Plot Group Delay using Matlab with S-prameters

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sayyedjamal

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Hi there
Recently I tested a circuit and I just get S-parameters [in Mag (dB) and Phase (Deg.)]...now I want to plot Group Delay, and I don't know how to use Matlab's code to do that...

Could anybody help me?

Thx
 

If you want to do this numerically, then you could approximate the derivative using finite differences. As a simple example, let's assume Phi = sin(w). Then, the matlab code would be something like this:

Code: 
close all; clear all; clc;

% Define some values for w
w = (0:999)*0.01;

% Define Phi
Phi = sin(w);

% Compute differences
dPhi = diff(Phi);
dw = diff(w);

% Approximate -dPhi/dw
result = -dPhi./dw;

% Plot Phi and -dPhi/dw
plot(w, Phi);
hold on;
plot(w(1:end-1) ,result, 'r');
legend('Phi', '-dPhi/dw');

I think it would be far better to differentiate Phi analytically, but I guess this may not be possible.
 
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