Análise, projeto e concepção de um elemento irradiador quase-isotrópico em 3D.

Abstract

This master dissertation work deals the analysis, design and conception of a quasi–isotropic radiator. It is introduced the theoretical formulation needed in the design of wire antennas and some basic parameters. In this part, the theory is used in the dipole design with isotropic characteristics. The short and Hertz dipole are highlight because they are used in the quasiisotropic radiator development. A three-dimensional radiator model is made by means of commercial software simulations. Two radiators models are analyzed: the first one with bidimensional quasi-isotropic characteristics, named bended dipole, and the other, named double arc dipole, with three-dimensional characteristics. It is evidenced that 3D radiator model presents a better isotropic radiating with linear polarizations in all directions. For this model the behavior of the current distribution throughout the conductor is presented. In the radiator analytical model the structure was divided into five discrete elements. This way facilitates the deduction of the approached analytical equations for the far fields in each element separately. After that it is made the vectorial sum of each element to obtain the total field. With satisfactory results in the simulation the antenna was built to operate in the frequency of 2.45 GHz. Two options to match the antenna and transmission line are used. The better matching happens with wideband tapered Balun, where the multiple resonance in the presence of ¼ λ balun are removed. The experimental results for two prototype models, compared with the analytical approximation and simulation, are presented and had revealed a good agreement with the theoretical forecast.