VHF field intensities in the diffraction zone

For the past few years there has been a general interest in the mechanism of propagation of vhf waves in the diffraction zone. Several theories have been advanced which attempt to describe the phenomena quantitatively, however, most calculated results from these theories have yielded signal strengths several decibels below those obtained experimentally. This analysis follows the general procedure of obtaining a solution to the wave equation, subject to the appropriate boundary conditions. In obtaining this solution, it is necessary to make some assumption regarding the distribution of the refractive index as a function of the height above the surface of the earth. The essential difference between this solution and those previously presented is the form of this variation. An exponential form which approaches unity at large heights has been chosen. Using this distribution, an expression for the field strength as a function of separation between the transmitting and receiving antennas and the height of the antennas above the earth is obtained and signal strengths are calculated for comparison with measured values.