RF Toolbox: Plotting S-parameters

Question

ArSAT 2023-4-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1939624-rf-toolbox-plotting-s-parameters

回答： Abhishek 2023-4-11

Hi,

I recently purchased the RF toolbox addon for MATLAB. I have been using the matching network designer and so far have encountered a strange issue.

The issue is that the S-parameter plots in the matching network designer app are not the same as those generated by manual code, i.e: matchingnetwork(), sparameters() and rfplot().

For example given the following code snippet (for an L match):

f       = 1.5e9;       
Zin     = 50;     
Zl      = 25;     
n = matchingnetwork('CenterFrequency',f,'Bandwidth',7.5e8,'LoadImpedance',Zl,'SourceImpedance',Zin, 'Components',2);
freq = linspace(n.CenterFrequency-n.Bandwidth/2,n.CenterFrequency+n.Bandwidth/2);
S = sparameters(n,freq,50,1)
rfplot(S,1,1)

The following plot is obtained:

Which is completely different to the S1,1 obtained by constructing the same circuit (L-match) in the matching network designer:

Why am I not seeing a minimum point in the first image/plot? I expected the two plots to be the same. Am I plotting S1,1 incorrectly?

Thank you in advance.

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Answer 1

Abhishek 2023-4-11

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https://ww2.mathworks.cn/matlabcentral/answers/1939624-rf-toolbox-plotting-s-parameters#answer_1213554

在 MATLAB Online 中打开

Hi Arsat,

I understand that you're trying to figure out difference between plot of S parameters using the matchingnetwork function and through app.

Notice that when using the following command for calculating the S parameters, the load impedance information is not being transferred to the sparameter function.

s = sparameters(n,freq,RefZ0,ckt_no)

Consequently, the default value is utilized, and any user-defined values specified during the design of the matching network is ignored. Refer to: Calculate S-parameters for RF data, network, circuit, and matching network objects - MATLAB sparameters (mathworks.com)

As a result, it is recommended to utilize the following command directly without defining the s-parameters:

rfplot(n,freq,1)

This will give you the following result which matches with one produced by Matching Network Designer app.