Several applications of UWB technology have been recently proposed for communications, radar, precise positioning and tracking. The extremely large bandwidths of the systems encourage the use of time-domain formulations. In particular, the objective of this research activity has been to develop efficient methods for the transient characterization of pulsed arrays. Pulsed arrays consist of an arrangement of Ultra-Wideband antennas sourced by baseband carrier-free input signals, showing pretty different radiating performances with respect to narrowband arrays. Tools for the complete transient characterization of pulsed arrays require the efficient analysis of the isolated radiating elements that constitute the array, the analysis of the effects of the couplings on the radiating performances of the array and the synthesis of their transient excitations to realize a desired far field of the array. Each of these topics has been reported in this thesis. Suitable representations of signals and electromagnetic fields to efficiently characterize UWB sensors are presented. In particular, two techniques for the efficient modeling of radiating elements by means of suitable spatial and temporal expansions are introduced. One technique is suitable for aperture antennas, the other for antennas of more general shape, such as UWB dipoles, TEM horn and non canonical-aperture horns. These expansions permit to capture the complete spatial and temporal behavior of the antenna (its effective height) by a small set of parameters thus expressing its response by semi-analytical representations. The proposed techniques are suited to strengthen any existing time-domain numerical solver and to perform more easily UWB array analysis and synthesis. A simple physical model of the time domain coupling for UWB arrays is proposed, aimed to identify the role of the scan angle, input signal duration, repetition rate of the input pulse train and impulse response of the single antenna. Expressions for the time domain active array and element patterns are retrieved and an investigation on coupling echoes and their distorting effect on the main signal permits to obtain conditions to reduce coupling even in compact configurations with very small inter-element distances. Finally a synthesis technique to compute the amplitude, the transient behavior and the relative delay of the input signals of UWB arrays is presented in order to shape the radiated field in accordance to a given mask in the angular and temporal domains. The technique extends the method of alternating projections to the time domain array synthesis: in particular it consists of iterative projections of the radiated pattern onto the desired pattern mask and of the obtained excitations onto a physical set of excitations. Thanks to this second projection, the proposed technique provides input currents which are physically realizable by means of a beamforming network which will be shown in the chapter. Each topic is developed presenting a theoretical section and some numerical examples to validate methods and investigate the phenomena, followed by some discussions on the results.
Ciattaglia, M. (2008). Modeling and design of ultra-wideband arrays.
|Titolo:||Modeling and design of ultra-wideband arrays|
|Data di pubblicazione:||14-mag-2008|
|Anno Accademico:||A.A. 2005/2006|
|Tipologia:||Tesi di dottorato|
|Citazione:||Ciattaglia, M. (2008). Modeling and design of ultra-wideband arrays.|
|Appare nelle tipologie:||07 - Tesi di dottorato|
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