Field on Ground Excited by VLF Vertical Electric Dipole in Horizontal Stratified Nonuniform Ionosphere

The spaceborne VLF transmitting antenna is idealized as a vertical electric dipole. According to the model of the horizontal stratified nonuniform ionosphere, it has been analyzed and calculated. The magnetic field intensity can be obtained by the Fourier inversion to the wave spectral intensity of the field. The fast Fourier transform method is more correct than the quasi longitudinal approximation method. The calculation results are drawn as follows. First, when the VLF wave arrives at the lower boundary of the ionosphere, it can only pass through the boundary between the air and the ionosphere and continue to propagate for the wave beam of close to vertical downwards propagation. However, the majorities of wave beams are reflected on the boundary, which has the significant inclination angles. Second, the VLF vertical electric dipole antenna laying at the ionosphere can efficiently emit the electromagnetic wave. It can pass through the ionosphere and the air to arrive at the sea surface, and is received. Third, because the D layer of the ionosphere exists at day, and the attenuation of the magnetic field intensity is bigger, so the signal can easily be received at night.