Developments in the transmission-line modelling method for electromagnetic compatibility studies
The transmission-line modelling (TLM) method is applied to 3-dimensional problems in electromagnetic compatibility (EMC). The method is found to be a versatile tool which is ideally suited to the modelling of many EMC systems. A new way of deriving the scattering properties of the TLM node is presented and the derivation of mesh parameters, the application of boundary conditions and methods of applying excitation and of taking outputs are described. Issues regarding the efficient implementation of the TLM algorithm and a way of running very large simulations are reported. A multigrid method is introduced which allows meshes of different resolutions to be connected together to form a complete system. The method is used to apply fine resolution only in areas where it is required and to move numerical boundaries away from the region of interest. Comparisons are made with the more traditional graded mesh technique, using the hybrid node. Results are presented for a number of different systems with particular emphasis on the environment in which radiated emission tests are undertaken, although more general systems are also considered. The consequences of making measurements in an unlined screened room are discussed and ways of damping resonances are investigated. Wire, slot and spherical dipole antennas are modelled. Field-to-wire coupling, the TEM cell, a simplified device under test, the shielding properties of a vehicle body and the current induced by a simplified table-top device are also considered. Techniques are developed to obtain the Q factor of a screened room loaded with radiation absorbing material (RAM) and to obtain the radiation resistance of an antenna in free-space and also in close proximity to conducting surfaces.