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The desire to counter multipath effects and improve communication links between mobile wireless systems in dense environment has led to much research in implementing antenna diversity. Space diversity, utilizing two or more antennas separated several wavelengths from one another, is one of the most popular method to achieve this operation. Meanwhile, polarization diversity, utilizing two orthogonal polarizations, has become more attractive in reducing cost and size of antenna systems. Polarization diversity is achieved using two orthogonal feeds to excite the two orthogonal polarization planes of the antenna. The challenge associated with designing dual polarized antennas is the need to reduce isolation between the feed and cross polarization level while maintaining a high efficiency. While a number of studies are successful in realizing polarization diversity, their antenna structure typically present more complex structures involving multiple layers. This thesis presents a novel method to implement polarization diversity on a miniature antenna using a simple planar structure. The antenna structure uses two crossed slots further miniaturized using a method derived from a recent study on miniaturized spiral slot antenna. At an operating frequency of ~ 1 GHz, the antenna is capable of achieving efficiency greater than 90% with a size as small as 0.08 .? x 0.08? The dual polarization operation is achieved by exciting the magnetic currents of the crossed slots with two orthogonal coplanar waveguide feeds. Simulation results of the proposed antenna yield an isolation > 15 dB with cross polarization levels > 10 dB. Theantenna structure was designed using CST Microwave Studio and the simulations were performed using IE3D simulation software.

Les objectifs de ce travail concernent l'étude, la conception et la caractérisation d'antennes miniatures actives ou passives, large bande ou bande étroite fonctionnant en bandes MF, HF et VHF. Le manuscrit est divisé en cinq parties : La première partie présente un système de caractérisation d'antennes qui a été développé, validé et utilisé pour tous les aériens conçus. Ce système, basé sur une cellule à plaque parallèles (PPC), permet un large spectre de mesures telles que la mesure du gain, du point de compression, de l'intermodulation et de la sensibilité via une méthode rayonnée, particulièrement intéressante dans le cas des antennes actives intégrées. La deuxième partie concerne les antennes solénoïdales sur ferrite. L'utilisation de simulateurs électromagnétiques 3D a permis d'obtenir des résultats qui sont comparés à la théorie proposée dans la littérature. Les principaux systèmes d'adaptation d'impédance sont également étudiés. La troisième partie met en avant la possibilité de concevoir des antennes à substrat ferromagnétique de géométrie non conventionnelle en utilisant des matériaux composites. Deux antennes miniatures fabriquées et fonctionnant en bande VHF permettent d'illustrer ce point. Dans la quatrième partie, nous présentons un concept d'antennes à substrat ferromagnétique partiellement saturé. L'utilisation d'une source de champ magnétique statique associée à un matériau initialement dispersif permet de constater un certain nombre de phénomènes intéressants, tels que l'amélioration de l'efficacité tout en préservant l'adaptation de l'antenne ou bien la création de directivité sur des antennes électriquement très compactes. La dernière partie présente la valorisation du travail à travers un projet de télécommunication hertzienne longue portée s'inscrivant dans le cadre de la navigation maritime. / The objectives of this work concern the study, the design and the measurement of miniaturized passive and active, broadband and narrowband antennas for MF, HF and VHF frequency bands. The thesis is divided into five parts : The first part deals with a measurement system, which has been developed, validated and used for all conceived aerials. The system is based on a parallel plate cell (PPC) and allows an evaluation of the gain, the compression point, the interception point and the sensitivity using a radiative method particularly useful in the case of active integrated antennas. The second part concerns solenoidal ferrite antennas. The results obtained from electromagnetic 3D simulators were compared to the state of the art theory. Main matching technics have also been studied. The third part put the light on the possibility of development of arbitrary shaped antennas on a ferromagnetic substrate using a composite material. Two antennas developed for the VHF band, confirm this point. In the fourth part, we present a concept of antennas on a partially saturated ferromagnetic substrate. A static magnetic field associated with an initially lossy material brings up some interesting phenomena such as an increased efficiency without a degradation of the impedance matching or the directivity with very small antennas. The last part presents an application of the work across a project dedicated to long distance telecommunications in marine navigation.