Though I thoroughly understand the complex index signal, but there is always such a wonder: for a signal, it contains the frequency component of omega, omega, 2 5 omega, omega of & gt; 0, then the signal bandwidth is 4 omega, should not be 8 ohms, right? For example, f (t)=1 + Σ sin omega t (k), k=1, 2, 3,... Ten, omega & gt; 0, then the signal bandwidth should be 10 omega, rather than 20 omega, right? Of f (t), however, Fourier transform is bilateral spectrum, why?