Nurad Develops Composite Dual-Reflector Antenna

Nurad Technologies (Baltimore, Md., U.S.A.), a division of Chelton Microwave (Bolton, Mass., U.S.A.), has been manufacturing antennas and composite radomes for more than 35 years. Recently, the company developed a composite dual-reflector antenna system for broadband direction finding and electronic intelligence applications.

The reflector system simultaneously receives and focuses two electromagnetic signals at two different frequency bands. Radomes, which cover and protect antennas, are typically constructed with high-performance fiber composite materials for superior transmissivity characteristics - that is, low loss as the signal passes through the composite material. But the dual-reflector antenna requires a high-quality surface finish for maximum reflectivity, which can be achieved with less costly fiberglass, when it is appropriately metallized.

In the past, Nurad manufactured this contoured part in multiple sections that were subsequently bonded together. For the new one-piece design, a multi-part, separable composite mold was designed and constructed by Nurad Engineering. S-2 glass/epoxy prepreg supplied by Newport Adhesives and Composites Inc. (Irvine, Calif., U.S.A., select 215) is hand layed up in the mold, to form the outer skin. Next, film adhesive from Cytec Engineered Materials Inc. (Tempe, Ariz., U.S.A., select 216) and aramid honeycomb core supplied by Plascore Inc. (Zeeland, Mich., U.S.A., select 217) are layed in the mold. Nurad uses proprietary core forming techniques, which enable the core to conform to the tight mold radii without fracturing. The inner S-2/epoxy skin is then bonded to the core with another ply of film adhesive. Pre-molded fiberglass fittings are integrally molded into the part for mounting the secondary reflector to the primary reflector and the base flange to a rotator. The part is then autoclave cured. After cool down, the separable mold is disassembled and removed piece by piece to demold the part. The reflector surfaces are finished with a sprayed-on coating of conductive copper paint.