Small Printed Ultra Wideband Antenna with Coupled Slot Yusnita Rahayu #1 , Tharek A. Rahman 2 , Razali Ngah 2 , Peter S. Hall 3 #1 Faculty of Mechanical Engineering, Universiti Malaysia Pahang, Kuantan, Malaysia 2 Wireless Communication Centre (WCC), Faculty of Electrical Engineering Universiti Teknologi Malaysia, Johor Bahru, Malaysia 3 Department of Electronic, Electrical and Computer Engineering University of Birmingham Edgbaston Birmingham, B15 2TT United Kingdom 1 vannebula2001@yahoo.com Abstract— This paper presents a small printed ultra wideband (UWB) antenna with a coupled slot. This proposed antenna uses coupled L and U slots to broaden the bandwidth. A truncated ground plane is designed to control the antenna’s impedance matching. Both slots were designed by investigating the behaviour of the current distribution of the patch antenna. It is shown that by proper design of the slot width and length of those coupled slots, without degrading their performance, a broad bandwidth can be obtained. The antenna’s dimension is 30 mm x 30 mm and fed by microstrip line. Both simulated and measured results have shown a good return loss with respect to -10 dB and nearly omni-directional pattern over 2.5 GHz to 10.1 GHz. Thus, this proposed antenna is as potential candidate in UWB application. I. INTRODUCTION In recent years, UWB antennas have experienced many significant developments and have been getting more and more popular due to its simple structure, low cost, low power consumption, wide bandwidth and high data transmission rate. UWB antennas have to be able to transmit pulses as accurately and efficiently as possible. The spectrum allocated certainly requires transmitters and receivers with wideband antennas. The main challenge in UWB antenna design is achieving the extremely wide impedance bandwidth while still maintaining high radiation efficiency. By definition, an UWB antenna must be operable over the entire 3.1 GHz to 10.6 GHz frequency range [1]. Therefore, the UWB antenna must achieve almost a decade of impedance bandwidth, spanning 7.5 GHz. Today the state of the art of UWB antenna focuses in the microstrip, slot and planar monopole antennas with different matching techniques to improve the bandwidth ratio without loss of its radiation pattern properties [2]. Many research papers on monopole UWB antennas have been reported in many literatures [3-6]. In this paper, a small printed UWB antenna is presented. The proposed antenna consists of a coupled slot, L and U, with truncated ground plane. The slot’s shape is designed by studying the current distribution which will give input impedance improvement. The truncated ground plane is used to control the antenna’s impedance matching. Both simulated and measured results have shown a good return loss over the entire bandwidth, the effect of each slot to the current distribution will be discussed as well. II. ANTENNA DESIGN Fig. 1 shows the proposed antenna structure printed on the FR4 substrate of  r = 4.6. The pentagonal antenna is vertically installed above a ground plane (l grd ) of 11 mm. The optimum feed gap (h) to the ground plane is found to be 1.5 mm. The dimension of substrate is chosen to be 30 x 30 mm 2 (W sub x L sub ) in this study. The antenna has a pentagonal shape with a width (w) of 15 mm and a length (l) of 12 mm. This shape is variation of the rectangular shape with bevel techniques. The slot size of the proposed antenna is listed in Table 1. The slot width is 0.5 mm in order to improve the bandwidth above 10 GHz. (a) (b) Fig. 1 (a) Geometry and coordinate system of the UWB coupled slot antenna, (b) Photograph of the coupled slot antenna 978-1-4244-2721-5/09/$25.00 ©2009 IEEE 2009 Loughborough Antennas & Propagation Conference 16-17 November 2009, Loughborough, UK 397