Bandwidth Enhancement of UWB Microstrip Antennas with Ground Plane Modifications Niruth Prombutr 1 , # Phumin Kirawanich 1 , Prayoot Akkaraekthalin 2 1 Department of Electrical Engineering, Mahidol University, Nakhon Pathom 73170 Thailand, egphumin@staff2.mahidol.ac.th 2 Department of Electrical Engineering, King Mongkut’s Institute of Technology North Bangkok, Bangkok, 10800 Thailand 1. Introduction Ultra-wideband (UWB) technology has been regarded as one of the most promising wireless technologies that have a capability of revolutionizing high data rate transmission. Since released by the FCC of UWB wireless communication bandwidth of 7.5 GHz (3.1 - 10.6 GHz), a number of new developed techniques to support high data rate wireless communication for the next generation technologies have been rapidly increasing. Basically, the maximum achievable data rate or capacity is related to the bandwidth and the signal-to-noise ratio through Shannon-Hartley criterion [1]. Since the transmission power can not be readily increased due to the size of portable devices, a large frequency bandwidth seems to be the proper solution to achieve a high data rate. Due to the low UWB performances offered by wire antennas, a large number of patch antennas have been introduced to give superior performances for a variety of UWB applications. Among several shapes of patch antennas, circular or elliptic discs provide the wider impedance bandwidth compared with square plates [2]. Due to their simple geometries and the ease of fabrication, several methods to increase the impedance bandwidth including the use of beveling, semi-circular base, and cutting notches at the bottom. The aim of such techniques was to adjust the electrical distance between the bottom part of the planar monopole antenna and the ground plane so that the coupling between these structures can be tuned for wider impedance bandwidths. In this paper, we report the techniques to enhance a bandwidth using a microstrip-fed circular disc planar monopole. We modified the ground plane by superimposing the uses of diagonal cuts at the corners, rectangular slots, and T-shaped cuts where each of these techniques have been previously reported [3]-[5]. The simulation analysis of our proposed antenna was compared with measurement counterpart. Following this introduction, we have organized the rest of the paper as follows. The detail of antenna design and preliminary results from simulations are described in Section 2. Section 3 discusses the experimental results. This work concludes in Section 4. 2. Antenna Ground Plane Design The geometries of the planar monopole antennas in our study are shown in Fig. 1. We used the microstrip structure due to many advantages, such as compact in both size and weight, and inexpensive. Our objectives were to modify the structure by incorporating several techniques to improve the bandwidth. The antenna configuration in Fig. 1(a) was first used as a baseline for parametric study. The circular disc planar monopole was fabricated on a 3 cm × 5.1 cm × 0.16 cm FR-4 board (ε r = 4.4) with a feed line, and a finite ground plane. The radius R of the circular disc, the width w g of the microstrip feed line, the ground plane dimensions L and W, and the distance between the bottom part of the disc and the top part of the ground plane h were already optimized in our previous study [6]. The ground plane modifications, which are the diagonal cuts at the corners, rectangular slots, and T-shaped cuts, are our main design in this paper. The preliminary simulation results determined using the commercial high frequency structure simulator (IE3D) [7]. The 2009 International Symposium on Antennas and Propagation (ISAP 2009) October 20-23, 2009, Bangkok, THAILAND - 484 -