We present a shot-noise based model for a large family of ultrawide bandwidth (UWB) signals. These include time-hopping and direct-sequence signaling with pulse position, interval and amplitude modulations. Each specific signal is constructed by adding features to a basic model in a modular, simple, and tractable way. Our work unifies the contributions scattered in the literature and provides a general approach that allows various extensions of previous works. The exact power spectrum is then evaluated using shot-noise spectral theory, which provides a simpler, systematic, and rigorous approach to the spectra evaluation of complex UWB signals. The strength of our methodology is that different features of the model contribute clearly and separately in the resulting spectral expressions.