Dominant lateral waves in the canopy layer of a four-layered forest

Abstract

In this paper a forest model of four-layered geometry is utilized for the theoretical analysis of radio wave propagation characteristics in the forest environment. Differing from those reported in previous publications, the current paper considers a receiving antenna that is located in the forest canopy layer instead of the trunk layer, and hence the results presented are not available elsewhere. Dyadic Green's functions in their eigenfunction expansion forms for the four-layered geometry are used at first to obtain an exact integral representation of the radiated electric field in the canopy layer. The radiated electric field components due to an arbitrarily oriented, small dipole in the trunk layer are then evaluated using the saddle point technique and the branch cut integrations, leading to closed-form expressions for the field. The total field is found to consist of the direct, the reflected, and the lateral waves. Although both the lateral waves propagating along the air-canopy and the trunk-ground interfaces play an important role in the propagation mechanism, only the lateral wave along the air-canopy upper interface dominates the total field in the far zone. Path loss of the radio waves in the forest is computed numerically for both the vertically and the horizontally oriented dipoles.