If the polymers of interest are ideal gaussian chains (or freely-jointed chains), in the limit of very long chains (allows performing a sort of "continuum transition"), the calculation of the structure can be carried out explicitly and result in a sort of Debye function:
With  being the polymer's radius of gyration.
in many practical scenarios, the above formula is approximated by the (much more convenient) Lorentzian:
which has a relative error of no more than 15% compared to the exact expression.