The aim of this article is to present a simple but robust model characterizing the frequency dependent transfer function of an in-vehicle ultra-wide-band channel. A large number of transfer functions spanning the ultra-wide-band (3 GHz to 11 GHz) are recorded inside the passenger compartment of a four seated sedan car. It is found that the complex transfer function can be decomposed into two terms, the first one being a real valued long term trend that characterizes frequency dependency with a power law, and the second term forms a complex correlative discrete series which may be represented via an autoregressive model. An exhaustive simulation framework is laid out based on empirical equations characterizing trend parameters and autoregressive process coefficients. The simulation of the transfer function is straightforward as it involves only a handful of variables, yet it is in good agreement with the actual measured data. The proposed model is further validated by comparing different channel parameters, such as coherence bandwidth, power delay profile, and root mean square delay spread, obtained from the raw and the synthetic data sets. It is also shown how the model can be compared with existing timedomain Saleh-Valenzuela influenced models and the related IEEE standards.