Extended scanning range for array antennas
The scanning range of array antennas is physically limited. It could be extended in the long term by electronically tunable metamaterials.
Product developers want as much freedom as possible in development and design. In contrast to conventional materials, the properties and frequency characteristics of metamaterials can be adjusted by the developers themselves – even values that do not occur in nature are possible. For example, materials can be manufactured in which waves cannot propagate in certain frequency ranges. This is because metamaterials consist of periodic subwavelength unit cells that are produced using printed circuit board technology or 3D printing.
Metamaterials provide a further degree of freedom in the development of antennas, among other things: They can be used, for example, to realize specific shielding properties or wave absorption characteristics. But how can military radar systems be improved using metamaterials? Fraunhofer FHR is investigating this together with the Spanish company Tafco Metawireless S.L. and the Universidad Pública de Navarra, also in Spain, in the METALESA II project for the European Defence Agency. Fraunhofer FHR is focusing on array antennas, which consist of a set of antenna elements and whose radiating surface is curved. Usually, the beam direction of such antennas is adjusted electronically, but the beam scanning range is very limited. Using electronically tunable metamaterials, it is hoped, it may be possible to extend this scanning range. The electromagnetic properties of these special metamaterial structures can be locally adjusted by applying DC voltages to the varactor diodes integrated into the metamaterial unit cells. While the research team in the previous METAFORE project had already conducted an extensive literature research and made technology predictions, as well as introducing one-dimensional transmission line metamaterials and metamaterials designed to suppress parasitic surface waves of specific wavelengths on array antenna apertures in METALESA I, it is now working with electronically tunable metamaterials. The researchers have already successfully measured smaller circuit boards from Fraunhofer FHR to characterize tunable metasurface structures in a test setup, and now larger boards are to follow.
In further steps, the Fraunhofer FHR research team will address the challenges that currently still exist when combining antennas and metamaterials. For example, the bandwidth of antennas should be as large as possible – but the resonance effect of the metamaterials has so far stood in the way of this. In addition, the antenna still loses too much of its gain when the signal penetrates the metamaterials.