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NF of LNA with Duplex filter

Question asked by Leyo on Apr 25, 2007
Latest reply on Apr 26, 2007 by Leyo

I have LNA with 1dB NF when terminated with 50 ohms. There is source mathcing circuits so that 1dB of NF is achieved. The Input return loss  of LNA is 15dB.

I want to calculate the NF of a cascade of this LNA and filter before the LNA. Filter has IL  of 1dB, Output RL of 15 dB.

There will be a  worstcase mismatch loss of of -0.279 to +0.27 dB between filter  output and LNA.

So total NF = 1dB(Filter IL)+0.279(Mismatch loss)+1dB(LNA NF)=2.79 dB.

Is this calculation correct ?.This  calculation doesn't include the change in NF of LNA beacuse of different source than 50 ohms when filter is connected. How to include this also in the calculaations?