This study reports an experimental study of the system fidelity factor (SFF) of ultra-wideband wireless body area network antennas in an on-body environment. This study also investigates the influence in the SFF because of the antenna polarisation with respect to the body. For this purpose, two antennas having different polarisations are compared: a mono-cone antenna with the polarisation perpendicular to the wearer and a printed monopole with the polarisation either parallel or perpendicular to the wearer. A phantom made of pork meat was considered as a model for the wearer's body, and five different communication scenarios involving each pair of antennas were considered. On-body experimental results show that the time-domain behaviour of the transmission is better for two different antenna types having the same polarisation, but, more importantly, that the SFF (and thus the time-domain fidelity of the signal) is better for a link having a polarisation perpendicular to the body.