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Smith Chart S11 value

mxm14

I m simulating the following circuit for trying to understand smith chart parameters on virtuoso:

and extracting Z and S parameters:

I hilighted here the value of S11 @30G.

i then plotted S11 on the smith chart:

And i have different values for S11 respect to the previous one:529.6m+j254.9m. I was wondering: how this values are related?

Parents
  • Andrew Beckett
    in reply to mxm14

    You're not plotting the same thing. Your s-parameters in the output pane are the real and imaginary values of the cartesian coordinates of the s-parameters, whereas the marker on the graph is showing the s-parameters transformed onto the Smith chart and are showing the normalised impedance (normalised to 50 Ohms). You can change the markers by using right mouse button over the graph and changing the Smith Chart Properties:

    Then by adding %C, you can then also see the Cartesian coordinates which do match. For more information, look up Smith Charts on Wikipedia, or any number of RF texts (e.g. Fields and Waves in Communications Electronics: Ramp Whinnery and Van Duzer).

  • mxm14
    in reply to Andrew Beckett

    Thank you Andrew!So the values on the Smith chart are related to th eimpedance normalised to 50ohm.

    If i consider the Z11 value @30G I got 

    Shouldn those be related to the Z i read from the smith chart?

Reply
  • mxm14
    in reply to Andrew Beckett

    Thank you Andrew!So the values on the Smith chart are related to th eimpedance normalised to 50ohm.

    If i consider the Z11 value @30G I got 

    Shouldn those be related to the Z i read from the smith chart?

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