Lowpass filters with almost-maximally flat passband and Chebyshev stopband attenuation

Abstract

A class of the almost-maximally flat (AMF) lowpass filters with Chebyshev stopband attenuation, referred to as AMF filters, is discussed. Allpole lowpass filters' transfer functions are first derived by using parameters α and β of modified Jacobi polynomials J (αβ) n (V) such that passband attenuation is minimised, and obtained transfer functions are then augmented by adding one or several pairs of jV-Axis transmission zeros. The magnitude characteristics of proposed filters are compared with those of the Chebyshev II filters and are found to be superior, both in the passband and in the stopband.