This dissertation presents the contributions and the research conducted in developing and implementing Microwave Tomography (MWT) systems. MWT is an imaging modality which aims to interrogate an object of interest by microwave energy, and quantitatively “find” the interior spatial distribution of its dielectric properties using field measurements taken outside the object. Due to the inherent non-linearity of the MWT problem, a substantial amount of electromagnetic scattering data is required to ensure a robust inversion and quantitatively accurate imaging results. This research benefits a variety of applications including biomedical imaging, industrial non-destructive testing, and security applications. Developing a MWT system, requires many critical components including the bandwidth and polarization purity of the collected fields as well as calibration of the fields scattered by the object of interest. Two generations of MWT systems were designed, implemented, calibrated and tested at the University of Manitoba (UM). These systems aim different approaches for near-field measurements which are referred to as the direct and indirect methods. With regard to the antenna design, a novel methodology applicable to broadband planar antennas is introduced. This technique is based on a combination of field modelling, herein, the finite element method and transmission line modelling. In the first generation of the UM MWT systems, a suitable antenna system was utilized. The system under study was a prototype, where twenty-four co-resident antennas encircle the object of interest to directly measure the fields. In the second generation of the UM MWT systems, the feasibility of using a novel technique to indirectly measure the fields by a secondary array of near-field scatterer probes was studied. The technique is based on the Modulated Scatterer Technique (MST). In this system, antennas are called ``collectors", since the role of antennas are changed to collecting probes' scattered fields. A number of PIN diodes were utilized to activate the probes. Finally, the capability of the probe system was investigated and its performance with the previously constructed tomography systems was compared. Various dielectric phantoms were utilized to test the accuracy of the systems.

This dissertation presents the contributions and the research conducted in developing and implementing Microwave Tomography (MWT) systems. MWT is an imaging modality which aims to interrogate an object of interest by microwave energy, and quantitatively “find” the interior spatial distribution of its dielectric properties using field measurements taken outside the object. Due to the inherent non-linearity of the MWT problem, a substantial amount of electromagnetic scattering data is required to ensure a robust inversion and quantitatively accurate imaging results. This research benefits a variety of applications including biomedical imaging, industrial non-destructive testing, and security applications. Developing a MWT system, requires many critical components including the bandwidth and polarization purity of the collected fields as well as calibration of the fields scattered by the object of interest. Two generations of MWT systems were designed, implemented, calibrated and tested at the University of Manitoba (UM). These systems aim different approaches for near-field measurements which are referred to as the direct and indirect methods. With regard to the antenna design, a novel methodology applicable to broadband planar antennas is introduced. This technique is based on a combination of field modelling, herein, the finite element method and transmission line modelling. In the first generation of the UM MWT systems, a suitable antenna system was utilized. The system under study was a prototype, where twenty-four co-resident antennas encircle the object of interest to directly measure the fields. In the second generation of the UM MWT systems, the feasibility of using a novel technique to indirectly measure the fields by a secondary array of near-field scatterer probes was studied. The technique is based on the Modulated Scatterer Technique (MST). In this system, antennas are called ``collectors", since the role of antennas are changed to collecting probes' scattered fields. A number of PIN diodes were utilized to activate the probes. Finally, the capability of the probe system was investigated and its performance with the previously constructed tomography systems was compared. Various dielectric phantoms were utilized to test the accuracy of the systems.

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De nombreuses applications civiles et militaires (faisceaux hertziens, futurs réseaux mobiles, communications par satellite, radars automobiles, systèmes d’imagerie haute résolution) nécessitent des antennes à faisceau reconfigurable (dépointage de faisceau, faisceaux multiples, faisceaux formés). Les antennes à réseaux transmetteurs apparaissent comme une alternative aux réseaux phasés classiques ou aux réseaux réflecteurs pour ces applications. L’objectif principal de cette thèse est de démontrer la faisabilité de réseaux reconfigurables fabriqués avec des technologies standards en bande Ka (20-30 GHz). Divers cellules élémentaires utilisant des diodes p-i-n et fonctionnant en polarisation linéaire ou circulaire ont été conçues, optimisées et caractérisées. Les mesures en guide d’onde montrent des pertes minimales de 1,09 dB à 29,0 GHz et une bande passante à 3 dB de 14,7%. Une méthode de simulation hybride a été développée afin d’analyser efficacement des réseaux de grandes dimensions utilisant des rotations séquentielles d’éléments pour optimiser la qualité de polarisation et les diagrammes de rayonnement. Un réseau de 400 cellules élémentaires fonctionnant en polarisation circulaire a été réalisé et testé en chambre anéchoïque. Un dépointage électronique de ±60° et la possibilité de commuter entre les deux polarisations circulaires (droite/gauche) ont été démontrés. / Several civil and military applications (hertzian beams, satellite communications, automotive radars, high resolution imaging systems) require antennas with reconfigurable beam capabilities (beam-scanning, beamshaping, multiple beam generation). Transmitarray antennas are good candidates and represent an alternative to classical phased arrays or reflect-arrays for these applications. The main objective of this thesis is to demonstrate the feasibility of reconfigurable transmitarrays fabricated with standard technologies in Ka-band (20-30 GHz). Different unit-cell designs based on p-i-n diodes have been developed to work in linear and circular polarization. Their optimization and experimental characterization have been performed. Waveguide measurements show insertion losses of 1.09 dB at 29.0 GHz with a 3-dB bandwidth of 14.7%. A hybrid simulation technique has been developed in order to analyze efficiently large transmitarrays in which the sequential rotation technique has been applied to optimize the polarization quality and the radiation patterns. A 400-elements transmitarray operating in circular polarization has been realized and tested in anechoic chamber. A beam-scanning angular coverage of ±60° and circular polarization selection (left/right) have been demonstrated.