Abstract :
The paper contains curves from which the reflection coefficient at the Earth´s surface for radio waves of any state of polarization can be determined for angles of incidence greater than 80°. It is pointed out that the ray theory, on which the reflection from a reflector is assumed to be equal to the radiation from an image of the transmitting aerial in the reflecting surface, is not applicable at grazing incidence unless the heights of the transmitting and receiving aerials are comparable with the wavelength. From an analysis given by Norton, however, it is deduced that, when the ray theory does not apply, the field at the receiver is equal in most practical cases to the vector addition of two fields, one that given by the ray theory, and the other, which corresponds to the Sommerfeld surface wave, having a magnitude dependent on the electrical properties of the reflector and the distance between transmitter and receiver but independent of the heights of transmitter and receiver. The ratio of the magnitudes of the surface wave to image fields is much less for horizontally than for vertically polarized waves, so that the ray theory is applicable over a wider range of angles of incidence for horizontally than for vertically polarized waves.
