Bessel RF Filter Basics

- basics of the Bessel Filter - its performance, key facts and how it can be used in RF and other filter applications.

Bessel filter tutorial includes:

    •  Bessel filter basics

The Bessel filter is a linear form of filter that provides a maximally flat group delay or propagation delay across the frequency spectrum, but offers a slower transition from pass-band to stop-band than for other forms of filter of the same order.

However, the Bessel filter is not used as widely as the Butterworth of Chebyshev filters for RF applications, although the fact that it has a maximally flat group delay means that Bessel filters are often used in audio applications such as audio cross-over networks.

Bessel filter development

The Bessel filter takes its name from a German mathematician and astronomer named Friedrich Bessel who lived between1784 and 1846. Bessel developed the mathematical theory on which this form of filter is based.

Occasionally the filters may also be referred to as Bessel-Thomson filters. This is because W. E. Thomson developed the methodology of using Bessel functions within the design of this form of filter.

Bessel filter basics

Some of the key features of the Bessel filter can be summarised as below:

• Maximally flat group delay:   The maximally flat group delay of the Bessel filter means that it equally exhibits a maximally linear phase response.
• Overshoot:   A direct result of the maximally flat group delay of the Bessel filter it gives an output for a square wave input with no overshoot because all the frequencies are delayed by the same amount.
• Slow cut-off:   The transition from the pass band to the stop band for the Bessel filter is much slower or shallower than for other filters.

By Ian Poole