S-parameters peaks and bandwidth

Hey guys

I have a S-parameter touchstone file with such a characteristic:

I want to use findpeaks function for determination of the width and central frequency of each peak, but I get an error.

[Deepak Kumar]

What is the error you are getting ? can you share the data ?

You can refer the below documentation link to know more about "findpeaks" function

https://in.mathworks.com/help/signal/ref/findpeaks.html

[mikeeee]

Dear Deepak,

I have attached the data-file. The error that I get is:

Attempt to execute SCRIPT findpeaks as a function:

C:\Users\.....\findpeaks.m

Error in findpeaks_sparam (line 3)

peaks = findpeaks(S_ML,freq_sim)

Code is:

 S_ML = sparameters('file.s2p');           
 freq_sim = S_ML.Frequencies;
 peaks = findpeaks(S_ML,freq_sim
 

Answer 1

[Deepak Kumar]

Couple of points that I noticed in your code:

S_ML is S-parameter object

>> S_ML

S_ML = 

  sparameters: S-parameters object

       NumPorts: 2
    Frequencies: [10000×1 double]
     Parameters: [2×2×10000 double]
      Impedance: 50

  rfparam(obj,i,j) returns S-parameter Sij

The input data to “findpeaks” function must be a vector,real and of the type ‘single’ or ‘double’. So, you cannot give S_ML directly as input to the “findpeaks” functions as the S_ML is neither ‘single’ nor ‘double’.

Refer the below documentation for details:

https://in.mathworks.com/help/signal/ref/findpeaks.html

You can extract the parameter values like below

  >>x= S_ML. Parameters;

But I noticed that, x= S_ML. Parameters, is of the size and it has complex values. Since 'x' is not a vector rather 3-D data (It’s because it is representing all the S parameters for (S11,S12,S21,S22) for a two port network and 10000 is the number of frequency values at which the S-Parameters are calculated).

Please refer the below documentation for more details:

https://in.mathworks.com/help/rf/ug/s-parameter-notation.html

you can try to extract the individual S values, something like below

  >>k1=x(1,1,:)  %for S11

and, reshape it to make it a vector

  >> k1=reshape(k1,10000,1)

Then, take only the magnitude values,

  >>k1=abs(k1);

Now, you will be able to use “findpeaks” function.

Hope this helps!

Answer 2

[Deepak Kumar]

Can you try to rename your script file (findpeaks.m) and check if it resolves your issue ?

[mikeeee]

No, it does not