Maximally flat low-pass filters with steeper slopes at cutoff

Maximally flat rational functions with one pair of imaginary axis zeros are compared with the all pole Butterworth function for low-pass filter applications. It is shown that by using the location of the zeros as a parameter an advantageous trade between attenuation in the stopband and sharpness of the cutoff characteristic can be made. Graphs which serve as guides in the placement of these zeros and a practical design example are included.