Planar Monopoles with Different Radiator Shapes for UWB Body-Centric Wireless Communications

This paper presents a study on the performances of a group of planar monopoles using radiators of different shapes, such as triangle, rectangle, square, annual ring, circle, horizontal ellipse, vertical ellipse, pentagon, and hexagon, for ultra-wideband (UWB) body-centric wireless communications. The planar monopoles have the radiators with microstrip-fed line printed on one side of the substrate and a ground plane on the other side. Simulation studies show that, among these monopoles, the horizontal elliptical, vertical elliptical, and hexagonal monopoles have better overall performances in terms of bandwidth, gain, efficiency, and radiation pattern in free space. A solid-body phantom mimicking human tissue is used for studies of these three monopoles for body-centric communications. Simulated and measured results of these monopoles on the phantom show that the horizontal elliptical monopole achieves the widest impedance bandwidths, highest average peak gain and efficiency, least path loss, best fidelity, and good radiation pattern, making it a good candidate for UWB body-centric wireless communications. 1. Introduction Ultra-wideband (UWB) technology [1], due to 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 [2–6]. One of the most promising areas in UWB applications is body-centric wireless communications where various sensors are connected together by UWB devices which have to be low power, low profile, and unobtrusive to the human body [7, 8]. However, the electrical properties of human body make the design of UWB antennas for body-centric wireless communications very complicated. Several fundamental requirements such as wide impedance bandwidth, small size and low profile, good on-body propagation, high front-to-back ratio, and good radiation characteristics in the proximity of the body need to be fulfilled [7–12]. Some practical applications of body-centric wireless communications systems have been studied. In [13], a body-centric wireless communication equipment, SenseWear Pro2 Armband, was studied for health monitoring. It was worn on the arms for up to two weeks continuously and allowed calculation of energy expenditure and quantification of metabolic physical activity. In [14], a wearable textile antenna integrated in protective garments for firefighters was presented. Comparison of different UWB antennas for body communications has been studied before since 2005 [9, 15–17]. In [10], two types of UWB antennas, printed