• Low noise amplifier (LNA) using CE3520K3
    I've had a lot of experience using FETs like these down in L band to squeeze out the best noise temp possible for atmospheric instrumentation. The issue is these FETs have lots of available gain at low frequencies, so you have to give that gain somewhere else to go. The "easiest" method which I've had success with is using series-C, shunt-L, and maybe another series-L depending, on the input to match gamma_opt, and AC couple that shunt-L to ground with an RF decoupling cap good in your band of interest, and and also terminating it to 50 ohms with a "DC" decoupling cap. The gate voltage is fed through. In my case here, with 10 minutes of futzing around, I get series C of 0.22pF, shunt L of 1.78nH, and RF decoupling of 0.5pF. In this case, it wasn't quite enough for unconditional stability, but adding a 5 ohm series resistor at the drain fixed that. Degrades NFmin by a 0.037 dB, but stabilizes it everywhere. I didn't go so far as adding the drain bias network. The idea is that the FET will see the RF ground through the 0.5pF more than it sees the noise from the termination resistor in your band of interest. Hope that helps.
    Capture1 (29K)


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