C1971 RF transistir S-parameter

Generally the s-parameters of RF power transistors are not given. Instead, nonlinear spice models are given to design a power amplifier.
Indeed, these of type transistors are dedicated to design single type of application that mentioned in datasheet ( 175MHz RF Power Amplifier) and they are generally not optimized for other applications.
In this case, only application circuit should be implemented.
S-parameter are also extracted from SPICE parameters ( if they are available)..

May be you can find some S parameters file descriptions in ADS, but keep in mind that for a large signal they aren't too useful