Solution of large multiscale EMC problems with method of moments accelerated via low-frequency MLFMA

The paper demonstrates that for large-scale electromagnetic compatibility problems not exceeding 120λ in size the low-frequency-multilevel-fast-multipole-algorithm (LF-MLFMA) based on spherical wave function expansions is advantageous to its high-frequency counterpart based on plane wave expansions. In the latter the depth of the tree is restricted by the smallest size of the leaf-level box size of 0.1λ making it inefficient at either low-frequencies or for problems with multi-scale features. The low-frequency MLFMA, however, has no limitation on the depth of the tree and allows for full-wave acceleration of Moment Method from DC to frequencies at which the models spans up to 120λ. Such broadband behaviour of the low-frequency MLFMA is made possible through construction of numerically stable translation operators for the spherical wave functions with orders reaching 180. This paper provides an overview of the algorithms allowing for stable high order translations of spherical functions. The LF-MLFMA accelerated Rao-Wilton-Glisson Moment Method utilizing one such algorithm is demonstrated in the frequency range from 1MHz to 2.5GHz for the problem of plane wave coupling to antennas onboard the F5 fighter jet at fixed discretization featuring 2 million surface elements.