MATLAB Answers

Simulink S-Parameters Plotting

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Mark on 10 Aug 2013
I would would like to know how to plot the frequency response when two Simulink SimRF S-Parameters blocks are connected to each other. With a single block you can simply run the Plot function built within but now I have two blocks in series.

Answers (1)

Giorgia Zucchelli
Giorgia Zucchelli on 14 Aug 2013
Dear Mark,
If you are using components from the Equivalent Baseband library, you can plot the S-parameters of the overall cascade of components using the visualization pane of the Output Port.
If you are using components from the Circuit Envelope library you need to build a simulation testbench to verify the S-parameters of the network under test. In terms of best practices, I would recommend to:
  • Use "Time Domain Modeling" for the S-parameters. Verify that the rational fitting is sufficiently accurate.
  • Use a relatively small simulation sample time in the SimRF parameters block (e.g. 4 or 8 times smaller than the envelope simulation bandwidth)
  • Use a random number source to excite the chain with a wideband signal
  • Use a Spectrum Analyzer to visualize the frequency domain output signals (e.g. S21, S11). An alternative is to use the "Baseband Transfer Function" block from the free Mixed-Signal Library that you can download from here:
  • Use an ideal coupler to probe the reflections at the input / output. You can build an ideal coupler using an S-parameters block with these [0 1 0;1 0 0;0 1 0] parameters.
With this approach you will be able to verify the behaviour of the overall network of S-parameters as it is simulated in the time domain. If you just need to inspect the S-parameters in the frequency domain, you can just use RF Toolbox functions, or refer to the SimRF shipping demo "AC Analysis of an RF System".
With best regards, Giorgia

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