RF Input Sensitivity
What source impedance are you driving the IC with?  The complex input impedance of the IC should probably be matched to the source impedance for maximum power transfer, with an appropriate matching network.  Once you have a conjugate match and the input impedance of the IC appears the same as the real part of your source impedance, it will be easy to calculate what voltage drive you need for the appropriate power into the IC.  The easiest way to construct the matching network is probably the Smith chart; take a look here for examples of how to do it.