Sistemas de controle e conformação de diagrama de irradiação para redes de antenas

Abstract

This work describes the design and test of phase-shifters and attenuator to operate in the microwaves range. The document starts with the presentation of the main motivations for this work. Then, the results of a literature survey about phase-shifter topologies is presented. In chapter 3, attenuators and phase-shifters with four-bit control signals are presented. These devices were initially designed considering their integration into a nano-satellite that operates at 2.26 GHz. Two topologies of attenuators have been tested: one with T-shape and another with Π-shape. The design of such devices has been achieved by considering the scattering parameters (S-matrix). The phase-shifters were designed in two configurations: with switchable transmission lines, based on the propagation delay, and another based on high-pass and low-pass passive filters, which have been used to synthesize a transmission line with the T and Π circuits composed of lumped LC elements. The fabricated attenuators as well as the phase-shifters exhibited similar behavior than the theoretical models for most of the control states. The phase-shifter topology with the best performance was the one based on switchable transmission lines, since it was not possible to control completely th variability of the parameters of the lumped LC components in the design frequency. Finally, a linear antenna array has been considered for wireless local area networks. In order to allow this antenna to steer the main beam electronically whilst controlling the side lobe levels simultaneously, the phase-shifter based on switchable transmission lines has been optimized for operation at 2.4 GHz. In order to assess the performance of this antenna array under different beamforming situations, an heuristic based on the firefly algorithm has been used to generate a computer code. This tool has been employed to demonstrate that it is possible to steer the main beam in an angular region larger than 50◦ whilst still keeping the side lobe levels 20 dB below the level of the main beam.