Modeling and analysis of VHF wave propagation in forested environments
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A large proportion of the Earth's surface is covered by forests. The existence of trees results in a much higher propagation loss than that in free space for radio waves. Therefore, to improve the communication link in the forest is not only an important but also a challenging task for researchers. In this thesis, the Very High Frequency (VHF) radio wave propagation in the forest is studied. A forest can be described using an anisotropic slab model in this frequency band. The rigorous solution to the slab model is studied through a numerical implementation of the Sommerfeld integral. To reveal the propagation mechanisms, broadband data are generated and transformed into the time domain to identify the time-of-flight. To improve the computational efficiency and confirm the validity of the above full wave analysis, a ray optics solution and a 2D-Finite Difference Time Domain (FDTD) solution are implemented next. Further, comparisons with published measurement and simulation results are carried out to confirm both the simulation results and explanations of the propagation mechanisms in the forest.