Technological Process to Control the Foam Dielectric Constant Application to Microwave Components and Antennas

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 (Polyvinyl chloride, resin, and...) into which gas is injected. Therefore, the dielectric constant of such foam is close to one. 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). Because of 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. The 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.