Search

The eigenmode transformation technique is formulated for the analysis of inhomogeneously filled shielded waveguides containing metal inserts. The permittivity of the filling medium may be an arbitrary function of the transverse coordinates. The method is based on expanding the electromagnetic field in terms of the eigenmodes of the corresponding empty shielding waveguide. The metal inserts have first the effect of linearly transforming the eigenmodes of the empty guide into those of the shielded waveguide containing the metal inserts (including the TEM-modes). Next the inhomogeneity of the filling medium is taken into account which leads to a proper matrix eigenvalue problem. In addition an alternative formulation is derived from a variational approach. Results of both formulations are compared for a shielded circular dielectric waveguide. The eigenmode transformation technique is applied to various types of planar transmission lines, i.e., coupled microstrip lines, finlines, and coplanar lines. The results are compared with those of other methods.

For the modal analysis of complex gyrotron cavities, complete sets of eigenfunctions of the corresponding completely shielded cavity are required. In this contribution, it is shown that the generalized scattering matrix method which is well-known for the computation of the resonance modes can also be applied to the calculation of the irrotational electric and magnetic eigenfunctions. The irrotational eigenfunctions are computed for some circularly symmetrical structures. The validity of the method is checked by investigating a spherical cavity for which the analytical solution is known. Furthermore, a special subdivision of tapered cavity sections is presented which considerably improves the numerical efficiency of the method. For a standard gyrotron cavity, the field in the source region is computed with and without making use of irrotational electric eigenfunctions. It is demonstrated that the accuracy and the numerical efficiency of the modal expansion of the cavity field in the source region is improved if these eigenfunctions are included in the analysis.

A method for the computation of irrotational magnetic eigenfunctions in complex cavities is presented. It is shown that the 'TE[subscript 00] waveguide mode' has to be included in the analysis. For a simple cavity, it is analytically demonstrated that the irrotational magnetic eigenfunctions have to be taken into account in field expansion methods. Numerical results are given for some structures. The validity of the method is checked for a spherical cavity. Furthermore, it is shown how the numerical efficiency of the method can considerably he improved by a special subdivision of tapered sections.

The generalized spectral domain (GSD) technique is applied to the analysis of waveguide coupling by axially uniform slots. For a slotted-circular waveguide, cut off wavenumbers of TE and TM modes as well as the corresponding field distributions in the composite waveguide are determined and compared to that obtained by other methods. Plots of the field lines corresponding to the dominant as well as a number of higher order modes are presented. It is shown that considering the [H.sub.00] modes in the comprising waveguides is necessary. Furthermore it is demonstrated how the efficiency of the method regarding accuracy and CPU time requirements can considerably be enhanced if infinite sums over eigenmodes which have to be evaluated are replaced by closed-form expressions.

A method based on the volume integral equation (VIE) formulation is presented which can be used to analyze inhomogeneously filled cavities of arbitrary shape to which cylindrical waveguides of arbitrary cross section are coupled. The inhomogeneity inside the cavity is described by a spatially dependent permittivity. The method is applied to the problem of scattering by dielectric bodies inside waveguides. Furthermore, it will be demonstrated how the convergence of the method can be accelerated.