Singularity-based modelling of antenna transient radiation processes

A singularity-expansion-method based approach is presented for the analysis of antenna transient radiation processes. Any time-domain electromagnetic field solver can be used to derive a minimal pole/residue spherical harmonic expansion of the equivalent currents excited on a suitable Huygens surface enclosing the antenna under analysis. In this way, the time-domain electromagnetic field radiated in the Fraunhofer region is evaluated analytically in terms of a newly introduced class of incomplete modified Bessel functions as the superposition of non-uniform spherical wave contributions attenuating along with the radial distance and time according to the real part of complex poles accounting for the natural resonant processes occurring in the structure.