Excitation of guided v.l.f. modes below a lossless anisotropic ionosphere

The excitation efficiencies due to a magnetic line source of the first four vertically polarised guided modes below a lossless sharply bounded ionosphere are investigated, for the case of propagation transverse to the external magnetic field. It is found that the n = 0 mode is essentially a surface wave guided by the ionosphere/free-space boundary. Also, the results show that, for a source near the ionosphere boundary, the excitation of the n = 0 mode can be several orders higher than that of the n = 1 mode, even at the higher end of the v.l.f. range, with the result that the n = 0 mode can become important in the guidance of energy at the higher end of the v.l.f. band for considerable distances from the source compared with that of the n = 1 mode.