reading Zi from s parameters

hi.i'm going to match rd15hvf1 for 75-110MHz(mitsubishi mos transistor). "Zi" is given for 175MHz in datasheet . but it's different with "Zin" i read with ads or awr.how can i reach "Zi"given in datasheet? can i match tarnsistor with "Zin" read with ads? and can i simulate all my circuits with s2p file or should i simulate input and output matching with good s11 or s22 seperately? thank you

S parameters are measured with a 50 ohm at the other port. For instance, S11 is measured with a 50 ohm load on port 2. But a transistor is not going to be driving a 50 ohm load....instead there is probably a matching network on both the input AND output side of the device. So the device does not see 50 ohms, and the apparent "S" parameters will change. They are probably just publishing the desired Zin when the recommended matching network on port 2 is installed.

hi, thank you for your answer. i've got another question( if it's ok):
should we simulate input AND output matching network seprately to get good s11 and s22?(is it enough)
or is it possible to simulate matching input AND s2p file of transistor AND output matching network together?(when i simulate in the second format, results are not reasonable), i whould be thankful if you help me

you can do them one at a time to start off, but eventually you need to optimize them both at the same time to get the final results you need. Otherwise, one side will always be a little off.