Fraunhofer Institute for High Frequency Physics and Radar Techniques FHRThe field‑of‑view range of phased array antennas is inherently limited by physical constraints. Through the use of electronically tunable metamaterials, this range could be expanded in the long term, thereby enabling new application possibilities
Product developers seek to maximize the number of degrees of freedom available in design and development. Metamaterials have the potential to expand these degrees of freedom in the future: unlike conventional materials, their properties and frequency characteristics can be defined directly by the developers themselves—including values that do not occur in nature. This enables materials to be tailored precisely to specific requirements. For example, it is possible to fabricate materials in which waves cannot propagate within certain frequency ranges. Metamaterials consist of cells that can be manufactured using technologies such as printed circuit board processes or 3D printing, and whose dimensions are significantly smaller than the wavelength.
Metamaterials also introduce an additional degree of freedom in antenna development: they can be used to realize specific shielding or wave‑attenuation characteristics. This opens up concrete advantages for the development of high‑performance radar systems. The question arises: how can military radar systems be improved through metamaterials? This was investigated by Fraunhofer FHR in collaboration with the Spanish company Tafco Metawireless S.L. and the Public University of Navarra within the project METALESA II, funded by the European Defence Agency.
Fraunhofer FHR focused on array antennas composed of numerous smaller antenna elements and featuring a curved radiating surface. Typically, the viewing angle of such antennas is adjusted electronically, but the electronic steering range has so far been very limited.
Expanded scan range through intelligent material control
Within METALESA II—short for Metamaterials for Active Electronically Scanned Array—researchers at Fraunhofer FHR worked to expand the scan range and enhance the performance of curved antennas using tunable metamaterials. The underlying principle is that the scan direction of an antenna array depends on the relative phase of the wavefronts emitted by the individual antenna elements. By employing electronically tunable metamaterials, the researchers aim to further modify the phases of the emitted wavefronts and thereby extend the steering range. The phase‑modifying properties of these specialized metamaterials can be adjusted via DC voltage applied to the capacitances of integrated varactor diodes.
Prototypes demonstrate tangible benefits
But to what extent can such tunable metamaterials influence the phase of radar radiation? And what losses occur in the process? The researchers examined these questions using various test setups and prototypes. They fabricated and characterized two large metamaterial circuit boards measuring 24 by 16 centimeters. In an initial experiment, the tunable metamaterial plates were mounted in front of a transmitting antenna, and the radiation pattern was analyzed using a receiving antenna. The results were highly promising: for both horizontal and vertical polarization, phase shifts of up to 170° were achieved. Losses were low, in the range of 1 to 2 dB.
In the next step, the researchers designed and built two prototypes. The first consisted of a single tunable metamaterial plate, while the second featured a faceted arrangement of multiple metamaterial plates positioned in front of a curved antenna array.
Performance enhancement in a compact design
In the first prototype, functionalities such as phase compensation for beam focusing and beam collimation (similar to a lens), as well as beam steering, were successfully demonstrated. For both polarizations, a scan range of ±60° was achieved, accompanied by an increase in antenna gain of 3 dB, all within a highly compact structure featuring a metasurface thickness of only one millimeter.
The prototype combining the curved antenna array with the faceted metamaterial layer also proved effective: within an azimuthal scan range of 70° to 90°, the use of tunable metamaterial plates resulted in an improvement in antenna gain of 1 to 2 dB for horizontal polarization.
These results are particularly relevant for small platforms such as drones, which are too small to carry large antenna arrays. The new technology will make it possible to use a lightweight, cost‑efficient system with only a single antenna while still achieving high gain and enabling electronic adjustment of the antenna’s viewing direction.
Currently, researchers at Fraunhofer FHR are working within the follow‑up project E‑DOME to further explore the limits of the existing metasurface and, based on the insights gained, to develop an even more advanced metasurface.
