IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009 637 PIFA Bandwidth Enhancement by Changing the Widths of Feed and Shorting Plates Hassan Tariq Chattha, Yi Huang, and Yang Lu Abstract—The ultrawideband (UWB) systems require antennas having a very broad bandwidth. The planar inverted-F antenna (PIFA) is widely used in mobile systems due to its excellent perfor- mance. However, its bandwidth is very limited. This letter is aimed at addressing this problem by investigating the effects of changing the widths of the feed plate and shorting plate on the impedance bandwidth. It is shown that a PIFA with a much wider bandwidth (up to 65%) than previously reported can be achieved by opti- mizing the widths of the feed and shorting plates. Simulated and measured results are provided to verify the conclusion. Index Terms—Antennas, input impedance bandwidth, planar antennas, planar inverted-F antenna (PIFA). I. INTRODUCTION T HE inverted-F antenna is evolved from a quarter-wave- length monopole antenna and is now widely used in mo- bile and portable applications due to its simple design, light- weight, low cost, conformal nature, attractive radiation pattern, and reliable performance [1]–[4]. The planar inverted-F antenna (PIFA) is an extension of the wire inverted-F antenna in which the wire is replaced with a plate in order to increase the bandwidth. However, PIFA is still generally considered a narrowband antenna, and a significant amount of effort has been made to broaden its bandwidth. It was shown that the height [5], shorting plate width [6], and mean- dered shorting strip [7] can be used to increase the bandwidth, but in these papers either the impedance bandwidth is not very broad or they are not practically implemental. Feik et al. have shown that diversely shaped feed plates can be used to increase the impedance bandwidth (up to about 25% fractional band- width), but they did not investigate the size of feed plate and have used a very large shorting plate [8]. This study, as part of a comprehensive study of the PIFA, investigates the effect of changing both the rectangular feed width and shorting plate width on the impedance bandwidth of the antenna. It is found that a much wider bandwidth than previously reported can be achieved, and the new PIFA may be regarded as a wideband [or even ultrawideband (UWB)] antenna if the correct widths of the feed and shorting plate are chosen. The proposed approach is a Manuscript received January 11, 2009; revised February 27, 2009. First pub- lished May 19, 2009; current version published July 09, 2009. The authors are with the Department of Electrical Engineering & Electronics, University of Liverpool, Liverpool L69 3GJ, U.K. (e-mail: h.chattha@liv.ac.uk, Yi.Huang@ieee.org, luyang@liv.ac.uk). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LAWP.2009.2023251 Fig. 1. Geometry of PIFA. Fig. 2. PIFA with SMA connector. simple and more practical way of getting the maximum impedance bandwidth than the previously reported methods. II. ANTENNA CONFIGURATION The configuration of a typical PIFA shown in Fig. 1 is chosen for this study. The radiating top plate has dimensions of , and ground plane dimensions are . There is a FR4 sub- strate of thickness mm and a relative dielectric constant of 4.4 between the rectangular ground plane and feed plate. The antenna height is , and the space between the top plate and the substrate is filled with air (free-space). The model in Fig. 1 is made purely for the ease of construction in our lab. In practice, a substrate is generally just underneath the top plate, but this will make the top plate too heavy to be supported by the shorting and feeding plates. For production, the antenna size can be reduced by loading a dielectric between the ground and top radiating plate, which will make the antenna more robust. The shorting 1536-1225/$25.00 © 2009 IEEE