Auswahl der wissenschaftlichen Literatur zum Thema „Active beamsteering“

Recent works have demonstrated the feasibility of microwave imaging using compressive techniques, exempting the use of active delay lines, phase shifters, or moving parts to achieve beamforming. With this method, waves are coded in a passive way by a compressive device to reduce the complexity of the transmitter and/or receiver chains of the telecommunication and radar systems requiring beamsteering. Such a technique is based on the exploitation of the frequency diversity, implying that a reduction of the compressive device's volume imposes a diminution of the number of driven antennas. In this paper, the improvement brought by simultaneous excitations of the compressive device is presented. Adapting a new mathematical formulation, it is shown that M inputs can send independent waveforms allowing the beamsteering of an N-elements antenna array, while maintaining N > M.

An overview about some of the recent Spanish developments on active reflectors is presented. In the first part, a novel beamsteering active reflectarray is deeply studied. It is based on implementing in each elementary radiator an IQ modulator structure, in which amplitude and phase control of the scattered field is achieved. Finally, a special effort is made in offering solutions to overcome the active antenna integration problems. In the second part, the active concept is firstly extended to Fresnel reflectors. Thanks to the development of a proper simulator, this special structure can be easily analysed. This simulator allows the study of performance of this kind of reflectors and, applying evolutionary algorithms, to find optimal configurations of reflector in accordance with the given specifications for the conformal radiation pattern.

In this work, toward an intelligent radio environment for 5G/6G, design methodologies of active split-ring resonators (SRRs) for more efficient dynamic control of metasurfaces are investigated. The relationship between the excitation of circulating-current eigenmode and the asymmetric structure of SRRs is numerically analyzed, and it is clarified that the excitation of the circulating-current mode is difficult when the level of asymmetry of the current path is decreased by the addition of large capacitance such as from semiconductor-based devices. To avoid change in the asymmetry, we incorporated an additional gap (slit) in the SRRs, which enabled us to excite the circulating-current mode even when a large capacitance was implemented. Prototype devices were fabricated according to this design methodology, and by the control of the intensity/phase distribution, the variable focal-length and beamsteering capabilities of the transmitted waves were demonstrated, indicating the high effectiveness of the design. The presented design methodology can be applied not only to the demonstrated case of discrete varactors, but also to various other active metamaterials, such as semiconductor-integrated types for operating in the millimeter and submillimeter frequency bands as potential candidates for future 6G systems.

AbstractNonreciprocal radiation refers to electromagnetic wave radiation in which a structure provides different responses under the change of the direction of the incident field. Modern wireless telecommunication systems demand versatile apparatuses which are capable of full-duplex nonreciprocal wave processing and amplification, especially in the reflective state. To realize such a functionality, we propose an architecture in which a chain of series cascaded radiating patches are integrated with nonreciprocal phase shifters, providing an original and efficient apparatus for full-duplex reflective beamsteering. Such an ultrathin reflective metasurface can provide directive and diverse radiation beams, large wave amplification, steerable beams by simply changing the bias of the gradient active nonmagnetic nonreciprocal phase shifters, and is immune to undesired time harmonics. Having accomplished all these functionalities in the reflective state, the metasurface represents a conspicuous apparatus for efficient, controllable and programmable wave engineering.

Abstract The ever increasing number of wireless devices and systems has led to a crowded spectrum and increased the demand for versatile and multi-functional wireless apparatuses. Recently, metasurfaces are explored as a prominent technological solution to the current paradigm of spectrum scarcity by opportunistically sharing the spectrum with various users. In general, metasurfaces are passive/dynamic, ultra-compact, multi-functional and programmable structures which are capable of both reciprocal and nonreciprocal signal wave transmissions. The controllability and programmability of such metasurfaces are governed through DC bias and occasionally a radio-frequency (RF) modulation applied to the active components of the unit cells of the metasurface, e.g., diodes and transistors. This article overviews some of the recently proposed passive and dynamic metasurfaces and shows that metasurfaces can enhance the performance of wireless communications systems thanks to their unique physical features such as real-time signal coding, nonreciprocal-beam radiation, nonreciprocal beamsteering amplification, and advanced pattern-coding multiple access communication.

