I guess it is a hardware isue, because the bands are repeated uniformly and I guess also that the bands are going around completely.
What I can't guess whats the matter: bands or neckings. Beginning to print the rounded top layers the width is perhaps normal ???
The slicing software S3D doesn't contain any setting what can cause that, exepted the model is drawn in this way or the STL-file has issues.
The filament normally has a very consistent diameter (variations +/- 0,05 mm) so it is possible that in the region of a band the filament brings out really much more material (or in case of neckings, it is poor) - not very plausible- . Also the extruder motor may have an issue . And at last it may be that the print temperature is raising up and down.