The radiofrequency behavior of passive circuit components: The inductor – Part 2

The RF behaviour of the inductor is complex. This is essentially due to two reasons. First the inductor is rarely realized through an empty coil. Indeed practical realizations usually employ ferromagnetic materials, such as ferrites, whose electrical properties are frequency dependent, may exhibit a non-linear behaviour and have non-negligible (frequency dependent) losses. Second the impedance of the inductor increases when frequency increases, thus it tends to unintentionally couple to the surrounding metallic structures, the maximum coupling being at resonance where the inductor impedance is maximum. The basic (intentional) behaviour of the inductor is here first introduced. Then the non-ideal (unintentional) behaviour at RF is described (namely spurious electric field coupling, losses, relaxation, temperature dependence and saturation). Examples of practical inductor realizations are offered.