# Smith Chart - S-Parameters Plot

Discussion in 'Homework Help' started by avins_in, Jul 30, 2011.

1. ### avins_in Thread Starter New Member

Jul 30, 2011
1
0
Hello,

My basic question is with regards to smith charts.
Please look into the link and clarify my doubts regarding plotting of S-Parameters for different frequencies on smith charts.

The link is http://twl.sh/p6qn4L

Thanks

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
If you would care to share the specific nature of your doubts then someone might be able to help.

3. ### narasimhan Member

Dec 3, 2009
72
6
Smith charts are simple to draw even with hand. Refer to some standard books on transmission lines. If you are a beginner then buy a chart and draw using hand. You'll understand it better than using a software.
And as t_n_k said be more specific. You can't expect us to go through the 3 pages.

4. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
The plotting of corresponding points on the Smith Chart given the 's' parameter set isn't trivial - that's why RF CAD packages often make that part easier by doing the transformations for the user.

Only s11 & s22 make any sense plotted on the Smith chart since they are effectively the forward and reverse reflection coefficients for the device or network under consideration.

The transformations are obtained by the equations

$Z_1=Z_0 ({\frac{1+s_{11}}{1-s_{11}}})$

$Z_2=Z_0 ({\frac{1+s_{22}}{1-s_{22}}})$

Z1 and Z2 may be plotted for each of their corresponding s-parameter values.

The s-parameters for active devices are normally obtained directly by experiment.

One can of course theoretically derive a complete set of s-parameters for a passive network with a known circuit configuration and component values. The set independent variable would be operating frequency.