International Journal of Computer Applications (0975 – 8887) Volume 68– No.3, April 2013 26 X – Band Fractal Microstrip Antenna for Wireless Application B. Hephzibah Lincy M.E Communication Systems GKM College of Engineering and Technology Chennai – 63, India. A. Srinivasan Associate Professor/ECE GKM College of Engineering and Technology Chennai – 63, India. B.Rajalakshmi Assistant Professor/ECE GKM College of Engineering and Technology Chennai – 63, India. ABSTRACT Wideband application put a new demand on antennas pertaining to size, gain, efficiency, bandwidth and more. This paper presents the design and analysis of fractal antenna which uses the self similarity property of fractal geometry. This unique property is exploited to develop antenna elements that are wideband and compact possessing highly desirable properties. The presented antenna is circle inscribed octagon shaped. Simulation results show that the antenna can be used in X band frequency range exhibiting wideband properties. Radiation pattern and gain characteristics are also analysed. Key words Fractals, Wide Band, Fractal Microstrip Patch Antenna, X band. 1. INTRODUCTION Modern developments in communication systems require antennas with wider bandwidth and smaller dimensions. Demand for such antennas which are smaller in size, low fabrication complexity and low cost has increased in military as well as commercial applications. For conventional antenna if size is less than a quarter wavelength then radiation bandwidth and efficiency is reduced [3]. This problem is overcome by using fractal geometry in designing antennas. Fractals have self similar shapes and space filling properties that can be subdivided into parts. This property makes the fractal antenna compact and wideband. The different fractal elements of the antenna make it to have different resonances. The presence of discontinuities in the geometry increases the bandwidth and radiation properties of antenna. It also has long electrical lengths that fit into a compact size [8][5]. In this paper a new fractal geometry which is circle in octagon shaped is designed. Antenna parameters for operating frequency of 10GHz, in X band frequency ranges are analysed and found to exhibit multiple bands. Simulation is done in Ansoft HFSS software and the results are compared. 2. DESIGN APPROACH Fractal microstrip patch antenna is designed based on iterative method [8]. Dimension of each iteration is different. A number of iterations can be performed but considering fractal antenna’s compactness only three iterations are performed. Also, in higher iterations there is no significant change in antenna properties [1]. The interior and exterior radius of the octagon, as shown in figure 1, is given by                     Where, a – side of the octagon   – External radius   – Internal radius Figure 1: Geometry of Octagonal Sub array The array factor of the fractal antenna is given by [4],         Where,  - Scaling factor P - Level of iteration  – Array Factor Associated with Generating Array The radius of the circle that is subtracted from the octagon is the interior radius of the octagon. This is repeated till the third iteration is obtained. The side of the first iterative octagon is a=14.7mm and radius of the first inner circle subtracted is r=17.8mm. The three iterative patterns with CPW feed are shown in figure 2.    