A new approach to the network modelling of capacitive irises and steps in waveguide

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Abstract
Classical network representations of waveguide discontinuities assume monomode operation and involve elements which depend not only upon geometry, but also on frequency.Later approaches to the problem consist of numerical techniques. These are unsuitable for synthesis since they do not yield equivalent networks and involve repeating the field analysis at each frequency, which is cumbersome for applications to wideband design.A recent approach permits to derive wideband equivalent networks with elements which depend only upon geometry. In this contribution capacitive irises, steps and combinations are treated. These discontinuities occur in filters, transformers, etc. where higher‐order mode interaction cannot be neglected for closely spaced discontinuities. Whatever this spacing may be, higher order mode interaction always occurs in oversize guide. Higher order mode interaction fits naturally into the network modelling presented here. The resulting network representations are either in canonical Foster form of the first type or easily reducible to it. This approach is based on a Rayleigh–Ritz variational solution of the field problem and involves manipulations with small matrices only.The accuracy of the method is demonstrated for a number of basic configurations, while its flexibility is illustrated by providing simpler equivalent networks, applicable when extreme accuracy is not required. The elements involved are given in graphical or in simple analytical form.

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