Short Wave Multipolar Antenna for Propagation by NVIS Effect
Palavras-chave:High frequency (HF), NVIS (Near Vertical Incidence Sky wave), ionosphere, communication, half-wave dipoles
ResumoThe objectives of this papper is to design, build and test an antenna resonant at the frequencies of 4, 5, 6, and 7 MHz, in the high frequency band (HF). With this antenna we want to explore and use NVIS (Near Vertical Incidence Sky wave), which consists in using the ionosphere as a reflector layer of sky waves, that reach the ionosphere with angles near vertical incidence. When reflected, these waves achieve distances from dozens to hundreds of kilometers for the established communication. For short distances, this technique is useful to surpass obstacles, such as those caused by rugged terrain between the terminals of the connection. The theoretical design of this antenna, which is composed by four half-wave dipoles, each one resonant at one of the given frequencies, was made. The parameters of the antenna and the radiation diagrams were obtained by using an antenna simulation tool. Since the ionsphere is used as a reflective layer of skywaves that arrive from the antenna, the propagation in the ionosphere was also studied. The antenna was then built and tested, and a good accordance between theoretical and experimental results was achieved.