Bessel filters have the following characteristics:
You can use Bessel filters to reduce nonlinear-phase distortion inherent in all IIR filters. High-order IIR filters and IIR filters with a steep roll-off have a pronounced nonlinear-phase distortion, especially in the transition regions of the filters. You also can obtain linear-phase response with FIR filters.
The following figure shows the magnitude and phase responses of a lowpass Bessel filter.
In the previous figure, the magnitude is smooth and monotonically decreasing at all frequencies.
The following figure shows the phase response of a lowpass Bessel filter.
The previous figure shows the nearly linear phase in the passband. Also, the phase monotonically decreases at all frequencies.
Like Butterworth filters, Bessel filters require high-order filters to minimize peak error, which accounts for their limited use.