High Frequency Ground Wave Propagation

Electromagnetic ground wave propagation has been a topic of practical interest for broadcasting and underground prospection in the medium and lower radio frequencies for more than a century. A brief review of ground wave propagation and its development since the work of Zenneck and Sommerfeld a century ago is presented. Recently interest has been revived in using ground waves for wireless communication with remote under-populated areas using the high frequency (HF) range which extends from 3-30 MHz. We present numerical results for the fields excited by a vertical electric dipole (VED) on the earth´ surface in this range of frequencies and study the effect of ground conductivity on the received fields. In addition, we explore the possibility of using horizontal electric dipoles (HED) as transmitting and receiving dipoles. In this case, it is necessary to elevate both dipoles above the earth´s surface by a distance comparable to a wavelength in order to enhance the received signal level. This is practically feasible in the HF regime where the wavelengths are sufficiently short We conclude that elevated HED´s can perform as well as the VED, or even better, when the operating frequency lies in the upper end of the HF range.