Uma nova abordagem para a análise de arranjos de antenas com parâmetros aleatórios.

Abstract

This thesis presents a study for the problem of designing linear antenna arrays, as well as its applications on the performance improvement of mobile communication systems. Besides the classical methods, which are presented in an introductory way, to establish theoretical grounds for the topics that are treated in the following chapters, proposals for linear arrays, which have random parameters, are presented. Four new configurations for linear arrays are proposed. In the first proposed configuration, the distance d between the elements is fixed and the amplitude of the driving coefficients is modeled as a uniformly distributed random variable. In the second configuration, the driving amplitudes at the elements are fixed and the distance between them is chosen from an appropriate interval, this is, the distance is allowed to change between two given values, as a fraction of the wavelength. In the third case, the distance between the elements as well as the amplitude of the driving coefficients are chosen randomly. In the fourth configuration, the scanning array direction is taken at random. In this case, the main antenna beam randomly scans a certain space area around the antenna. For the first three configurations the standard ratio for the array factor was computed, and it provides an upper limit for the antenna radiation pattern. If the antenna parameters can be adequately chosen, one can show that those structures proved good radiation patterns. The other contributions from the thesis are proposals for the use of antenna arrays to improve the performance of communication links. On such example is the use of the circular array to cancel interference using subspace decomposition methods. Other contributions are the derivation of closed-form expressions for the computation of spatial correlation coefficients for the circular array, the derivation of closed-form expressions for the mutual interference power for the low-rank channel, the evaluation of the channel capacity, in terms of number of users, and the study of compact arrays for space diversity.