Hi Abid,
You are right in saying that one has to use the filter as per one’s requirements and specifications. Next you talked about the bessel’s functions….. Bessels function is just a mathematical trignometric function. It is used for solving the equations that contain trignometric functions with in a function…It is frequently used in electronics and signal processing .
It is a type of analog linear filter with a maximally flat group/phase delay (maximally linear phase response), which preserves the wave shape of filtered signals in the passband. Bessel filters are often used in audio crossover systems.
In all these applications if the mathematical equation generated have trignometic functions as a function of trignometric function then Bessels function can be used in solving them.
Hope you query has been answered.
Regards.