This paper is a further study on the performances of planar UWB monopole an- tennas using a radiator of difierent shapes such as triangle, rectangle, square, circle, annual ring, ellipse (both horizontal and vertical), pentagon and hexagon, for body-centric wireless networks. The planar antennas consist of a radiator and a microstrip-feed line on one side of the substrate and a ground plane on the other side. Previous simulation studies showed that the elliptical and hexagonal antennas appeared to have the best performances in terms of bandwidth, gain, e-- ciency and radiation pattern. Studies using measurements of these two antennas on a liquid-body phantom are presented in this paper. Results show that the elliptical antenna achieves a wide impedance bandwidth of 3.1{12GHz, an average peak gain of nearly 2.3dBi and good radiation patterns, making it a good candidate for UWB body-centric wireless networks. 1. INTRODUCTION Ultra-wideband (UWB) technology (1), with the advantages of low cost, low complexity, low spectral power density, high precision ranging, low interference and extremely high data rates, has attracted much attention (2{9). One of the most promising areas in UWB applications is body-centric wireless networks where various sensors are connected together by UWB devices which have to be low power, low-proflle and unobtrusive to the human body (10,11). Due to the presence of human body, the design of UWB antennas for body-centric wireless networks is complicated. Several fundamental requirements such as wide impedance bandwidth, small size and low proflle, good on- body propagation and radiation characteristics in the proximity of the body have to be fulfllled (10{ 15). The studies on planar UWB monopole antennas using a radiator of difierent shapes such as rectangle, square, circle, ellipse, pentagon and hexagon, for body-centric wireless networks using computer simulation were carried out in (16). Results showed that among all proposed antennas studied the elliptical and hexagonal antennas had the best performances for UWB body-centric wireless networks In this paper, further studies are carried out on the elliptical and hexagonal antennas by using measurements. The antennas are fabricated using FR-4 substrate placed on a body model and measured inside an echoic chamber. Results show that the antenna with an elliptical radiator appears to be the best choice for UWB body-centric wireless networks.
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