How can I smooth out my spectral phase plot in Matlab?

[snatcos]

Hi everyone,

I have this Matlab code :

function PH = testing
close all;
x = [0:1e-3:10-1e-3];
ph = -(x-5).^2;
y = exp(-(x-5).^2./(0.2^2)).*exp(i*2*pi*ph);

Y = fft(y);
Y = fftshift(Y);
PH = angle(Y);
X = (x(2) - x(1))^-1*linspace(0,1,length(x));

figure
plot(x,ph);
figure
plot(X,PH);
end

I build a gaussian curve with quadratic phase and Fourier Transform it. I expect to have a quadratic phase (with opposite sign) in the spectral domain, but I cannot have it correctly. The plot of PH shows jumps between adjacent points. Even using unwrap.m I cannot plot it well.

Thanks in advance for any help

 

[Adrmay]

.</code>It seems like the problem is caused by the finite length of the time domain signal. To solve this issue, you can try zero-padding your signal before taking the FFT. This will increase the frequency resolution and should help to reduce the jumps in the phase plot. For example, you can add zeros to the end of your x array with the following command:x = [x, zeros(1,length(x))];Then take the FFT of the new array. This should produce a smoother phase plot.Hope this helps!