Influence of branch geometry on radiation field characteristics from lightning return strokes in the time domain

Due to the disappearance of the geometric symmetry produced by the branches of the lightning channel, the characteristic of the radiation field is analyzed in 3-D rectangular coordinates using the FDTD method. Generalized perfectly matched layer (GMPL) is adopted in the underground to calculate absorbing boundary region with the finite conductivity of the ground. The results show that the effect of branch is to introduce free structure into the time-domain radiation field waveform and consequently to increase the higher-frequency content. Furthermore the relationship between the fractal dimension and space orientation and relative position from the main channel and the generated EM fields in the time domain is also discussed in detail.