With the desire for ever-increasing data-rates, coupled with the interest in techniques that offer interference mitigation, much research has focused upon ultra wide-band (UWB) systems that can theoretically realise such benefits. In practice, any UWB system will require an antenna to connect it (the radio) to free-space. Through examples of practical measurements from two different UWB antennas, this paper will discuss the characteristics that must be considered when assessing UWB antennas