In the future High Energy Physics will need very long linear colliders for e+e‐collisions in the TeV range to verify the laws of elementary particles with sufficiently high luminosity. Most designs currently under discussion use multibunch operation. Therefore the study of higher order modes excited by previous bunches in the train becomes even more important for the optimal design of the accelerator components. Usually the electromagnetic properties of these components are calculated by computer codes that discretize Maxwell’s equations. For long tapered disc‐loaded waveguides however, these methods would need the solution of extremely large algebraic eigenvalue problems with many clustered eigenvalues. This is numerically difficult. In this paper the electromagnetic waves in tapered circular multi‐cell structures are calculated by a modal field matching method. The structure is subdivided into subregions of constant circular cross section. In each subregion the electromagnetic fields are expanded in orthogonal series over discrete modes. The field solutions are obtained by field matching at the transverse interfaces between the subregions. The scattering matrix formulation is used to calculate the amplitudes of the field expansion. This formulation assures numerical stability. Numerical results are obtained by appropriate restriction to a finite number of modes. Some convergence investigations are presented as well as comparisons with a grid‐oriented numerical method and an equivalent circuit model. The field distribution of deflecting dipole‐modes is analyzed for a 180‐cell tapered disc‐loaded S‐band‐structure.

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