Why are the ripples on the chirpZ (CZT)? And for what or what means the lowpoints in the CZT?

Hello,

I have a question because I can not find any answers in the www. for my question! I have calculated with matlab the fft and the czt of a phase! Than I normalized the fft/czt and plotted them on a figure. In the figure I scaled the fft/czt with a length! The fft is in the upper window and the czt in the lower one! The czt is calculated and normalized in the same way as the fft. Only one is different in the CZT, the resolution from the czt is different because I have given more points (m)!

My question is yet!

Why are ripples/waves in the spectrum of the czt? And the lowpoints are the same points as the points of the fft?

For other sources (books, atricles, ...) I very glad!

Thanks for your help!