Several smooth-walled axis-symmetrical dielectricloaded horn antennas with large flare angles have been designed and characterized in Ka-band. They have been optimised using an in-house CAD tool based on the BoR-FDTD technique and genetic algorithms. Two antenna configurations have been compared: in the first case, only the metallic profile of the horn is shaped and the radiating aperture remains flat, whereas in the second one, the shapes of the horn profile and the aperture are simultaneously optimized. The impact of both techniques in terms of antenna size and performance is discussed. An original fabrication process (metallized foam) has been developed to produce monolithic prototypes. Two prototypes with optimized shapes have been fabricated, and their main characteristics (radiation characteristics, bandwidth, compactness, weight) are compared to those of a standard conical horn used as a reference (same flare angle, same diameter, but without shaped profile). Our results show that the proposed design and fabrication procedures enable us to produce reduced-size horns with high radiation efficiency; the total loss, including the transition loss, is lower than 1dB in average around 29.5 GHz.

A new design method for multi-access antennas is presented. This method is based on a modal analysis assuming the microstrip antennas as a resonant cavity. Using this cavity approach, the eigenmodes perturbation induced by the cavity deformation (adding slots or short circuits) is studied. As an application, a solution of multi-access antenna with two ports, with operating frequency bands centered approximately on digital cellular system (DCS) and universal mobile telecommunication system (UMTS)/Wi-Fi standards is developed. These two ports are isolated using the previous original design method. In addition to the design method, the innovation of the structure resides on its application in terms of flexibility, reconfigurability, and portability for the future development of a unique system that allows cross services where telephony joined multimedia and online services. The design method and the performances are validated through comparisons between simulations and measurements.

Electromagnetic scattering by penetrable bodies often is modelled by the Poggio-Miller-Chan-Harrington-Wu-Tsai (PMCHWT) integral equation. Unfortunately the spectrum of the operator involved in this equation is bounded neither from above or below. This implies that the equation suffers from dense discretization breakdown; that is, the condition numbers of the matrix resulting upon discretizing the equation rise with the mesh density. The electric field integral equation, often used to model scattering by perfect electrically conducting bodies, is susceptible to a similar breakdown phenomenon. Recently, this breakdown was cured by leveraging the Calderón identities. In this paper, a Calderón preconditioned PMCHWT integral equation is introduced. By constructing a Calderón identity for the PMCHWT operator, it is shown that the new equation does not suffer from dense discretization breakdown. A consistent discretization scheme involving both Rao-Wilton-Glisson and Buffa-Christiansen functions is introduced. This scheme amounts to the application of a multiplicative matrix preconditioner to the classical PMCHWT system, and therefore is compatible with existing boundary element codes and acceleration schemes. The efficiency and accuracy of the algorithm are corroborated by numerical examples.

Nous discutons, à partir d'une étude de cas, GeoRezo, l'implication des participants à des collectifs ou projets qui produisent de la connaissance ou des biens (type logiciels) ou des services en ligne. Cette « carrière » est vue sous deux angles : les facteurs favorisant des prises de rôles ; les raisons de l'engagement.