Abstract-A technological process to control the foam dielectric constant, an important issue for the design of microwave components and antennas, is described. For that purpose, the use of different commercial foam materials has been considered. This kind of foam substrate is made of original material (PVC, resin, …) into which gas is injected. So the dielectric constant of such foam is close to 1. It can be increased by expelling the gas out of the foam material. The authors are presenting the technological process used to expel the gas by pressing a foam slab at relatively low temperature (90°C). Thanks to this technological process, the dielectric constant variation can be controlled by the ratio between the initial and final slab thickness. It holds a great interest for the design of microwave antennas and circuits. Indeed, the dielectric constant inside gradient index lenses (Luneburg, Maxwell fish-eye and Fresnel lenses) must follow a particular law to obtain the desired radiation capabilities. Results of materials characterization are presented to validate the technological process. Foam based antennas and components are also shown to illustrate the interest of the process.Index Terms-Foam material, controlled dielectric constant.

International audienceThe conception and performances of a 60 GHz active antenna, reconfigurable in terms of radiation pattern is described in this paper. This antenna is based on a plate inhomogeneous Luneburg lens fed by several ridged waveguide sources. The manufacturing technique of the plate lens is briefly described and its measured radiation patterns are given, showing the good performances of this lens. Simulated and measured radiation patterns are given for a passive lens antenna fed by several sources. The results show the beam scanning capability of this antenna. The active antenna is described and measurements of radiation patterns for several beams are given and demonstrate the beam scanning and beam shaping reconfigurability

Abstract-An innovative technological process is investigated to easily manufacture inhomogeneous Luneburg lenses. A unique foam material is drilled and pressed to achieve the different dielectric constant needed to follow the index law inside the lens. The performance of such 60 GHz antenna is described and the antenna prototype is measured in terms of gain and radiation patterns. The results show a good efficiency (60% with a directivity of and demonstrate the feasibility of this kind of Luneburg lens, through the use of a simple technological process. The lens with a diameter of 56mm and a thickness of 3mm operates in the 57-66 GHz bandwidth. The magnitude of S11 parameter is under -10dB in the whole bandwidth and an half-power beamwidth of 5° and 50° in H-plane and E-plane respectively is reached.

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