Modeling a varactor diode in ADS

I would like to model the nonlinear behavior of a varactor diode in ADS. I am trying to validate that the circuit model developed by Skyworks and presented here: http://www.skyworksinc.com/uploads/d...ts/200315B.pdf works with a time varying bias signal. I want the junction capacitance to be a function of the bias vd over the entire varactor (not just the junction). Can I use a SDD1P component and reference a voltage vd that is outside the component? How would you accurately model a varactor diode? Thanks!