why are sinewaves used for phase analysis?

[konzen]

guys, recently my lecturer asked the class this question. he asked why are sinewaves chosen over square waves for phase analysis and he says the answer has got something to do with harmonics? anyone can shed light on this question?

i've tried googling but without any luck.

thanks a bunch

 

[stevez]

Hint - Fourier

 

[konzen]

okay, thanks alot