Universal behaviour of a wave chaos based electromagnetic reverberation chamber

In this article, we present a numerical investigation of three-dimensional electromagnetic Sinai-like cavities. We computed around 600 eigenmodes for two different geometries: a parallelepipedic cavity with one half- sphere on one wall and a parallelepipedic cavity with one half-sphere and two spherical caps on three adjacent walls. We show that the statistical requirements of a well operating reverberation chamber are better satisfied in the more complex geometry without a mechanical mode-stirrer/tuner. This is to the fact that our proposed cavities exhibit spatial and spectral statistical behaviours very close to those predicted by random matrix theory. More specifically, we show that in the range of frequency corresponding to the first few hundred modes, the suppression of non-generic modes (regarding their spatial statistics) can be achieved by reducing drastically the amount of parallel walls. Finally, we compare the influence of losses on the statistical complex response of the field inside a parallelepipedic and a chaotic cavity. We demonstrate that, in a chaotic cavity without any stirring process, the low frequency limit of a well operating reverberation chamber can be significantly reduced under the usual values obtained in mode-stirred reverberation chambers

Statistiques spatiales ces cavités chaotiques ouvertes : Applications aux cavités électromagnétiques

Mode-stirred reverberation chambers (RC) are used in the industry to test the immunity or the susceptibility of on-board electronic systems (plane, automobile, smartphone) towards the electromagnetic waves present in their environment. Mode-stirred RCs have to comply with a number of statistical criteria fixed by international standards. The chief criterion relies on a statistically uniform and isotropic field around the object under test. In order to improve and master the statistical properties of these systems for frequencies close to their lowest useable frequency, we suggest making them chaotic to take advantage of universal statistical properties of the resonances of chaotic cavities. We first show how to make chaotic RCs by simple modifications of a conventional RC and how to extend the predictions of the random matrix theory applied to the effective hamiltonien describing the open chaotic systems, to the case of vectorial fields. Then, we compare, by means of simulations and experiments, the distributions of intensity and the fluctuations of the maxima of the field in a conventional RC and in a chaotic RC close to the lowest useable frequency. This work illustrates that the universal spectral and spatial statistical properties of chaotic RCs allow to better comply with the criteria required by the international standards.Les chambres réverbérantes à brassage de modes (CRBM) utilisées dans l'industrie pour tester l'immunité ou la susceptibilité des systèmes électroniques embarqués (avion, automobile , smartphone,...) vis-à-vis des ondes électromagnétiques (EM) présentes dans leur environnement. Les CRBM doivent toutes répondre à un certain nombre de critères statistiques fixés par une norme internationale. Le critère principale étant l'obtention d'un champ statistiquement uniforme et isotrope autour de l'objet sous test. Afin améliorer et de mieux maitriser les propriétés statistiques de ces systèmes pour des fréquences proches de leur fréquence minimale d'utilisation, nous proposons de les rendre chaotiques afin de profiter des propriétés statistiques universelles des résonances des cavités chaotiques. Nous commencerons par montrer comment rendre chaotique, par des modifications simples, des chambres réverbérantes conventionnelles, et comment étendre les prédictions de la théorie des matrices aléatoire appliquée (TMA) à l'hamiltonien effectif, permettant de décrire les systèmes chaotiques ouverts, au cas de systèmes décrits par des champs vectoriels. Ensuite, nous comparerons, au moyen de simulations et d’expériences, les distributions d'intensité et les fluctuations des maxima du champ EM dans une CRBM conventionnelle et dans une CR chaotique au voisinage de la fréquence minimale d’utilisation. Ce travail illustre que les propriétés statistiques spectrales et spatiales universelles des CR chaotiques permettent de mieux répondre aux critères exigés par la norme internationale pour réaliser des tests de compatibilité électromagnétiques

