The WSSUS channel model has provided a useful tool for modeling random time variant linear channels in the four decades since its introduction. However, with the advent of UWB (Ultra Wideband) communications, it is necessary to replace this model which is valid for Narrowband (NB) channels. This paper develops such a replacement. The development is based upon the tapped delay line model of a linear time- variant channel, which is valid for any ratio of bandwidth to carrier frequency. For simplicity, the analysis assumes a dense multipath environment such as may be experienced in outdoor and indoor urban environments. The thrust of this study is to derive an UWB channel model for dense multipath that will allow a meaningful comparative modem performance evaluation rather than to develop a new precise characterization of UWB channels. Such a model should be useful in preparation of UWB communication standards for mobile links.