Attenuation filters
Transfer function of electrical filters

If we try to create a filter defined solely by a loss template, without considering its phase-shift behavior, we introduce a considerable simplification. In fact, we'll see that, in this case, we can find a transfer function with minimal phase shift (see the article Linear Electric Circuit Theory [E 3 000] for an explanation of this concept) that approximates the ideal solution as closely as we like. And we know how to calculate the simplest possible function for a given approximation.

Unfortunately, functions with minimal phase shift are governed by a relationship between amplitude and phase that makes it impossible to specify these two behaviors independently of each other [8]