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S11 and S22 are very close to zero in LNA

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tm.torabi

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Hi,
I tried to have a LNA with the best value of performances for schematic and layout.
The problem is that S11 and S22 are about -2 and -5 in the layout respectively. I know those values should be as negative as possible but I couldn't make a better values for them if I want to keep the gain high enough.

Can you let me know if S11 and S22 mean the design have a big problem? Is there a specific values for them to make sure LNA is working fine?

Thank
 

A answer would be easier if you post a schematic and simulation results.
 

hi,
S11 is reflected wave over incident wave at source and S22 means reflected wave over incident wave at drain.

usually drain output power will be higher due to your LNA amplification. if we have high reflected wave/power at drain, it can damage your device. this is the impact of having bad S11 and S22.

since you are designing LNA, your gain requirement may not be stringent or high enough. thats why you are statisfied with S21 and only asking about S11 and S22. however, you should be worried about life time of your device! get S11 and S22 lower enough and reduce the S21 to the level you want thru bias.

best of luck!
 

Thank you everybody
I found in "RF Microelectronics" book the same thing you mentioned, S11 should be less than -15dB.
 

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