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does good s11 and s22 affects s21?

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seantan1985

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Hi guys, I using the current reuse technique for my LNA

i manage to calibrate a relatively good s11 and s22 at my operating freq at approximatley 25db however my s21 appears to be at 13db roughly..which according to journal.. it should be 19-20 db.. or maybe better ..as i got a far more better calibrating s11 and s22 compared to the journals..

In my understanding, a good s11 and s22 will bring a better s21.. however, in my case, it doesnt...

can someone tell me my error ?
 

Optimal source and load impedances to get maximum gain generally do not correspond with best S11 and S22.
 

Vfone is correct, google Conjugate Matching.
Also, you will see that a match for optimal Gain will not be the best match
for Max Pout in general.

Cheers
 

Hai i faced the similar problem..... In LNA the gain is the very important term that is s21. so improve that first, and adjust the input and output matching circuit and try to get min -10 dB it is enough. Because ultimately u got the better gain.
 

while simulating, I also felt it is true as u guys said. Is there any theories that you guys can refer to support this ? I need to document the "Why" into facts.. thank you!
 

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