In some publication I have found a formula that for some reason squares signal in time domain. I am analyzing it now.
What should be the Fourier transform of a signal that was squared in time domain? I do not understand why $\mathcal{F}[sin(x)^2]$ results in peak in zero and why side peaks are moved.
I fully understand the fact that multiplication in time domain is convolution in frequency domain and squaring is just $x\times x$.