To compute magnitude and phase spectrum

Hello,

I have a function, for that I need to find the magnitude and phase spectrum on matlab. Can someone please help me with the code, please?

The parameters are A=2 a=4 -20<=F<=20.

This is the function.

[Shubham Gupta]

Where is 'F' being used in the function? Also, what do you mean by 'magnitude of the function'?

[Sri Srujan Gollapudi]

Even I'm not sure of that. But if we leave out the limits of F, how can I find the magnitude and phase sepctra with given values of A and a for the above fucntion?

Answer 1

[Deepak Kumar]

I'm not sure what F is referring here.

However, we can find the Magnitude and Phase spectrum of a function using FFT function in matlab. I have wrirren the below code to evalute the magnitude and phase spectrum of the given function and also plotted them.

clc
clear
close all
A=2;
a=4;
fs=1000; % Sampling frequency
t=0:1/fs:1; %Time 
x=A*exp(-a.*t); %Signal
plot(t,x) %Plotting the time domain signal
xlabel('t');
ylabel('x(t)');
title('Time domain Signal')

N=length(x);
N1=2^nextpow2(N);
X=fft(x,N1);
X=X(1:N1/2);%Discard Half of Points
X_mag=abs(X); %Magnitude Spectrum
X_phase=phase(X); %Phase Spectrum
f=fs*(0:N1/2-1)/N1; %Frequency axis
figure
plot(f,(X_mag/N1)); %Plotting the Magnitude Spectrum after Normalization
xlabel('Frequency (Hz)');
ylabel('Magnitude Spectrum');
title('Magnitude Spectrum vs f')

figure
plot(f,X_phase); %Plotting the frequency domain
xlabel('Frequency (Hz)');
ylabel('Phase Spectrum');
title('Phase Spectrum vs f')

Please refer the below documentation for more details about the FFT function:

https://www.mathworks.com/help/matlab/ref/fft.html

[WJ]

Hello can you please help me, i am trying to do this for a half wave rectified signal, i am new to matlab and i am trying to study it, please help me

[Gerard MacDermott]

Hi,

In the line 'X_phase=phase(X); %Phase Spectrum'

what is the 'phase' function? Is this a personal functions? My MATLAB doesn't recognise it? I am using MATLAB 2020.

Cheers,

Gerry

[Betuel Bulande]

Hi, just replace phase(X) for angle(X).

[Gowtham K]

thanks

[Juan Palomo]

hi, if this spectrum is the single side spectrum (comment on code:

X=X(1:N1/2);%Discard Half of Points

) should'nt the amplitude be multiplied by 2 like in https://es.mathworks.com/help/matlab/ref/fft.html?lang=en "Compute the two-sided spectrum P2. Then compute the single-sided spectrum P1 based on P2 and the even-valued signal length L.

P2 = abs(Y/L);
P1 = P2(1:L/2+1);
P1(2:end-1) = 2*P1(2:end-1);

"