Progress In Electromagnetics Research Symposium Proceedings, Moscow, Russia, August 19–23, 2012 613 An Ultra-wideband Printed Monopole Antenna with a Fractal Based Reduced Ground Plane Jawad K. Ali, Ali J. Salim, Ali I. Hammoodi, and Hussam Alsaedi Microwave Research Group, Department of Electrical Engineering University of Technology, Baghdad, Iraq Abstract— Recently, the ultra-wideband (UWB) systems have attracted much attention be- cause of its advantages including high speed data, small size, low cost, and low complexity. Consequently, the UWB antenna has received an increased attention due to its impedance band- width, simple structure and omni-directional radiation pattern. In this paper, the effects of the ground plane of a printed monopole UWB antenna, fed with a 50 Ω microstrip line, have been investigated. A Koch fractal based ground plane structure has been proposed as a means to enhance the UWB antenna performance. Different ground plane structures and feeding methods have been applied to a notched band monopole antenna structure that is a nearly square with embedded E-shaped slot. The proposed antenna has been supposed to be etched using a substrate with relative permittivity of 4.6 and thickness of 1.6 mm. Modeling and performance evaluation of the presented antenna designs have been carried out using a method of moments based EM simulator, IE3D. Simulation results have shown that the antenna with Koch based ground plane and asymmetrical feed offers larger fractional bandwidth of about 124%. By this increment in the antenna bandwidth, it is expected that by suitable dimension scaling of the enhanced bandwidth UWB antenna, many communication services below 3.1 GHz could be integrated with the UWB systems. 1. INTRODUCTION Ultra-wideband (UWB) communication system is attracting more and more attention because of its advantages such as low power consumption, high data rate transmissions as in the multimedia communications, robustness against jamming, high degree of reliability etc. [1]. Consequently, an increased interest has been reported to the UWB antenna design. For portable devices, an additional challenge is encountered; the antenna has to be miniaturized. The printed UWB antenna has been found to be a good option because it can be easily embedded into wireless devices or integrated with other RF circuits [2]. In 2002, the Federal Communication Commission (FCC) officially released the regulations for UWB technology with allocated spectrum from 3.1 to 10.6 GHz for unlicensed UWB indoor medical, measurement and communication applications [3]. Since then, intensive research work has been devoted to the UWB antenna design. Regarding the purpose of reducing the potential interference between the UWB system and others operating at 5/6 GHz, the antennas reported in the literature can be classified into three categories. The first one includes antenna that are not characterized with a band notch in their return loss, or VSWR, responses [2–5]. In this context, microstrip fed printed monopole antennas having radiators with E-shape [2], swan-like shape patch with reduced ground plane [3], circular shape monopole with trapezoid shape ground [4], and octagon shape [5], are presented for UWB applications. In the other hand, the CPW feed line has been also used for UWB antennas with various possible slotted patch structures [6, 7]. The UWB antennas of the second category are characterized with a single 5/6 GHz band notch in their return loss responses [8–12]. Again, almost similar techniques have been adopted to achieve the UWB impedance bandwidth. Slotted elements of various shapes have been added to create the required notch in the antenna response. In addition, the use of the electromagnetic-bandgap (EBG) structure is proven to be effective create the required band notched response [13]. Elliptical monopoles with CPW feeds were fabricated on liquid crystal polymer (LCP) with reconfigurable 5/6 GHz band-notch characteristics has been presented in [14]. In the third category, antennas are characterized with two band notches in their return loss, or VSWR, responses [15–20]. In this paper, the effects of the ground plane of a printed monopole UWB antenna have been investigated. In an attempt to enhance the UWB antenna performance a new fractal based ground plane structure has been proposed. Many ground plane structures and feeding methods have been applied to a notched band monopole antenna structure that is a nearly square with E-shaped slot embedded in it. It is expected that by suitable dimension scaling of the enhanced bandwidth UWB antenna, many communication services below 3.1 GHz could be integrated with the UWB systems, as recently reported in [21–23].