Why the Gaussian after chirp z-transform (CZT) is not correct?
3 Ansichten (letzte 30 Tage)
Ältere Kommentare anzeigen
Dear all,
I would like to use the CZT to amplify the certain frequency range. When I use a real Gaussian signal as a test, the result of CZT transformation doesn't make sense (Gaussian should remain as Gaussian after czt). In my mind, the fft requires the zero frequency at the [1,1], so I use ifftshift(signal) and the result after czt are weird with multiple copy of original signals.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/389883/image.jpeg)
clear all;
close all;
Lx=1;
Ly=0.8;
M=200;
N=160;
dx=Lx/M;
dy=Ly/N;
x=linspace(-Lx/2,Lx/2,M+1);
y=linspace(-Ly/2,Ly/2,N+1);
% corresponding to M+1 size
fx=-1/(2*dx):1/Lx:1/(2*dx);
fy=-1/(2*dy):1/Ly:1/(2*dy);
% generate Gaussian signal
[Y,X]=meshgrid(y,x);
w0=0.05;
amp=exp(-pi*(X.^2+Y.^2)/w0^2);
figure;
imagesc(amp);
% targeted frequency
sampx=1/dx;
sampy=1/dy;
fx1=-18;
fx2=18;
fy1=-18.5;
fy2=18.5;
wx = exp(-1i*2*pi*(fx2-fx1)/(M*sampx));
ax = exp(1i*2*pi*(fx1)/sampx);
wy = exp(-1i*2*pi*(fy2-fy1)/(N*sampy));
ay = exp(1i*2*pi*(fy1)/sampy);
% czt
tmp2=czt(amp,M,wx,ax);
% tmp2=czt(ifftshift(amp,2),M,wx,ax);
amp_f2=czt(tmp2.',N,wy,ay);
figure;
subplot(1,3,1);
imagesc(fx,fy,abs(amp_f2));
colormap('jet');
subplot(1,3,2);
imagesc(fx,fy,real(amp_f2));
colormap('jet');
subplot(1,3,3);
imagesc(fx,fy,imag(amp_f2));
colormap('jet');
0 Kommentare
Antworten (0)
Siehe auch
Kategorien
Mehr zu Spectral Measurements finden Sie in Help Center und File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!