Design of UWB and multiple-band monopole antennas for body-centric wireless communications

Abstract

This thesis presents the designs of Ultra-wideband (UWB) monopole antennas, textile monopole antennas and transparent UWB textile antennas using planar technology for body-centric wireless communications (BCWC).

A planar antenna designed using offset-fed and slotted ground plane to extend the operating bandwidth for the industrial, scientific and medical (ISM)band and UWB is proposed. Results show that the antenna can achieve a bandwidth from 2.38 to 14.5 GHz with omni-directional radiation patterns in the E-plane. Agroup of nine planar UWB monopole antennas using different radiator shapes such as triangle, rectangle, square, annual ring, circle, horizontal ellipse, vertical ellipse, pentagon and hexagon for BCWC is studied using computer simulation and measurement. Results show that the monopole antenna having a vertical-elliptical-shape radiator has a relatively better performance than other monopole antennas.

Three textile antennas fabricated on fabric materials are studied. The first design is a triple-band textile antenna for wireless-local-area network (WLAN) and worldwide interoperability for microwave access (WiMAX) wireless communication applications. The radiator is composed of two branches and a short stub to generate the resonances at about 2.45, 3.5 and 5.5 GHz, respectively. Simulated and measured results show that the three frequency bands can be set independently. The second design is an UWB antenna consisting of a circular radiator, a tapered feed line and a slotted ground plane. Results show that the antenna can achieve a bandwidth of 3 to 12 GHz. The third design is a compact belt-loop UWB antenna with microstrip-fed. The antenna has a simple elliptical-shaped radiator, a three-step staircase on both sides of the feed line and a slot on the ground plane. It has a very compactsize of 11×40=440 mm2and can still achieve a bandwidth of 3.1 to 12.8 GHz. To emulate the on-body conditions, the two UWB antennas are studied in the bending and crumpling conditions due to the curvature of human body. Results show that both UWB textile antennas have quite stable performances throughout the UWB band.

The two UWB textile antennas are re-designed using a transparent conductive film (TCF)as the radiator and ground plane on fabric substrate. Results show that the measured reflection coefficients of transparent antennas agree well with the simulated results. However, the measured radiation patterns have large discrepancies with the simulated results, which are mainly due to the uncertain electric properties of TCF in radio frequency. Results show that the antennas have a better performance, in terms ofbandwidth, peak gain and radiation efficiency ,than those of other transparent antennas studied before, making our proposed antennas suitable for body-centric wireless communications.