Abstract :
The paper relates to the theory in which the propagation of vlf radio waves is treated by regarding the space between the earth and the ionosphere as a waveguide. Its purpose is to answer some criticisms of earlier papers by Budden. The earth is assumed to be a perfectly conducting plane, and the ionosphere is assumed to be a homogeneous medium with a sharp boundary. In general, there is no unique way of assigning numbers to the waveguide modes. The numbers are usually assigned by continuity with the case where the ionosphere is a perfect conductor, but this method fails for some values of the height and the conductivity. If the product of the height and the conductivity is less than a certain critical value, the attenuation for the zero order mode has a maximum at some frequency, and thereafter decreases as the frequency increases, as was found by Budden. If the critical value is exceeded, the attenuation for the zero order mode increases indefinitely with increasing frequency, as was found by Wait and Liebermann.
