Why Bessel?

Hello all,

I recently was going over an old electronic design, and I noticed that
the designer used a 4rth order Bessel low pass filter where low pass
filtering was needed. (I know it was a Bessel filter because it so
marked ;) ). The bessel filter was realized with 2 op-amps and many
resistors and a few capacitors. Knowing the designer (designer is
overseas now for a few years...) was always making his designs as
compact as possible, - (had to twist both of to his arms to make him
insert failsafe redundancies :) ) - why would he use such a bulky
method for low pass filtering?
The bessel low pass filter cuttoff frequency is ~100Hz. It's sharpness
would have to be, hmmm, well pretty sharp. After all it was initially
intended for a medical application. I would hazard a guess that is what
warrants the 4rth order. But why a Bessel topology? I know bessel
filters are usefull in audio applications because of the linear phase
property they have, but this is not an audio application.
Basically, I am asking why Bessel ? Does Bessel have anything special
that I am anaware of?

-Roger

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