Microwavelmillimeter-wave propagation in woods and forests was investigated at 9.6, 28.8, and 57.6 GHz. In order to perform the measurements under well defined, reproducible conditions, a regularly planted, well groomed stand of trees of about the same growth (pecan orchard near Wichita Fails, TX) was chosen as the test site. The experiments were repeated, over the same transmission paths, under both summer and winter conditions, i.e., with trees in leaf and without leaves. Of particular interest were the range dependence, beam broadening, and depolarization of millimeter-wave beams in vegetation and the frequency dependence of these effects. The experiments have shown, in particular, that the range dependence is characterized by a high attenuation rate at short vegetation depths and a reduced attenuation rate at large depth. For trees fully in leaf, the transition between the two regimes can be rather abrupt and the change in attenuation rate substantial. Just after the transition significant beam broadening (and depolarization) occurs. A theory of millimeter-wave propagation in vegetation was derived using transport theory. Theoretical and experimental results are in good qualitative agreement; both show the same trends. The theory explains these trends in terms of the interplay between the coherent (direct path) field component and the incoherent (multiscattered) field component. Achieving good quantitative agreement will require further refinement of the theory.
Measurements on point-to-point transmission at street level were performed in downtown Denver, CO, with RF probes that operated in the upper microwave and lower millimeter-wave bands. All probes were mounted on self-contained vehicles, thus permitting a variety of path scenarios. Information on performance of SHF/EHF channels when propagating in an urban environment on both line-ofsight and non-line-of-sight paths is presented.
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