how to make fft2 surf plot with z axis in dB?

i tried to normalize this matrix with the maximum

and: p=10*log10(p);

but i get mess

how can i avoid that?

Answer 1

[Star Strider]

Without access to your data, it’s difficult to say. Two possibilities:

First:

p = 10*log10(abs(p));

Second:

p = 10*log10(abs(p)+1E-2);

[Star Strider]

Interesting, to say the least!

This is what I get with your data and this code:

D = matfile('Kobi_pmat.mat');
P = D.P;
LP = 10*log10(abs(P));

figure(1)
mesh(LP)
grid on
axis([600  800    600  800    -30  0])
xlabel('x')
ylabel('y')
zlabel('F(x,y) (dBi)')
title('Fourier Transform of Rectangular Reflector')

producing this plot:

Answer 2

[Youssef Khmou]

This problem does not occur with the following test :

H=exp(-randn(10).^2);
F=abs(fftshift(fft2(H,200,200)));
F=F/max(F(:));
surf(20*log10(F));
try abs() as mentioned earlier .

Answer 3

[Kobi]

here is my data file:

https://dl.dropboxusercontent.com/u/38094905/pmat.mat

you can load it like this:

 data=load('pmat.mat');

 P=data.P;