In analog filter technology, there are several basic types that are characterized by certain transmission properties and are used accordingly. These include the Bessel filter, named after the German mathematician Friedrich Bessel (1784-1846), the Butterworth filter and the Chebyshev filter.
The Bessel filter is characterized by a constant group delay and a linear phase behavior in the passband( DB) of the filter.
The linear phase response results in a constant time delay of all frequencies transmitted in the passband. This property is particularly interesting for distortion-free transmission of broadband signals such as step signals, square-wave signals or pulses transmitted without overshoot and ringing. However, the slope is flatter than the other two types of filters mentioned.
To achieve a high stopband attenuation, Bessel filters require a higher filter order than other filters.