Análise paramétrica de antenas log-periódicas lineares e com fractal de Koch

Abstract

In this work, the Koch fractal is used to reduce the overall size of printed log-periodic antennas that operate in both WLAN (2.4 GHz) and WiMAX (5.8 GHz) frequency bands. The main goal is to develop an antenna reduced in size whilst keeping nearly the same electromagnetic properties of conventional log-periodic antennas. The first step in this development was the design of a printed log-periodic antenna by modelling the structure in the electromagnetic simulation Ansys HFSS. A detailed study about the transition between the coaxial cable used to feed the antenna and the printed structure has been carried out. The investigations showed that this is a critical issue of the antenna design, especially concerning the higher part of the operation band. The second part of the present work was the development of a dual-band antenna based on the log-periodic topology. This has been achieved by removing one dipole and by making small geometrical changes in the antenna developed in the first part. In order to reduce the overall antenna dimensions, fractal geometries have been studied. Among the analyzed cases, the Koch fractal has been chosen due to the ease of implementation. The two first iterations have been applied to the conventional log-periodic antenna. By increasing the order of the Koch fractal, the global antenna dimensions could be reduced whilst keeping nearly the same electromagnetic properties. A prototype with the first iteration has been designed and modelled in ANSYS HFSS. All the desinged antennas have been fabricated and measured in the Laboratório of Electromagnetics, Microwaves and Antennas (LEMA) of UNIPAMPA, so as to allow validating the simulation results. The main challenges faced during the fabrication of the prototypes are also described at the end of this document.