Propagation effects for electromagnetic pulse transmission

Past research on the propagation of EM pulse signals over the surface of the earth is reviewed, with emphasis on analytical methods to predict waveforms. The overview begins with a flat-earth model that has the virtue of simplicity particularly when displacement currents in the earth are relatively small compared with the conduction currents. Here it is seen that the rise time of the ideally radiated step-function signal is of the order of a few microsec at a range of 50 km over average land paths. Such a prediction is in accord with published experimental data. At greater ranges, earth curvature comes into play, and various analytical and numerical methods can be used in overlapping time regions as a good consistency check. Other complicated effects such as mixed land-sea paths and ionospheric influences are also reviewed.