Frequency variance of antenna characteristics may result in severe signal distortion in an ultra wideband communications system. We identify the antenna parameters important in the context of propagation and channel modelling, and analyse their variation with frequency. The group delay, VSWR, impedance and radiation pattern of omni-directional UWB antennas are studied over a range of frequencies. We propose a spatio-spectral normalisation scheme to isolate the effect of the antenna from the c...