High Frequency Behavior of Ferrites

I previously thought that the ferrite beads became lossy at high frequencies and that loss stays constant as f goes up. RB said a ferrite bead model is a parallel RLC circuit. At low frequencies, it is mostly inductive with resistive loss, then the inductive component decreases and the losses dominant. At sufficiently high frequency the parasitic capacitance between the ends of the bead begin to take effect and short out the lossy path.

Now I understand why the ferrite-loaded transmission line balun uses a string of beads with different permeabilities (mu). The high mu stuff works great at low frequency, but its lossy path begins to short out also at lower frequency. Hence, the balun needs low mu stuff which is still an effective loss element at higher frequencies.

hot end ======================== cold end
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low mu high mu