood T. Yassen, Mohammed R. Hussan, and Ali J. Salim Microwave Research Group, Department of Electrical Engineering University of Technology, Baghdad, Iraq Abstract— Different slot structures have been widely used in numerous designs to produce antennas with enhanced bandwidths. In this paper, a printed slot antenna has been introduced as a candidate for use in the multi-band wireless communication applications. The antenna slot structure has a rectangular shape with its width, from the side of feed, has been modified in the form of Koch fractal curve of the second iteration. The antenna has been fed with 50 Ohm mi- crostrip transmission line etched on the reverse side of the substrate. Modeling and performance evaluation of the proposed antenna design have been carried out using a method of moments based EM simulator, IE3D. Simulation results show that the resulting antenna exhibits a multi- resonant behavior making it suitable for a wide variety of multi-band wireless communication applications. The first resonant band, centered at 2.58 GHz, extends from 2.40 to 2.89 GHz. This band covers the 2.4 GHz WLAN band (frequency range 2.4–2.483 GHz) and the 2.5 GHz mobile WiMAX operating band (frequency range 2.5–2.7 GHz). The second resonant band, centered at 4.03 GHz, extends from 3.40 to 4.50 GHz. This band covers the 3.5 GHz mobile WiMAX oper- ating band (frequency range 3.4–3.6 GHz). While the third resonant band centered at 5.74 GHz, extends from 5.42 to 6.18 GHz. This band covers the U-NII mid-band (frequency range 5.47– 5.725 GHz) and U-NII high-band (frequency range 5.725–5.875 GHz). Parametric study has been carried out to explore the effect of varying the antenna feed line length on its performance. 1. INTRODUCTION The term fractal, which means broken or irregular fragments, was originally coined by Mandel- brot [1] to describe a family of complex shapes that possess an inherent self-similarity in their geometrical structures. A wide variety of applications for fractal has been found in many areas of science and engineering. One such area is the fractal electrodynamics [2, 3] in which fractal geometry is combined with electromagnetic theory for the purpose of investigating a new class of radiation, propagation, and scattering problems. One of the most promising areas of fractal electrodynamics research is its application to the antenna theory and design. Another prominent benefit that has been derived from using fractal geometries has been to design antenna with mul- tiple resonances [3, 4]. Fractals are complex geometric shapes that repeat themselves, and are thus self similar. Because of the self-similarity of the geometry due to the iterative generating process, the multiple scales of the recurring geometry resonate at different frequency bands. Hilbert, Peano, and Gosper space-filling curves have attracted the researchers to achieve antenna miniaturization with multiple resonances [5–14]. Many Hilbert fractal-based structures have been proposed to produce printed and microstrip dipole and monopole antennas with compact size and multiband performance for different applications [5–11]. Peano space-filling curves have also drawn the interest of many research groups, where different aspects of many Peano fractal antennas have been reported [11–14]. Gosper space-filling curve has been used to model reduced size multiband antenna [15]. Moreover, structures based on these space-filling geometries have been successfully used in different ways to form parts (or the whole) of the ground plane of miniature and multiband antennas [16]. It is worth to note that, in the majority of the published works, the different types of space-filling curves have been used to model dipole and monopole antennas. Slot antennas based on space-filling curves have drawn less attention from antenna designers; to name a few [10,17–20]. In this paper, a printed slot antenna structure has been introduced as a candidate for use in the modern compact and multi-function communication systems. The proposed structure has a rectangular slot shape with one of its sides has been modified to be in the form of the second iteration Koch fractal curve. The proposed antenna is expected to possess a considerable compact size owing to the space filling property of the Koch fractal curve. 2. THE PROPOSED ANTENNA STRUCTURE The starting pattern for the proposed antenna as a fractal is the straight line segment, Figure 1(a). From this starting pattern, this straight line segment is replaced by the generator shown in Fig- ure 1(b). To demonstrate the process, the first three iteration steps are shown in Figure 1.