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Pi Network & S - parameters

Discussion in 'Electronic Basics' started by [email protected], Dec 16, 2004.

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  1. Guest


    I am new in the RF field and I have a question regarding Pi Networks
    and S parameters.

    I was recently reading an article about Pi networks and it uses in RF.
    I am confused about a couple of things. The article said the k=1/S21,
    where k is the attenuation constant. How do you derive this relation
    between k and S21. I know that k=10^(A/20), where A is the value of
    attenuation, does it have something to do with this?

    My second question is, the article says that the load reflection
    coefficient gammaL=1/k^2. How do I derive this?

  2. I read in that wrote (in
    No, that equation converts between A in decibels and k as a pure number.

    S21 is the forward 'gain' (a number less than 1 for a passive network),
    so the attenuation coefficient is obviously its reciprocal.
    You will find the answer on the pages up to page 17 of the document:

    Remember that in general s21 is a complex number (there is phase-shift
    through the network) and that s21 = 1/k.
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