Design of generalised Chebyshev lowpass filters using coupled line/stub sections

Abstract

A new method for the design of distributed lowpass filters enables exact realisation of the series short circuited transmission lines which are normally approximated via unit elements in other filter realisations. The filters are based upon basic sections using a pair of coupled lines which are terminated at one end in open-circuited stubs. The approach enables realisation of transmission zeros at the quarter -wave frequency hence giving improved stopband performance. A complete design is presented and demonstrates excellent performance in good agreement with theory.