And what's the best bypass cap? Well, a single, plain, cheap aluminium electrolytic!
Attached is the impedance plot for a 47?F, 25V electrolytic cap, measured with lead lengths compatible with mounting it snugly on a PCB. Their narrow pin spacing helps a lot in keeping their ESL low. I kept the same scale to make comparison easy.
YES, a single 47?F electrolytic is a much better bypass cap than a parallel combination of two ceramic caps of different values! Even in the low VHF range!
The problems with electrolytic caps is that their ESR rises with age, and rises much faster if they run hot, or if they have to carry large ripple current. So they can't be applied in every situation. But in situations that are kind to them, they are the cheapest and easiest way to get an excellent wideband bypass.
