Τεχνικές διαμόρφωσης διαγράμματος ακτινοβολίας για συχνοτικά και χωρικά ευρυζωνικά συστήματα στοιχειοκεραιών
KeywordsΣτοιχειοκεραία ; Δίαυλος ; Μορφοποίηση διαγράμματος ακτινοβολίας ; Βάρη ; Συστήματα στενής ζώνης ; Συστήματα ευρείας ζώνης ; Beam squint
Despite the fact that the Telecommunications and Computer Networks are relatively new fields, they have been growing tremendously over the past few years and the technological steps that have been made are enormous. Nowadays, due to the increased use of new wireless communication systems, the need to develop new tools and techniques, in order to optimize the performance in a plethora of new and different scenarios with the restrictions they impose, is considered necessary. One technique is the shaping of the beam pattern of array antennas so that the users are more efficiently served by increasing the SNR ratio. Moreover, the number of users can be increased by creating many radiation lobes and adjusting each one to a different user. In the presented study different models and beamforming techniques were examined and introduced for a wide range of different scenarios and requirements. More specifically, at the beginning of this dissertation, its purpose is clearly introduced and the requirements that need to be satisfied of the new generation networks are analyzed. Subsequently, the main features, difficulties and restrictions that the wireless propagation environment sets are referred as it is a fact that this should be seriously taken into account when a system is being designed. The following chapters aim to present the different beamforming techniques and the challenges that emerge depending on the requirements of both the signal bandwidth and the antenna size, factors that play a major role during the phase of system design. To conclude, it should be noted that that the main emphasis in this dissertation is given to the phenomena created due to the spatial and frequency wideband transmission as the coexistence of these two system characteristics causes intense changes in the radiation pattern of the antenna array and requires special handling techniques.