Influência da geometria dos elementos metálicos na miniaturização de condutores magnéticos artificiais com aplicações em antenas

Abstract

This thesis addresses the study of artificial magnetic conductors (AMC) without vias for antennas applications. The results are supported by the commercial program COMSOL MULTIPHYSICS, a finite element software. This work is divided into two steps: first, it is evaluated how the metal inclusions geometry modify the AMC resonant frequency; and second, coupling effects between the antenna and AMC due to different geometric shapes for AMC metallic inclusions are studied. In the first stage, different geometric forms were analyzed. As a contribution, it was observed that the reduction in the resonant frequency of the AMC is associated with the increase in the effective length of the metallic inclusions, provided that this increase in effective length occurs in the same direction of incidente wave polarization. Based on this observation, the meander line geometry was studied and compared to a square patch, used as a reference. In this context, another contribution refers to the observation of a reduction in the ratio between the first and second AMC resonant frequency and the appearance of different operating bands, depending on the number of meanders used. Similarly, when using meander line geometry in a frequency selective surfaces metallic patch, the miniaturization and the appearance of different operating bands were also observed. In the second part of this work, a study on the interaction between antennas and AMC is developed. Two antennas are evaluated, a dipole and a bowtie. For the AMC ground plane, four geometries are analyzed, including the square, circular, bowtie and the U-shape. The unit cells are designed for the same operating frequency. In this step, as contribution, it was observed that, due to the shape of the metallic patch, the direction of the maximum gain in the H plane can be rotated. In addition, an improvement in the half-power beam (HPBW) of the antenna is reported. Further, the gain, HPBW and the front-back ratio depend on the antenna position over the AMC and the number of unit cells present in the AMC array. The results suggest that a careful choice of conductor element geometry in an AMC for antenna applications is of paramount importance. Keywords: Antennas, artificial magnetic conductors, metamaterials, metasurfaces, surface selectives frequency.