Greetings: There is so much good stuff on RF Cafe that there is no way to list or
link to all of it here. Please use the Search box or the Site
Map to find what you want - there is a good chance I have it. Thanks!
poles lie along a circle similar to the Butterworth filter, but are spaced approximately equal distances apart
relative to the real axis rather than at equal angular distances. Prototype value real and imaginary pole
locations (ω=1 at the 3dB cutoff point) for Bessel filters are presented in the table below.
diagram shows the location of poles for a 4th-order Bessel lowpass filter.