Impedance behaviour of planar UWB antennas in the vicinity of a dispersive tissue model

In Ultra Wideband (UWB) Wireless Body Area Network (WBAN) systems, the propagation environment is comprising free space and lossy medium (human body tissues), which have a very strong effect on the antenna operation. This paper investigates the UWB antenna-body tissues interaction in terms of the reflection coefficient and input impedance behavior through the range of 0-30 mm away from the body surface. Planar UWB antennas are exploited in the investigations. A layered tissue model based on the Debye's dispersion model for UWB frequencies is used in simulations. Observations are considered in relation to the antenna near-field regions and the size, i.e., the boundary distance of antenna's reactive near-field is noticed to be the important factor in the evaluation of the shortest antenna-body operating distance.