# phase angle of harmonic

I have generated sinsuoids containing fundamental with harmonics using C++. Fundamental frequency is 50 Hz and each of the harmonic has phase offset of 60 degrees. I have applied flattop window before performing and N point FFT. Magnitude repose is correct. Phase reponse is wrong. I should expect 60 degree in all 100,150,200,250 Hz. I have attached the results.

Sampling rate : 40000 Timeduration : 1s Maximim amplitude of each of the harmonic : 1

Any help would be highly appreciated.

Regards, Faisal

Your window is centered around the middle of the time window. This corresponds (roughly speaking) to a delay of half the window size and corresponding additional phase of $e^{-j \cdot \omega \cdot t}$