[SOLVED] [Does the cover affects the performance of LNA?]

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dangan1993

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Hi everyone,
Currently, I am designing a three-stage LNA for a radar project and have finished verification without package.
As I put the LNA into the package without a top cover as shown in below left picture, the gain of LNA is similar to case without package.
However, when I put a cover on the top as shown in the below right picture, the DC current reduces and the LNA gain drops by around 10 dB.
Can you please give me some recommendations about this phenomenon?
Thank you in advance!!!

Note that the overall package (including the cover) is connected to the ground plane of the LNA circuit.



 

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If all you do is add the cover and the current changes the indication is it has started to oscillate. Possibly the enclosed space is forming a cavity or some output current is finding its way back to the input.

My first thought is to add a layer of RF absorbent foam to the middle of the cover. Keep the edges clear so they still screw down but cover the inner area with foam to reduce the risk of feedback and reduce the 'Q' if a cavity is being formed.

Brian.
 
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It works well! Thank you very much. ^^
 

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