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With the multiplication of radiating sources in our environment, we are witnessing the development of technical means to test, measure and visualize the electromagnetic field. This demand from industry has led to the development of various field imaging technologies and different approaches have been proposed, most of which are based on scanning processes of a point probe. They will be briefly presented in this thesis. There are also more original solutions using optical methods to visualize the field. Within ONERA, the choice was made more than 20 years ago to develop an infrared thermography method allowing the characterization of the electric field (EMIR: ElectroMagnetic InfraRed). Improvements made to this method, including lock-in modulation, have made it quantitative. More recently this technique has been adapted to the visualization of the magnetic field. However, these high performance infrared cameras are very expensive (several tens of thousands of euros). The idea of a thermography in the visible, with a simple sCMOS camera, was naturally born: moving from the infrared to the visible domain allows a substantial saving on the camera cost, with equivalent resolution and dynamics, or even higher. But the transition between infrared and visible requires to make "visible" a heating. One way to make this transition is to exploit the thermofluorescent properties of some fluorophores, whose fluorescence depends precisely on temperature.For this we build on previous work on infrared thermography using thermosensitive thin films as a substrate for the deposition of a fluorophore thin film. The presented thesis work consisted in characterizing, implementing and validating this new electromagnetic field imaging system.; Avec la multiplication des sources rayonnantes dans notre environnement, nous assistons au développement de moyens techniques permettant de tester, mesurer et visualiser le champ électromagnétique. Cette demande des industriels a engendré le développement de différentes technologies d'imagerie du champ et plusieurs approches ont été proposées dont la plupart reposent sur des processus de balayage d’une sonde ponctuelle. Elles seront brièvement présentées dans cette thèse. Il existe également des solutions plus originales utilisant des méthodes optiques pour visualiser le champ.A l'ONERA le choix a été fait de développer une méthode de thermographie infrarouge permettant la caractérisation du champ électrique (EMIR : ElectroMagnetic InfraRed). Des améliorations apportées à cette méthode, et notamment la modulation / démodulation synchrone, ont permis de la rendre quantitative. Plus récemment cette technique a été adaptée à la visualisation du champ magnétique. Cependant les caméras infrarouges hautes performances sont d'un coût très élevé (plusieurs dizaines de milliers d'euros). L'idée d'une thermographie dans le visible, avec une simple caméra sCMOS, a donc vu le jour : passer du domaine de l'infrarouge au domaine du visible permet en effet une économie substantielle sur le coût caméra, à résolution et dynamique équivalentes par ailleurs, voire supérieures. Mais la transition entre l'infrarouge et le visible nécessite de rendre « visible » un échauffement. Un moyen de faire cette transition est d'exploiter les propriétés thermofluorescentes de certains fluorophores, dont la fluorescence dépend précisément de la température. Pour cela nous nous basons sur les travaux préalablement réalisés sur la thermographie infrarouge, en utilisant les films minces thermosensibles comme substrat pour le dépôt d’une fine couche de fluorophore. Les travaux de thèse présentés ont consisté à caractériser, mettre en œuvre et valider ce nouveau système d’imagerie des champs électromagnétiques hyperfréquences.

Current and future wireless communications systems have to be smart while proposing an acceptable quality of service for given applications and optimized resource management in terms of energy consumption and spectral occupation. Moreover, the demand for nomadic devices is growing, thus requiring light, low profile and miniaturized microwave components which can easily integrate into complex systems. All these requirements can be contradictory for the conventional microwave engineer since for instance, miniaturization is usually achieved with a non-negligible impact on overall performances. Since metamaterials can be tailored to present required electromagnetic properties, it should definitely provide for a higher degree of freedom in the design of both radiative and non-radiative components for wireless systems. The potential of metamaterial to improve the performances of microwave devices should also be considered. This chapter is divided in two main parts: the first one deals with metamaterial applications for non-radiative microwave components and the second one describes the potential and applications of metamaterials to microwave antennas.

Microwave hyperthermia appears as an adjuvant technique to heat relatively small tumors in a minimally invasive way. As this technique is based on interstitial antennas, we propose a review of the physical phenomena involved in the radiation of such antennas in a dispersive medium, using the different analytical modeling developed since the 1970\'s. These modeling have been implemented in a freely available software tool, that will allow antenna designers and medical researchers to perform rapid parameter studies to further understand the role of the several parameters involved; this tool will also help the interpretation of results issued from numerical simulations. Simulation results associated with different antenna geometries are presented and compared to results obtained by several authors.

The in-phase radiation from a conformal metamaterial surface is numerically and experimentally reported. The LC-resonant metasurface is composed of a simultaneously capacitive and an inductive grid constituted by copper strips printed on both sides of a dielectric board. The metasurface is designed to fit a curved surface by modifying its local phase. The latter phase-compensated metasurface is used as a reflector in a conformal Fabry-Pérot resonant cavity designed to operate at microwave frequencies. Far-field measurements performed on a fabricated prototype allow showing the good performances of such a phase-compensated metasurface in restoring in-phase emissions from the conformal surface and producing a directive emission in the desired direction.