Here's some math:

$$\phi_{n}(\kappa) = \frac{1}{4\pi^{2}\kappa^{2}}\int_{0}^{\infty}\frac{\sin(\kappa R)}{\kappa R}\frac{\partial}{\partial R}\left\lbrack R^{2}\frac{\partial D_{n}(R)}{\partial R} \right\rbrack\, dR$$