SLOTTED ULTRA WIDEBAND ANTENNA FOR BANDWIDTH ENHANCEMENT Yusnita Rahayu 1 , Tharek A. Rahman 2 , Razali Ngah 3 , Peter S. Hall 4 1,2,3 Wireless Communication Centre (WCC), Faculty of Electrical Engineering Universiti Teknologi Malaysia, Johor Bahru, Malaysia (1) vannebula2001@yahoo.com (2) tharek@fke.utm.my (3) razalin@fke.utm.my 4 Department of Electronic, Electrical and Computer Engineering University of Birmingham Edgbaston Birmingham, B15 2TT United Kingdom (4) p.s.hall@bham.ac.uk Abstract, In choosing an antenna topology for ultra wideband (UWB) design, several factors must be taken into account including physical profile, compatibility, impedance bandwidth, radiation efficiency, and radiation pattern. In this paper, a small compact T slots UWB antenna is presented. It originates from conventional rectangular monopole and is realized by adding T slots for both patch and feeding strip. The wideband behaviour is due to the fact that the currents along the edges of the slots introduce an additional resonance, which, in conjunction with the resonance of the main patch, produce an overall broadband frequency response characteristic. The slots also appear to introduce a capacitive reactance which counteracts the inductive reactance of the feed. Thus, the bandwidth broadening comes from the patch and T-slots, coupled together to form two resonances. The effect of current distributions of the T slots was simulated by using Zeland FDTD. The measured return loss of this proposed antenna is also presented as well. 1. Introduction Over the past few years, considerable research efforts have been put into the design of UWB antennas and systems for communications. Accordingly, many techniques to broaden the impedance bandwidth of small antennas and to optimize the characteristics of broadband antennas have been widely investigated in many published papers as listed in [1–17]. Some examples of the techniques used to improve the impedance bandwidth of the planar monopole antenna include the use of beveling technique [1], [2], [11], semi-circular base [13], cutting notches at bottom [6], [12], an offset feeding [1], [2], [15], a shorting pin [1], [16], and a dual/triple feed [1], [8], [10], [12], [17], magnetic coupling [3], folded-plate [5], [9], hidden stripline feed [14]. The radiators may be slotted to improve the impedance matching, especially at higher frequency [1], [4]. Planar monopole antennas are good candidates owing to their wide impedance bandwidth, omni-directional radiation pattern, compact and simple structure, low cost and ease of construction. In this paper, a small compact T slots UWB antenna is presented. To design this UWB antenna, three techniques have been applied to the proposed antenna: (i) two steps of notches placed at the two lower corners of the patch, (ii) a partial ground plane and (iii) T slots, which can lead to a good impedance matching. By selecting these parameters, the proposed antenna can be tuned to operate in the 3.1–10.6 GHz frequency range. Both simulation and experimental results are discussed as well. The simulation results in this paper are obtained from Zeland simulation, which are based on the FDTD method. 2. Antenna Design Fig. 1(a) and Fig.1(b) show the geometry and photograph of the proposed UWB antenna, respectively. As shown in Fig.1(a), the antenna has a compact dimension of 30 mm x 30 mm (W sub x L sub ), designed on FR4 substrate with thickness of 1.6 mm and relative dielectric constant (ε r ) of 4.7. The radiator is fed by a microstrip line of 3 mm width (w f ). On the front surface of the substrate, a rectangular patch with size of 15 mm x 12 mm (w x l) is printed. The distance of h between the rectangular patch to ground plane printed on the back surface substrate is 1 mm, and the length (l grd ) of truncated ground plane of 11 mm. The excitation is a 50 Ω microstrip line printed on the partial grounded substrate. 449 2008 Loughborough Antennas & Propagation Conference 17-18 March 2008, Loughborough, UK 978-1-4244-1894-7/08/$25.00 ©2008 IEEE