% Simulation parameters fsampling = 20e6 ; % sampling frequency Tsampling = 1/fsampling ; % sampling period N = 512 ; % DFT size % Pulse parameters A = 1/1e-6 ; % pulse amplitude D = 1e-6 ; % pulse duration t = (0:Tsampling:(N-1)*Tsampling) ; pulse = A*rectpuls(t-D/2,D) ; f = (fsampling/N * (0:N-1)) ; % simulated spectrum simulated_spectrum = 1/fsampling*fft(pulse,N) ; % exact spectrum exact_spectrum = A*D*sinc((0:fsampling/1000:fsampling/2)*D).*exp(- j*pi*(0:fsampling/1000:fsampling/2)*D) ; figure plot(f(1:N/2)/1e6,20*log10(abs(simulated_spectrum(1:N/2))),'k') hold on plot((0:fsampling/1000:fsampling/2)/1e6,20*log10(abs(exact_spectrum)),'r') hold off axis([0 5 -70 10]) xlabel('frequency (MHz)') ylabel('magnitude (dB)') legend('simulation','analysis')