Several observations can be made from the above graph of second order bandpass filters of Bessel, Butterworth, Gaussian, and Chebychev shape. The group delay of the Bessel is flat in the passband; whereas the Gaussian group delay is “bullet” shaped. The group delays of the Butterworth and Chebychev have more variation and have a somewhat inverse shape in the Passband relative to the Gaussian. They also have peeks near their cutoff frequencies.

The amplitude response of the Chebychev is better than the Butterworth, which is better than the Bessel. Note that the graph does not depict this, because the 3 dB bandwidths are not equal. The Bessel and Gaussian filters are also more sensitive to load variations which may seriously affect the good group delay or phase shift response of these filters. In conclusion, the better the group delay response of the filter the worse the amplitude response.

Filtronetics, Inc. can custom design a filter using design techniques that optimized amplitude, return loss, group delay, phase linearity and ringing characteristics.

References
A. Zeverev, Handbook of Filter Synthesis, John Wiley, New York, 1967, p. 73