use RF toolbox to plot S21 vs frequency for different dB signals

I have 30 s-parameter data sets but instead of just plotting s21 together on the same plot, I'd like to plot the value vs dB. I guess I need to find the s21 value at a number of equally spaced frequency values and then plot this. Does anyone have any ideas on how to implement this?

Answer 1

[Abhimenyu]

Hi Em,

From the information shared, I could infer that you want to plot "S21 parameter" values in dB versus frequency in MATLAB. Please follow the below mentioned steps to plot "S21 values" in dB for 30 S-parameter datasets at equally spaced frequency values:

• Extract the "S21 values" at the desired frequencies from each dataset. I am assuming that "S-parameter" data is stored in a format that MATLAB can easily read (e.g., .s2p files, .csv, or .mat files). Please load this data into MATLAB. If the data is in touchstone format (.s2p), MATLAB's RF Toolbox provides functions to read these files directly as given by this MATLAB R2024a documentation link: Basic Operations with RF Objects - MATLAB & Simulink - MathWorks India

clc
clear
% Example data: Replace this with loading your actual data
frequency = [1, 2, 3]; % Frequency points for dataset 1
s21_values = [0.5, 0.6, 0.7]; % S21 values for dataset 1 in linear scale

% Assuming 'frequency' is your vector of frequency values and 's21_values' is a vector of S21 values
% Repeat the process for each of your 30 datasets

• Convert the "S21 values" to dB using the formula: S21dB=20⋅log10(abs(S21))

% Convert S21 values to dB
s21_dB = 20 * log10(abs(s21_values));

• Create a frequency vector with equally spaced values across the range of interest.

% Create a vector of equally spaced frequency values
frequency_interp = linspace(frequency(1), frequency(end), 100);

• Interpolate the "S21 values" for these frequencies from your datasets using the "interp1" MATLAB function.

% Interpolate the S21 values in dB
s21_dB_interp = interp1(frequency, s21_dB, frequency_interp, 'linear');

• Plot the interpolated dB values against the frequency vector.

% Plotting
figure;
plot(frequency_interp, s21_dB_interp);
xlabel('Frequency (Hz)');
ylabel('S21 (dB)');
title('S21 vs Frequency');
grid on;

The above code will generate a plot for one dataset; you can loop over all your datasets to create multiple plots or overlay them on a single plot as needed.

To know more about "interp1" function follow this MATLAB R2024a documentation link: https://www.mathworks.com/help/matlab/ref/interp1.html

I hope this helps!