Dans le domaine des télécommunications de nouvelle génération, le développement rapide des protocoles de communication en bande millimétrique et la diversification des réseaux terrestres et non terrestres, tels que les constellations de satellites en orbite basse (LEO), sont remarquables. La transition vers ces bandes de fréquences élevées est essentielle en raison de la saturation des bandes plus basses. Cependant, les signaux à ces fréquences subissent des pertes importantes dues à la propagation et à l'absorption atmosphérique, augmentant ainsi les coûts des systèmes antennaires nécessaires pour compenser ces pertes. Un système de balayage électronique du faisceau est également requis pour réduire les interférences, en focalisant les faisceaux sur chaque utilisateur. Dans ce contexte, les antennes de type réseau transmetteur (Transmit-Array, TA) émergent comme une solution prometteuse. Contrairement aux réseaux phasés traditionnels, elles ne nécessitent pas de réseau de formation de faisceau, réduisant ainsi les pertes, la complexité de conception et les coûts. Ces antennes, également appelées "lentilles discrètes", se composent de cellules unitaires périodiquement disposées qui déphasent localement le champ incident pour former et balayer le faisceau mécaniquement ou bien électroniquement.Cette thèse se concentre sur le développement des TAs à faisceaux reconfigurables pour les télécommunications en bande millimétrique. En intégrant des composants actifs tels que les diodes PIN, nous démontrons la capacité du réseau à contrôler électroniquement le gradient de phase sur son ouverture, permettant ainsi la formation et le balayage 2D variable du faisceau sur une large angle d’ouverture. Par ailleurs, cette thèse vise à concevoir des cellules unitaires reconfigurables qui assurent également une conversion de polarisation linéaire vers circulaire (PL-PC) avec une large bande passante et un faible taux d’ellipticité.Dans un premier temps, nous avons proposé et validé expérimentalement deux réseaux passifs en bande X et Ka, en introduisant un concept de cellule unitaire qui réalise une conversion PL-PC à large bande et avec de faibles pertes d’insertion. Cette cellule a démontré une transmission très efficace et des performances supérieures à l'état de l'art en termes de bande passante, de gain et de taux d’ellipticité. Nous avons réalisé deux TAs : un premier en bande X comportant 20×20 cellules et un deuxième en bande Ka composé de 70×70 cellules à très fort gain et très bonne efficacité d’ouverture.Suite aux performances prometteuses du concept passif, nous avons développé une configuration active dite reconfigurable. En intégrant une paire de diodes PIN, nous avons réalisé une commutation de phase 1-bit contrôlable électroniquement. L’étude a porté sur l'implantation des composants actifs, leur modélisation, l'intégration du réseau de polarisation des diodes à la cellule unitaire, et leur contrôle pour générer une loi de phase imposée par un cahier des charges. La cellule a été développée en bande X pour valider le concept, puis en bande Ka pour démontrer la faisabilité et les performances du concept en bande millimétrique pour les applications de cinquième génération (5G). Un réseau 14×14 cellules a été fabriqué en bande X (validation du concept), tandis qu’en bande Ka un réseau 20×20 cellules a été réalisé, centré à 27.5 GHz.Nous avons mis au point un système électronique utilisant un microcontrôleur et des cartes de multiplexage pour le contrôle dynamique de la polarisation des diodes lors des mesures. Nous avons prouvé la possibilité de réaliser un balayage électronique 2D entre ±60°, avec des taux d’ellipticité inférieurs à 2 dB. Ce concept s’avère prometteur pour des applications de type SatCom, avec un potentiel pour les stations au sol communiquant avec les constellations de satellites en orbite LEO, ainsi que pour des applications radar et le « backhauling » dans les réseaux hétérogènes 5G
In the field of next-generation telecommunications, the rapid development of millimeter-wave communication protocols and the diversification of terrestrial and non-terrestrial networks, such as low Earth orbit (LEO) satellite constellations are remarkable. The transition to these high-frequency bands is essential due to the saturation of lower frequency bands. However, signals at these frequencies experience significant losses due to propagation and atmospheric absorption, thereby increasing the costs of antenna systems needed to compensate for these losses. A beam scanning system is also required to reduce interference by focusing the beams on each user and minimizing radiation toward neighboring links.In this context, Transmit-Array (TA) antennas emerge as a promising solution. Unlike traditional phased arrays, they do not require a beam-forming network, thus reducing losses, design complexity, and costs. These antennas, also known as "discrete lenses," consist of unit cells periodically arranged that locally phase-shift the incident field to form and scan the beam mechanically or electronicallyThis thesis focuses on the development of reconfigurable beam Transmit-Array antennas for millimeter-wave telecommunications. By integrating active components such as PIN diodes, we demonstrate the network's ability to control electronically the phase gradient across its aperture, thereby enabling variable beam formation and scanning over a wide-angle range. Additionally, this thesis aims to design reconfigurable unit cells that also achieve linear-to-circular polarization (LP-CP) conversion with wide bandwidth and low ellipticity.Initially, we proposed and experimentally validated two passive networks in the X and Ka bands by introducing a unit cell concept that achieves wideband LP-CP conversion with low insertion loss. This cell demonstrated highly efficient transmission and superior performance in terms of bandwidth, gain, and ellipticity compared to the state of the art. We developed two Transmit-Array prototypes: the first one in the X band with 20×20 cells, whereas, the second one in the Ka band with 70×70 cells, featuring high gain and aperture efficiency.Following the promising performances of the passive concept, we developed an active or reconfigurable configuration. By integrating a pair of PIN diodes on each unit cell, we achieved electronically controllable 1-bit phase switching. The study focused on the implementation of components, their modeling, and the integration of the diode biasing network into the unit cell and their real time control. The cell was developed in the X band to validate the concept, and then in the Ka band to demonstrate the feasibility and performance of the concept in the millimeter-wave band for fifth-generation (5G) applications. A 14×14 cell array was fabricated in the X band, while a 20×20 cell array was realized in the Ka band, centered at 27.5 GHz.We developed an electronic system using a microcontroller and multiplexing boards for the dynamic control of diode polarization during measurements. We demonstrated the capability to achieve 2D electronic beam scanning between ±60°, with ellipticity levels below 2 dB. This concept proves promising for SatCom applications, with potential for ground stations communicating with LEO satellite constellations, as well as for radar applications and backhauling in heterogeneous 5G networks

In this work, we summarize our recent advances in 2D beamsteering using optical phased arrays operating in NIR and SWIR wavelengths, covering different architectures and steering techniques based on active phase shifting and wavelength tuning.