Modelo semi-empírico de predição de cobertura na faixa de VHF para ambientes de propagação em regiões com vegetação

Abstract

The main objective of this research is to analyze the behavior of the radios signal deviation through forests with medium vegetation, on VHF band, having some typical Amazon Forests vegetation as background. In that purpose, measurements campaigns were done inside two forests: the first region with the equivalent of a rubber tree vegetation, inside Cidadãos Park in Belém/PA, near the campus of the Technology Institute IT of the Federal University of Pará UFPA; The second one is inside a Brazil nut tree region, in Manaus/AM, at the East Zone Campus CZL, of the Federal Institution of Education, Science and Technology of Amazonas IFAM. Both forests have the agreeable aspects for the development of the research for having their landscape shapes considered as plane and the trees have rounded trunks with heights above 20 m, which leaves are grouped at the top of the stems, making the radio signal flow possible, irradiated and received by antennas set under the trees crown, sending and receiving signals with the wavelength of about one meter, that runs the path around the tree trunks and spanning throughout the forest. The methodology used in both of the measurement campaigns was done on setting a communication system inside the forest with the transmitter module kept still, while the receptor module, placed behind a tree and put in the same alignment as the transmitter module, had the power of the received signal measured and registered. Nearly after, the receptor module was moved to the next preset measurement point, and those actions went on until they reach the maximum point of distance possible between the transmitter and receptor modules. The experimental data gathered on the measurement campaigns were computationally implemented and it was established the formulation of semi empirical models for medium density vegetation environments here studied. The research proved that the propagation of the radiolectric signal through this vegetation, on a flat shaped land, admitting that the elements of the radiation system are placed inside the forest, under the tree crowns and working at the frequency of VHF band, with wavelengths of about a meter, the biggest obstacles for the propagation of these signals, also considering the loss on free space, are the tree trunks. With this wavelength, the signal lose power on stems, but also outlines them according to the power applied on the transmitter, being able to spread for long distances.