Mutual impedance spectrum for a quadrupolar configuration, according to the geometry presented in the figure, and compatible with the one of the RPC-MIP instrument on board the Rosetta spacecraft. Here, the ratio of plasma to electron cyclotron frequency is f_pe/f_ce = 1.4. The effect of electron-neutral scattering, modeled by Eq. (4), is presented by the decreasing electron-neutral collision frequency on the horizontal axis, from left to right.