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Controlo do diagrama de radiação em meios com desvanecimento
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Abstract(s)
O principal objetivo desta dissertação de mestrado foi o estudo de várias soluções de modo a controlar o diagrama de radiação de um agrupamento de antenas em meios com desvanecimento. Inicialmente obtiveram-se os parâmetros essenciais das antenas utilizadas, nomeadamente o diagrama de radiação e o ganho. Desenvolveu-se um sistema para medir os diagramas de radiação de forma automática e com uma resolução abaixo de 2º através de um servo motor. Uma aplicação implementada em MatLab realiza o controlo do motor e desenha o diagrama de radiação em tempo real.
Para as medições realizadas na câmara anecoica, bem como para as medições de propagação do sinal no meio com vegetação, desenvolveu-se um sistema que interliga a antena recetora com o computador portátil de forma a obter os valores de potência do analisador de espetro.
Tendo-se o conhecimento dos parâmetros das antenas, realizaram-se as medições no meio com vegetação, caracterizado por troncos e folhas no percurso da propagação do sinal. Foram realizadas medições para 5 distâncias diferentes 20, 40, 60, 80 e 100 metros com ganhos a variar desde os 3 até os 15,6 dBi. As medições foram realizadas com uma antena monopolo como emissora para uma frequência de 2,42 GHz.
Através dos resultados obtidos aferiu-se um aumento da atenuação à medida que se passa por meios mais obstruídos, sendo que para a distância de 20 metros os diagramas obtidos aproximam-se aos diagramas obtidos na situação de espaço livre. Também verificou-se para as distâncias de 60, 80 e 100 metros um grande aumento da atenuação à medida que o ganho da antena recetora aumenta. Desta forma, o melhor tipo de antena para estas distâncias podem ser as antenas omnidirecionais devido a que conseguem receber maior potência em relação às antenas diretivas.
Foram estudadas várias topologias de deslocadores de fase, bem como algumas soluções que derivam da mesma. De modo a controlar o diagrama de radiação desenvolveu-se um sistema de comunicação mecânico e um eletrónico, para uma frequência de operação de 2,42 GHz. O sistema de comunicação mecânico é constituído para um motor de passo e uma antena suspensa, sendo o controlo do mesmo realizado através de um microcontrolador. O sistema de comunicação eletrónico é constituído por um agrupamento de 4 antenas suspensas ligadas a uma malha de alimentação. O estado de ativação de cada antena é realizado através de díodos PIN os quais são controlados por um microcontrolador. Os sistemas foram testados de forma a avaliar o seu desempenho, sendo que o sistema mecânico apresentou menor perdas de inserção em relação ao sistema eletrónico.
The main objective of this master's thesis was the study of various solutions in order to control the radiation pattern of an antenna array in environments with fading. Initially it was obtained the essential parameters of the used antennas, namely the radiation pattern and the gain. It was developed a system capable of automatically measuring the radiation pattern using a servo motor. An application implemented in MatLab performs the control of the engine and draws the radiation pattern in real time. For measurements performed in an anechoic chamber as well as the signal propagation in environments with vegetation, a system was developed to connect the receiver antenna with the laptop in order to obtain the power values of the spectrum analyzer. Having the knowledge of the parameters of the antennas it was held measurements in environment with vegetation characterized by trunks and leaves the in order to chick the propagation signal path. Measurements were performed for five different distances 20, 40, 60, 80 and 100 meters with gain varying from 3 to 15,6 dBi. Measurements were made with a monopole antenna and emitting at a frequency of 2,42 GHz The results obtained showed an increase of attenuation as it passes through more clogged environment, and for the 20 meters distance the diagrams obtained are similar to the diagrams obtained in the free space situation. Also it appears that for the distances of 60, 80 and 100 meters a large attenuation increase as the gain of the receiver antenna increases. Thus, the best type of antennas is the omnidirectional because they can receive more power in relation to the directive antennas. Various topologies of phase shifters were studied and some solutions were derived. In order to control the radiation pattern it was developed a mechanical and an electronic communication system, for the 2,42 GHz frequency. The mechanical communication system is constituted by a step motor and a suspended antenna, and its control is performed by a microcontroller. The electronic communication system comprises four suspended antennas connected to a power grid. Each antenna activation state is accomplished by PIN diodes which are controlled by a microcontroller. The systems were tested to assess their performance, and the mechanical system presented lower insertion losses in relation to the electronic system.
The main objective of this master's thesis was the study of various solutions in order to control the radiation pattern of an antenna array in environments with fading. Initially it was obtained the essential parameters of the used antennas, namely the radiation pattern and the gain. It was developed a system capable of automatically measuring the radiation pattern using a servo motor. An application implemented in MatLab performs the control of the engine and draws the radiation pattern in real time. For measurements performed in an anechoic chamber as well as the signal propagation in environments with vegetation, a system was developed to connect the receiver antenna with the laptop in order to obtain the power values of the spectrum analyzer. Having the knowledge of the parameters of the antennas it was held measurements in environment with vegetation characterized by trunks and leaves the in order to chick the propagation signal path. Measurements were performed for five different distances 20, 40, 60, 80 and 100 meters with gain varying from 3 to 15,6 dBi. Measurements were made with a monopole antenna and emitting at a frequency of 2,42 GHz The results obtained showed an increase of attenuation as it passes through more clogged environment, and for the 20 meters distance the diagrams obtained are similar to the diagrams obtained in the free space situation. Also it appears that for the distances of 60, 80 and 100 meters a large attenuation increase as the gain of the receiver antenna increases. Thus, the best type of antennas is the omnidirectional because they can receive more power in relation to the directive antennas. Various topologies of phase shifters were studied and some solutions were derived. In order to control the radiation pattern it was developed a mechanical and an electronic communication system, for the 2,42 GHz frequency. The mechanical communication system is constituted by a step motor and a suspended antenna, and its control is performed by a microcontroller. The electronic communication system comprises four suspended antennas connected to a power grid. Each antenna activation state is accomplished by PIN diodes which are controlled by a microcontroller. The systems were tested to assess their performance, and the mechanical system presented lower insertion losses in relation to the electronic system.
Description
Keywords
Propagação do sinal Ganho Diagrama de radiação Deslocadores de fase Malha de alimentação Signal propagation Gain Radiation pattern Phase shifters Power mesh Engenharia Eletrotécnica - Telecomunicações . Faculdade de Ciências Exatas e da Engenharia