Analysis of inertance due to the higher order mode effects in a sudden area discontinuity

Abstract

It is well known that an area discontinuity generates evanescent higher order modes even at low frequencies within the plane wave limit. The effect of these non-planar modes can be accounted for by their inertance effect in the form of a discontinuity inductance expressed as a function of the Karal correction factor. Earlier investigators have provided approximate expressions for this factor based on the analysis of coaxial discontinuities. In this paper, a 3-D finite element analysis is used to verify the results of earlier researchers for the coaxial discontinuities and to develop a simple, accurate and comprehensive expression for the Karal correction factor as a function of radius ratio, frequency and the offset distance for a generalized discontinuity.