How To calculate Q Factor and Resonance Frequency of S Parameters

Hey There!

I'm dealing with some .s2p files for my Degree Thesis but unfortunetely I don't know how to calculate Q Factor and Resonance Frequency of that file by using Matlab.

Can you help me, please?

Thanks In Advance

[Mathieu NOE]

hello

do you have a code and a s2p file to play with ?

[FRANCESCO MARINO]

Yes, I have a .s2p file. Why? Do you want me to send it to you?

Answer 1

[Yukthi S]

Hi Francesco

I understand that you wanted to calculate Q factor and Resonance frequency from a .s2p file using MATLAB.

The following steps can help you. Also make sure that your system has RF toolbox installed, otherwise MATLAB will throw an error.

• Read the .S2P file into MATLAB. You can use “sparameters” function to do so. Please refer to this existing MATLAB answer to get more insights: https://www.mathworks.com/matlabcentral/answers/432374-how-do-i-export-data-from-an-s2p-file-in-matlab
• Calculate the Frequency and S21 parameter.
• Find the resonance frequency.
• Calculate the bandwidth.
• Calculate the Q-factor

The following code can help you to get an idea:

% Load the .s2p file using the sparameters function
s2pObject = sparameters('your_file_name.s2p');
 
% Extract frequency and S21 parameter
frequency = s2pObject.Frequencies;
S21 = s2pObject.Parameters(:,2,1); % S21 parameter

% Find the magnitude of S21
S21_magnitude = abs(S21);
 
% Find the index of the maximum magnitude of S21
[peak_magnitude, maxIdx] = max(S21_magnitude);
 
% Resonance frequency is the frequency at this index
resonance_frequency = frequency(maxIdx);
 
% Convert peak magnitude to dB
peak_magnitude_dB = 20 * log10(peak_magnitude);
 
% Find the frequencies where the magnitude drops 3 dB from the peak
three_dB_down = peak_magnitude_dB - 3;
idx_bandwidth = find(20 * log10(S21_magnitude) >= three_dB_down)
 
% Bandwidth is the difference between the upper and lower frequency limits
bandwidth = frequency(max(idx_bandwidth)) - frequency(min(idx_bandwidth));
 
% Calculate the Q factor
Q_factor = resonance_frequency / bandwidth;
 
% Display the results
fprintf('Resonance Frequency: %f Hz\n', resonance_frequency);
fprintf('Q Factor: %f\n', Q_factor);

Hope this helps.