In this paper we present an enhancement to our previously reported approximate modal interface-solution space projection (AMI-SSP) method [1], which is a combined domain decompostion-model order reduction method for efficient broadband full-wave analysis of multilayer printed circuits. With the AMI method, a multilayer circuit board can be analyzed layer by layer, which leads to a significant improvement in the computational efficiency. The method has been further combined with a multipoint model order reduction method, SSP [2], to achieve a fast frequency sweep. The AMI-SSP has been implemented with the finite-element method, which is well known for its excellent capability of analyzing complicated structures with arbitrary geometries and materials. The formulation in [1] assumed consistent meshes at an interface (via-holes, for example) between adjacent layers, and as a result posed a restriction on the mesh generation. There is no such a restriction in the enhanced method presented in this paper, and thus the mesh in each layer can be truly generated independently. Furthermore, depending on the geometry and complexity of interconnections, different types of elements or even different orders of basis functions can be applied in different layers as long as the same number of modes is used in the modal expansion at each interface. Some important properties of the enhanced AMI-SSP can be summarized as follows: 1) The AMI-SSP only yields the fields at via-holes and ports since volume fields are not necessary in the calculation of S-parameters. 2) The mesh in each layer can be generated independently without the need of consistent meshes on the two sides of an interface. 3) An independent interface system is generated for each layer, and therefore, when the circuit configuration in a certain layer changes, only that layer needs to be re-simulated. This makes the optimization of a circuit much more efficient.
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