A Wave Physics Approach to Electronically Steerable Antennas

Electronically steerable antennas, that are compact, thin, light and contain no mechanical parts, are being more and more used for satcom applications on the ground, notably owing to the fast development of mega constellations; yet their use is still very limited on board. Indeed, all designs up to date rely on the same old concept, phased arrays, namely, a large number of sources that are phased matched to point in various directions. These can be passive, in the sense that a common feed is used to radiate through many radiators, or active in which case each tiny emitter contains its own source of waves. While the former are relatively simpler and less energy greedy, they are very dissipative and hence of poor efficiency. The latter, on the contrary, often offer good performances, yet they are extremely costly and require huge amounts of electrical power to operate, the vast majority of which is dissipated into heat. In a nutshell, both active and passive phased arrays have tremendous problems when it comes to space applications. Here we introduce the concept of the reconfigurable leaky cavity antenna, that stems on a radically different approach to beamforming. It uses a thin leaky cavity that, when excited by one or several feeds, can establish any desired wavefield corresponding to any desired radiation pattern. To achieve this, the cavity is reconfigured in real time by an electronically reconfigurable intelligent surface (metasurface). The latter controls the reflections of the waves inside the cavity, acting as a software-controlled set of boundary conditions. Being based on discrete components, the antenna maintains the cost-efficiency, robustness and power sobriety of the simplest passive phased arrays, with a power needed for beamforming as low as a few tens of watts at Ku or Ka. In the meantime, since the control is solely based on electronics, it achieves the performances of active phased arrays at the same time, for instance in terms of gain or switching speeds. With its high performances and low complexity, our concept paves the way to the deployment of electronically steerable antennas on board. Further, since the beamforming does not result from the synchronization of many elementary sources, but rather on the shaping of a wavefield inside a cavity, our concept is standard or protocol agnostic. Moreover, it is able to support multiple frequency bands, and to emit multiple beams, at different frequencies and with different polarization

Universal intensity statistics in a chaotic reverberation chamber to refine the criterion of statistical field uniformity

International audienceThis article presents a study of the intensity statistics of the electromagnetic response in a chaotic reverberation chamber (RC) in the presence of losses. Through an experimental investigation, intensity statistics of the response in a conventional mode-stirred RC are compared with those in a chaotic RC in the neighborhood of the Lowest Useable Frequency. The present work illustrates how the universal statistical properties of the field in an actual chaotic RC can ensure the validity of the standard criterion proposed to evaluate the uniformity of the field distribution. In particular, through a theoretical approach based on the random matrix theory applied to open chaotic systems, we find that the modal overlap seems to be the only relevant parameter of the corresponding intensity distribution

Statistiques de la réponse électromagnétique d'une chambre réverbérante chaotique

Cet article présente une étude de la réponse électromagnétique d'une chambre réverbérante (CR) chaotique en présence de pertes. Au moyen de simulations et d'expériences, sont comparées les fluctuations des maxima du champ obtenus dans une CR à brassage de modes conventionnelle et dans une CR chaotique au voisinage de la fréquence minimum d'utilisation. Ce travail illustre que les propriétés statistiques spectrales et spatiales universelles des CR chaotiques permettent de mieux répondre aux critères exigés par la norme pour réaliser des tests d'immunité ou de compatibilité électromagnétique

Reconfigurable Intelligent Surface-assisted Classification of Modulations using Deep Learning

The fifth generating (5G) of wireless networks will be more adaptive and heterogeneous. Reconfigurable intelligent surface technology enables the 5G to work on multistrand waveforms. However, in such a dynamic network, the identification of specific modulation types is of paramount importance. We present a RIS-assisted digital classification method based on artificial intelligence. We train a convolutional neural network to classify digital modulations. The proposed method operates and learns features directly on the received signal without feature extraction. The features learned by the convolutional neural network are presented and analyzed. Furthermore, the robust features of the received signals at a specific SNR range are studied. The accuracy of the proposed classification method is found to be remarkable, particularly for low levels of SNR

Multi-path fading and interference mitigation with Reconfigurable Intelligent Surfaces

We exploit multi-path fading propagation to improve both the signal-to-interference-plus-noise-ratio and the stability of wireless communications within electromagnetic environments that support rich multipath propagation. Quasi-passive propagation control with multiple binary reconfigurable intelligent surfaces is adopted to control the stationary waves supported by a metallic cavity hosting a software-defined radio link. Results are demonstrated in terms of the error vector magnitude minimization of a quadrature phase-shift modulation scheme under no-line-of-sight conditions. It is found that the magnitude of fluctuation of received symbols is reduced to a stable constellation by increasing the number of individual surfaces, or elements, thus demonstrating channel hardening. By using a second software-defined radio device as a jammer, we demonstrate the ability of the RIS to mitigate the co-channel interference by channel hardening. Results are of particular interest in smart radio environments for mobile network architectures beyond 5G

Comparison of reverberation chamber shapes inspired from chaotic cavities

International audienceUsing the knowledge gained from the wave chaos theory, we present simple shapes of resonant cavities obtained by inserting metallic hemispheres or caps on the walls of a parallelepiped-shaped cavity. The presented simulation results show a significant improvement of the field statistical properties when the number of hemispheres or caps increases, and the comparison with a classical reverberation chamber geometry shows an improved homogeneity and isotropy can be attained using these new proposed shapes