FFT (Fast Fourier Transform) - a method for phase continuation

[petol]

Hello everyone,
Finding a good query to find an answer in www search engines isn't as easy as I thought. The subject is very narrow and sophisticated.
When one performs a FFT, he/she/IT ;) gets the amplitude and phase spectra. The phase spectrum ranges from -PI to PI. Then, there are of course places where the phase spectrum is discontinuous because it exceeds the range. How to obtain such continuous phase spectrum? Does anyone know the idea for this?
Kind Regards

 

[petol]

Maybe this picture will help. I duplicated the same phase spectrum several times and shifted n*PI each.
I'm looking for such method because I've seen it in some paper works.