There is an increasing interest in using new composite materials in microwave devices, to reduce size and weight while maintaining similar performances. A new promising material group is named magneto-dielectric materials, which have the permittivity and permeability values both larger than one. Compared to the commercially used dielectric materials, magneto-dielectric materials can achieve a larger miniaturization factor with the equivalent properties as dielectric materials. There is a very limited availability of commercial magneto-dielectric materials. A recent addition was from Rogers Corporation with MAGTREX 555, [1], that is available as a printed circuit board laminate. The material is limited to 500 MHz operational frequency due to its increased magnetic and dielectric losses. In this thesis the purpose is to understand the loss mechanisms, characterize and understand the state-of-the-art magneto-dielectric materials at microwaves, and to produce a magneto-dielectric material in the lab to understand the material better. A new material was developed with magneto-dielectric properties. The material was based on a polymer base of polystyrene that serves as a dielectric material and doped with nickel nanoparticles that produce the magnetic properties. The contents of the nanoparticles in the mix is a design variable. Nickel-polystyrene samples with different nickel contents of 0%, 2.3% and 4.5%, were produced in the lab and measured in-house to understand the loss mechanism and RF performance.

Les avions comportent plusieurs systèmes de navigation et de communication nécessitent des antennes VHF large bande. Réduire la taille de ses antennes est un enjeu majeur tout en gardant des bonnes performances. Cette thèse propose des nouvelles configurations d'antennes à profil bas utilisant des nouveaux matériaux nanocomposites non conducteurs constitués de nanoparticules magnétiques développés au Lab-STICC. Un monopole planaire large bande a été développé et optimisé avec un taux de miniaturisation de 60% grâce à l'utilisation d'un matériau magnéto-diélectrique de forte perméabilité et faible pertes couvrant seulement 5% de sa surface. Les résultats expérimentaux, en presque parfait accord avec les simulations, montrent que le diagramme de rayonnement est omnidirectionnel et que la polarisation est verticale, avec un bon niveau du gain. L'antenne monopole planaire insérée dans un MMD des dimensions limitées avec des pertes a été modélisée par un nouveau circuit équivalent multi résonant. Ce circuit est développé à partir de l'impédance d'entrée de l'antenne et des caractéristiques du MMD, et validé par les simulations avec un parfait accord entre les résultats. / Airplanes with multiple navigation and communication systems require broadband VHF antennas. Reduce the size of these antennas is a major challenge while keeping good performances. This thesis proposes new configurations of low profile antennas using new nanocomposite non-conductive materials consisting of magnetic nanoparticles developed at Lab-STICC. A broadband planar monopole has been developed and optimized with a 60% miniaturization rate thanks to the use of a high permeability and low loss magneto-dielectric material covering only 5% of its surface. The experimental results, in almost perfect agreement with the simulations, show that the radiation pattern is omnidirectional and that the polarization is vertical, with a good level of gain. The planar monopole antenna inserted in a MMD of limited dimensions with losses was modeled by a new multi-resonant equivalent circuit. This circuit is developed from the input impedance of the antenna and the characteristics of the MMD. and validated by the simulations with a perfect agreement between the results.