FTΩ\OmegaΩ is sampling frequencywhich means sampled FT also has impulse train like periodS(jω)=2πT∑∞δ(Ω−kΩs)S(j\omega) = \frac{2\pi}{T}\sum_\infty \delta(\Omega - k\Omega_s)S(jω)=T2π∑∞δ(Ω−kΩs)