Characterizing a discrete MOSFET for RF front-end LNA design

[beeboopbeep]

Hello,

I wanted to get into LNA design for somewhat low-band frequencies (less than ~200 MHz) using simple off the shelf and hobby designed PCBs. However, my background for LNA design is limited to IC design using Cadence and I wanted to find out how I can characterize a discrete MOSFET that can be purchased off the shelf in order to design an LNA using the characterized model on software like ADS. I'm assuming the characterized MOSFET will be in a file providing s-parameters or something similar so that it can directly be placed as a modeled component in something like ADS.

I have access to some of the more expensive lab equipment like network analyzers and such which I plan to learn over the summer and I thought this project may be a great way to learn how to use the equipment.

[Mechatrommer]

S21 plot?

[CFLBob]

If you're trying to design for noise figure, I think what you're looking for is a NF meter or analyzer.  The old HP 8970 or a newer model like the 8973 (now Keysight or Agilent, of course)  If you have access to test equipment for HF/VHF my guess is you probably don't have one. 

It has been a while since I did this, but I think ADS had linear and nonlinear modeling.  Linear was like an S-parameter file with a NF column, and nonlinear was something more like a SPICE model.

Small signal FETs are usually characterized for NF, or at least they give you some information.

[rfeecs]

Look up "noise parameters" or "gamma opt".  Here's an example:
https://www.microwaves101.com/encyclopedias/noise-parameter-extraction-using-source-pull

It requires a quite expensive specialized setup.  Not worth it for 200 MHz.

You might just try using the manufacturer provided SPICE model for simulation.  It might get you in the ball park and close enough to tune on the bench.

[KJDS]

Most FETs designed for low noise use have S-parameters and Noise parameters available.

You'll need both, if you just match to 50 ohms from the S-parameters the noise figure will be terrible.