Calculation of unbounded field problems in free space by a 3D FEM/BEM-hybrid approach

In recent times electromagnetic scattering calculations are often done by local methods such as Finite Elements or Finite Differences with approximate local absorbing boundary conditions because of their computational efficiency The exact formulation of the field problem by combining a local with a global method (boundary integral) has the drawback that fully populated matrices have to be handled, making the method of ten computationally intensive. But there are many cases in which such hybrid-techniques have advantages as compared with pure local methods. We present an FEM/BEM-hybrid approach and show its application to scattering problems with several separated finite inhomogeneous regions and to combined scattering/radiation problems. The calculation of radiation problems (e. g. antennas nearby inhomogeneous bodies) is especially attractive because radiation structures can be modeled by well-established integral equation techniques. Particular attention is paid to the evaluation of the coupling integrals for the BEM with singular integral kernels. The matrix solution procedure is optimized by a new renumbering technique for the FE-mesh. Numerical results are presented.