Design of Various UWB Small Antennas

Abstract

This dissertation is dedicated to implement of various wideband monopole antennas for ultra-wideband (UWB) application. The proposed antennas are designed on various parametric analysis. Firstly, in order to achieve wideband characteristic of a monopole antenna for UWB application, by using the circular slot and taped ground plane of the antenna, wideband characteristic is obtained. Band-stop mechanisms of the antennas are also analyzed. To further suppress the WLAN and HIPERLAN/2 services, a U-shaped slot and an inverted Y-shaped stub are adopted. Secondly, to increase the lower bandwidth limit, spiral elements are used. To further reduce the size of the antenna, the antenna is miniaturized by half by using the symmetry of the surface current distributions. The proposed antennas feature omnidirectional radiation patterns and good gain flatness. Lastly, a two-element planar antenna for a multiple-input multiple-output (MIMO) is proposed. By adopting two Y-shaped radiators, the antenna provides wideband impedance matching characteristic. To reduce the mutual coupling between two radiators, three stubs are inserted in the ground plane. Furthermore, methods to obtain the MIMO antenna performances are presented and values of the envelope correlation coefficient for the proposed antenna are investigated. In conclusion, the proposed antennas are suitable for UWB applications.