A design method for low‐pass filter using nonuniform transmission lines

Abstract

AbstractThis paper presents a design method for the low‐pass filter using nonuniform transmission lines. First, two kinds of nonuniform transmission lines are considered‐parabolic and exponential lines. the strict and low‐frequency approximate solutions are determined for two kinds of nonuniform lines and the mixed lumped and distributed circuit consisting of parallel capacitors and uniform transmission lines. By equating those two kinds of solutions, an approximate expression is obtained for the nonuniform line made up of mixed lumped and distributed circuit. Then by using this approximate equivalence relation, sections of pre‐designed lumped and distributed circuits are approximately replaced by nonuniform lines. Due to the replacement by approximate elements, the resulting circuit has characteristics different from the original lumped and distributed circuit. It was seen from several numerical examples that the circuit made up of nonuniform lines has steeper roll‐off characteristics and larger attenuation in the stop‐band than the lumped and distributed circuit and are suited for a low‐pass filter. It is observed also that the circuit made up of nonuniform lines can reduce the number of lumped capacitors more than the lumped and distributed circuit.