This thesis describes a theoretical and experimental investigation of wireless energy transfer between high-Q resonant radiofrequency (RF) oscillators. A model used by Kurs \emph{et al} \cite{Kurs_original} was recast in a form which enabled expression of the results in terms of measurable electrical quantities. This model was tested using circular resonant copper loop antennas at a frequency near 10 MHz. Accurate calculation of the mutual inductance between loops was required in order to predict the loop coupling parameters, and was carried out using a custom-written computer code. Two resonant loop antenna RF oscillators were first used to check that the model predictions were accurate in the two-oscillator case. Based on the success of these tests, the model was extended to the case of three oscillators in two different configurations, the first having two receiving oscillators, and the second having two transmitting oscillators. Model predictions for both configurations were experimentally tested over a range of coil separations and angular inclinations. These experimental tests confirmed the model's applicability in the three-oscillator regime, with significant deviations from the model only being observed when any pair of loops was in very close proximity (i.e. when the separation of loop centers was comparable to the loop diameter). This may have been be due to either nonlinear dielectric losses (due to large amplitude RF electric fields) spoiling the Quality factors Q of the loop antenna resonators, or to increased capacitive coupling between loops at short distances (not included in the current model), or both. Further investigation would be required to definitively establish the origin of the deviation from the model at short distances, but from an engineering point of view accurate modelling of the performance in the "close loop" regime is not critical since the primary purpose of wireless power transfer is to transmit power over a reasonable distance.

De nouveaux besoins dans le domaine des télécommunications par satellite ont amené les industriels du secteur à se pencher sur l’optimisation des ressources en créant des systèmes reconfigurables, capables d’adapter leur fonctionnement fréquentiel en cours de mission. Cette thèse s’intéresse plus particulièrement aux multiplexeurs et à la manière de les rendre agiles à travers les filtres qui les composent ainsi qu’une adaptation de leur architecture.Dans un premier temps, le présent manuscrit dresse l’état de l’art des dispositifs accordables réalisés par les équipes de recherche du monde entier, avant de proposer des solutions mettant en œuvre une topologie de multiplexage à coupleurs hybrides. Dans un second temps, des études sont présentées portant sur une pluralité de concepts de cavités ou d’éléments de couplage accordables. Certains de ces concepts sont ensuite sélectionnés et assemblés afin de former des fonctions de filtrage et de multiplexage accordables. La dernière partie présente ainsi deux multiplexeurs accordables, l’un permettant une reconfiguration en bande étroite, l’autre en bande large, le premier ayant donné lieu à une réalisation expérimentale. / New needs in the field of satellite telecommunications have led manufacturers in the sector to focus on optimizing resources by creating reconfigurable systems able to adapt their operating frequencyplan during the mission. This thesis focuses on multiplexers and how to make them agile through their architecture and the filters that compose them.This manuscript starts by realizing the state of the art oftunable filtering devices through analysis of contributions made by research teams around the world. Based on this state of art,solutions to the problematic are proposed using a hybrid coupler multiplexing topology. Then studies are presented on various tunable cavities or coupling elements concepts. Some of these concepts have been selected and assembled to form tunable filtering and multiplexing functions. The last part thus presents two tunable multiplexers, allowing narrowband or broadband reconfiguration. An experimental realization has also been conducted on the narrowband version.

No / A new dual-log spiral geometry is proposed for microstrip resonators, offering substantial advantages in performance and size reduction at subgigahertz frequencies when realized in superconducting materials. The spiral is logarithmic in line spacing and width such that the width of the spiral line increases smoothly with the increase of the current density, reaching its maximum where the current density is maximum (in its center for ¿/2 resonators). Preliminary results of such a logarithmic ten-turn (2 × 5 turns) spiral, realized with double-sided YBCO thin film, showed a Q.-factor seven times higher than that of a single ten-turn uniform spiral made of YBCO thin film and 64 times higher than a copper counterpart. The insertion loss of the YBCO dual log-spiral has a high degree of independence of the input power in comparison with a uniform Archimedian spiral, increasing by only 2.5% for a 30-dBm increase of the input power, compared with nearly 31% for the uniform spiral. A simple approximate method, developed for prediction of the resonant frequency of the new resonators, shows a good agreement with the test results.