L-band LNA discussion

Dear microwave colleagues,

the specs are: 1.6-1.7 GHz, NF<0.75 dB, G>=30 dB (2-stage amp), absolute stability within the whole frequency range of the devices. It will be used for a weather-satellite reception with a 1.5m dia dish.

The circuit should be a discrete-design two-stage amplifier. As a first stage an Avago ATF-58143 is a very good selection. Suggest your parts if more suitable.

ATF-58143 needs positive-only voltages, offers quite good noise figure, but stability is a problem.

Any ideas, comments, suggestions, etc?

This was discussed so many times on this forum. K factor is not accurate for a multi stage amplifier.

If it's so, how the stability factor of a multistage amplifier is simulated or predicted ?

K-factor is based on S parameters. Nobody says that the multistage k-fact stability cannot be simulated. Is just not so accurate compared to a single stage.

What is your proof ? Because K-Factor is used in every textbooks as the figure of stability and no one mentioned about that is limited to single stage amplifiers and it can not be so accurate in multistage amplifiers.

And how the overall stability is found of a amplifier chain ? Since we're not able to find Hurwitz polynoms to define the stability of LTI system, an AC simulation should be done to find gain and phase margin ?

What is your method ?

Here we speak about K-factor to predict stability, and no other methods.
Not only me, but I met a lot of experienced RF engineers which found that K-factor is not the best option for accurate multistage stability prediction. Can give a rough indicator where the design stands, but don't bet all the money on it.

If anybody finds this interesting, I've achieved NF=0.58dB with G=26dB @ 1.6GHz. PM for more.

I am guessing this is not typical MOSFET LNA because that is a low noise figure.

Oh I see it is HEMT, which I am not so familiar. What did you do to create your design? Just impedance match the input and outputs and pick a high gm bias point?