Recent advances in engineered gradient metasurfaces have enabled unprecedented opportunities for light manipulation using optically thin sheets, such as anomalous refraction, reflection, or focusing of an incident beam. Here we introduce a concept of multi-channel functional metasurfaces, which are able to control incoming and outgoing waves in a number of propagation directions simultaneously. In particular, we reveal a possibility to engineer multi-channel reflectors. Under the assumption of reciprocity and energy conservation, we find that there exist three basic functionalities of such reflectors: Specular, anomalous, and retro reflections. Multi-channel response of a general flat reflector can be described by a combination of these functionalities. To demonstrate the potential of the introduced concept, we design and experimentally test three different multi-channel reflectors: Three-and five-channel retro-reflectors and a three-channel power splitter. Furthermore, by extending the concept to reflectors supporting higher-order Floquet harmonics, we forecast the emergence of other multiple-channel flat devices, such as isolating mirrors, complex splitters, and multi-functional gratings.arXiv:1610.04780v2 [physics.optics]
Control of electromagnetic waves using engineered materials is very important
in a wide range of applications, therefore there is always a continuous need
for new and more efficient solutions. Known natural and artificial materials
and surfaces provide a particular functionality in the frequency range they
operate but cast a "shadow" and produce reflections at other frequencies. Here,
we introduce a concept of multifunctional engineered materials that possess
different predetermined functionalities at different frequencies. Such response
can be accomplished by cascading metasurfaces (thin composite layers) that are
designed to perform a single operation at the desired frequency and are
transparent elsewhere. Previously, out-of-band transparent metasurfaces for
control over reflection and absorption were proposed. In this paper, to
complete the full set of functionalities for wave control, we synthesize
transmitarrays that tailor transmission in a desired way, being "invisible"
beyond the operational band. The designed transmitarrays for wavefront shaping
and anomalous refraction are tested numerically and experimentally. To
demonstrate our concept of multifunctional engineered materials, we have
designed a cascade of three metasurfaces that performs three different
functions for waves at different frequencies. Remarkably, applied to volumetric
metamaterials, our concept can enable a single composite possessing desired
multifunctional response.Comment: 9 pages, 9 figures, journal pape
A new antenna system concept is presented where a wide-scan focal plane array antenna is used to achieve point-to-multipoint communication. The focal plane of a parabolic toroid reflector is populated with several antenna arrays, the positions of which determine the directions of the beams. This concept is investigated for beams pointed towards 0 • (broadside) and 28 • in azimuth. Each array allows for scanning an additional ±1 • in azimuth and elevation. This allows for compensation of twist and sway of the antenna mast. Several array configurations are compared in terms of directivity and scan loss for such a system at E-band. It is found that an 8-by-8 array with an inter-element spacing of 0.7λ0 results in an optimal directivity with a scan loss lower than 1dB when scanning ±1 • in azimuth and elevation. For the 0 • beam direction the directivity is 45.5dBi and for the 28 • beam direction the directivity is 44.4dBi, showing the wide angle scanning properties of this system. An experimental system is built at K-band and measurements are performed showing this system in action. In the measurements an array of 8-by-8 is used with an inter-element spacing of 0.5λ0. The scan loss when scanning ±2 • in azimuth and elevation is below 1dB. The directivity is 37.0dBi and 35.4dBi for the 0 • and 28 • beam directions, respectively. The spillover losses and aperture efficiencies are also found, as well as a relative metric for the transmitted power and the effective isotropic radiated power for both the E-band and K-band systems.
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This article introduces the FORMAT array, a reconfigurable millimeter-wave antenna array platform based on antenna tiles. FORMAT stands for Flexible Organization and Reconfiguration of Millimeter-wave Antenna Tiles, which is a unique hardware solution aiming to implement and demonstrate a variety of antenna array concepts, as well as different array architectures and configurations from the same basic module, providing even benchmark between different solutions and thus valuable insights into 5G and beyond-5G antenna systems. The combination of a minimum-sized 2×2 tile with 3D-printed frame parts enables antenna arrays of a variety of sizes, allows multiple beamforming architectures and a range of different antenna element positioning in the array. The hardware implementation is thoroughly described, with a few different array assemblies being manufactured and measured, validating their antenna performance with over-the-air measurements. Finally, using FORMAT hardware as both base station and user equipment, a 5 meter wireless communication link was set up, achieving 4.8 Gbps downlink speed with QAM64 modulation.
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