Improved Performance of UWB Antenna by Substrate Perforation and Slit Notch Wessam Zayd 1 , Alyani Ismail 2 , Maryam Mohad Isa 3 ,Suci Rahmatia 4 1,2,4 Department of Computer and Communication Systems Engineering, 3 Department of Electrical and Electronic Engineering. Faculty of Engineering, Universiti Putra Malaysia, 43400, UPM, Serdang, Selangor, Malaysia 1 wzsiraq@yahoo.com 2 alyani@eng.upm.edu.my 3 misa@eng.upm.edu.my 4 uci_depok@yahoo.com Abstract— In this paper a compact semi elliptical monopole ultra-wideband (UWB) antenna has been presented. A new technique to improve the performance of the antenna by perforation of the substrate with two circular holes was used. This perforation has significant effect to minimize the return loss in addition of using the existing techniques to improve the impedance bandwidth like notching off each of the patch and the ground plane. The simulation results show that the optimized design has an fractional bandwidth of 133% and bandwidth of 10.4 GHz starting from 2.6 GHz to more than 13 GHz with return loss batter than 10 dB and VSWR less than 2 with near Omni-directional radiation pattern over entire this band. The proposed antenna was fabricated. The measured return loss shows a good agreement with the simulation results. Keywords— Monopole antenna, bandwidth enhancement, printed antenna, partial ground plane, Ultra-wideband (UWB) antenna. I. INTRODUCTION UWB is an emerging important technology finding a myriad of nowadays applications. This is due to its excellent immunity to multipath interference and high-speed data rate. Ultra-wideband systems use ultra- wide range of frequencies with very low power to transmit and receive very narrow electromagnetic pulses. Therefore, it would be necessary to design efficient antennas that provide acceptable bandwidth requirements, good radiation efficiency and appropriate radiation patterns throughout the UWB spectrum. In 2002, a 7.5 GHz licence free bandwidth ranging from 3.1 GHz to 10.6 GHz was released by the Federal Communications Commission (FCC) for UWB applications [1]. Since then many methods have been used to widen the bandwidth of printed planar antennas and improve their radiation pattern. These methods include ground plane shaping [3-6], ground plan notches [7, 8], cutting a slot on the monopole antenna [9, 10], two feeding points to excite the antenna [11] and stacked multi resonator patches [12]. Generally, all these mentioned designs can be classified under specific characteristics such as the radiation pattern. For example the antenna design in [3] has Omni-directional radiation performance which is conducive to the communication applications, since Omni-directional radiation pattern provide a high degree of freedom for the receiver /transmitter locations. While in [5], the directional radiation antenna characteristic has a focused beam with high gain are desirable in Microwave Imaging (IM). Ultra-wide band antennas classification can also be based on the feeding methods such as microstrip line [7], coplanar waveguide (CPW) [6] and coaxial feed [12]. In this paper a new technique is used to minimize the return loss of the planar monopole antenna by perforating the substrate in specific locations between the radiating element of the antenna and finite ground plane. (a) (b) Fig. 1 Photograph of the antenna. (a) Top view. (b) Bottom view. II. ANTENNA DESIGN The geometrical configuration for the proposed antenna featuring compact size of 33×33 mm 2 (W × L) is illustrated in Fig. 2 The antenna structure lies in x-y plane and it is symmetric about its midpoint in y-axis direction. The monopole radiator and the microstrip line feeder are fabricated on the same side of the conventional FR4 substrate which has 1.6 mm thickness and relative permittivity of 4.4, while a partial ground plane is located on the opposite side. At the primary design stages, the feeder width (W t ) was calculated using the standard microstrip line formula, in order to achieve 50 Ω characteristics impedance [2]. Proceedings of the 2009 IEEE 9th Malaysia International Conference on Communications 15 -17 December 2009 Kuala Lumpur Malaysia 978-1-4244-5532-4/09/$26.00 ©2009 IEEE 33