Eigenmode calculations are normally carried out by direct eigenmode solvers as in MAFIA's E-module[1]. These solvers need an enormous amount of computer resources, especially memory and computation time, if eigenmodes of long and complex structures with relatively small details have to be calculated. There are natural restrictions in constructing the mesh impact on the accuracy of the solutions. Especially the local and global mesh ratio is limited. This will produce additional mesh points in sections of the geometry which probably would not really need such a mesh refinement. A further resource consuming problem is given by the fact that the modeled volume has to be a cubus with a lot of unneeded material and mesh points. Finally most direct eigenmode solvers need to calculate the eigenmodes beginning with the smallest eigenfrequency. These modes need to be stored even if they are of less interest.

This paper will present a technique based on scattering parameters (S-parameters) that allows to split the complete geometry into subsections which can be modeled individually. This partitioning can be chosen in a way that geometrical properties like symmetry or repetitions of certain sections or groups of sections can be exploited. The S-parameter computations of each subsection are significantly smaller problems and can be performed on different machines. Then, the eigenfrequencies of the complete structure are determined by the combination of the scattering-parameters. Then the corresponding field distributions are computed by time domain or frequency domain solvers exciting waves of the appropriate frequency and amplitude at each port of each subsection and monitoring the field in the steady state case. This S-parameter approach gives the additional advantage of specifying a certain frequency range for the
search of the eigenmodes which will further reduce the computational effort.

* Work is supported by DESY

[1] MAFIA V4.0,CST GmbH,Büdinger Straße 2a,D-64289 Darmstadt,Germany