A radar system coherently combines signals from independent upper- and lower-sub-band radars, mutually coheres the sub-band radar signals, and performs model fitting and parameter estimation to obtain ultra-wideband data signatures from a target. Signal processing models are used to compensate for potential lack of mutual coherence between the various sub-bands. An ultra-wideband signal model is fitted to the sparse sub-band measurements to accurately characterize ultra-wideband target scattering and provide for meaningful interpolations or extrapolations outside of the measurement sub-bands.