Several designs for linear colliders for electron-positron-collisions in the TeV range are currently under discussion. Most of them will use long trains of bunches. Therefore the study of higher order modes excited by previous bunches in a train became even more important for the optimal design of the accelerator components. Many of the designs use long tapered disc-loaded waveguides for acceleration. Numerical reasons hinder the mode analysis of these long structures by discretization methods. In this paper the electromagnetic waves in tapered multi-cell structures with circular cross section are calculated by a modal field matching method in which the scattering matrix formulation is used to calculate the amplitudes of the field expansion. Some remarks on convergence aspects are made. The field distribution of deflecting dipole modes is analyzed for a 180-cell tapered disc-loaded S-Band structure as well as for a 36-cell test structure. For the 36-cell test structure comparisons with a grid-oriented numerical method, an equivalent circuit model and measurements are also presented.

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