An approximation algorithm for irregular-ripple filters

Abstract

A simple formulation is presented for the approximation of low-pass filters with specified number and level of ripples in the passband and stopband. The order of any finite attenuation or transmission zero can be specified as simple or double, and these zeros are not restricted to the jw axis. The method can be used to numerically obtain the characteristic functions of approximations ranging from the Butterworth to the elliptic ones.<>