Polarization behaviour of on-body communication channels at 2.45 GHz

Abstract

The advent of body worn devices and the use of them for a wide range of applications, from entertainment to military purposes, indicate the need to investigate to the behaviour of antennas and wave propagation on the body in depth. Knowledge and understanding and of the on-body channel can lead to the design of efficient antennas and systems for wearable devices. The objective of this work is to identify the propagation mechanism on the body for different polarisation states at 2.45 GHz. In particular, the effect of the body on the antenna performance with normal and parallel polarisation is studied and their capability in launching surface waves is evaluated. It is shown that both vertically and horizontally polarised antennas can launch a transverse magnetic (TM) Norton surface wave mode regardless of their polarisation states. However, horizontally polarised antennas do not launch the wave as strongly as vertically polarised antennas. Also, the change in the far field and near field behaviour of the antennas such as a dipole in proximity to the body is investigated and the observations lead to the design of a novel surface wave parasitic array. This new antenna is directive and can increase the path gain by almost 10 dB compared to other planar antennas. In addition, the effect of the polarization of the antenna on channel path gain is studied and channel cross polarization discrimination is quantified, using both simulation and measurement