Self-Polarizing Fabry-Perot Antennas Based on Polarization Twisting Element

International audienceA new configuration of a self-polarizing Fabry-Perot (FP) antenna is presented to generate circular polarization with high gain levels using a simple linearly polarized feed. It consists of an FP resonator combined with a polarization-twisting ground plane. An analytical model is proposed to facilitate the antenna design, and the corresponding results are shown to be in very close agreement with full-wave simulations. The experimental prototype built in -band exhibits a combined bandwidth (3 dB axial ratio, 3 dB gain drop, and 10 dB impedance matching) of 3% with a maximum realized gain of 18.0 dB. The antenna is completely shielded with an aperture size of and a height of only . Such antennas are attractive candidates for high-power space applications at low frequencies ( -to -bands) where standard horns are very bulky

Atomic fountains and optical clocks at SYRTE: status and perspectives

In this article, we report on the work done with the LNE-SYRTE atomic clock ensemble during the last 10 years. We cover progress made in atomic fountains and in their application to timekeeping. We also cover the development of optical lattice clocks based on strontium and on mercury. We report on tests of fundamental physical laws made with these highly accurate atomic clocks. We also report on work relevant to a future possible redefinition of the SI second

On the Near-Field Shaping and Focusing Capability of a Radial Line Slot Array

International audienceWe describe the design of a radial line slot array antenna with a shaped and focused near field. The antenna is designed in such a way to control the side lobe level and beamwidth of the normal component of the electric field with respect to the radiating aperture. The design procedure consists of two steps. In the first step, the requirements on the near-field pattern are provided over a focusing plane at a given distance from the radiating aperture. A set theoretic approach is then used to derive the aperture field distribution fitting the requirements over the near field. In the second step, the aperture field distribution is synthesized by accurately placing and sizing the slots of the antenna. The spillover efficiency is maximized during the design process. The antenna is centrally fed by a simple coaxial probe. The antenna design is validated by a prototype and measurements at 12.5 GHz

"Phoenix' reflectarray unit cell with reduced size and inductive loading

This study presents a new Phoenix unit cell with reduced size (l0/3 at centre frequency). Three different techniques are investigated to preserve a complete 360° phase range, with quasi-linear and parallel phase responses over a reasonable frequency band, in spite of this small size. The phase cycle successively uses two different printed elements with complementary capacitive and inductive responses. The studied techniques aim at increasing the insufficient inductive effect. As a demonstration, a 1877-element reflectarray is fabricated with the technique compatible with a single-substrate fabrication process. Measured results show a 1 dB gain bandwidth of 11.3%.Makdissy, T.; Gillard, R.; Fourn, E.; Ferrando Rocher, M.; Girard, E.; Legay, H.; Le Coq, L. (2016). "Phoenix' reflectarray unit cell with reduced size and inductive loading. IET Microwaves Antennas and Propagation. 10(12):1363-1370. doi:10.1049/iet-map.2015.0626S13631370101

Influence of NaX (X=I or Cl) additions on GeS2-​Ga2S3 based glasses

International audienceChalcogenide glasses in the pseudo-​ternary system NaX-​GeS2-​Ga2S3 (X=Cl or I) were synthesized. Different series were investigated in order to highlight the influence of the sodium halide addn. on two different host glasses (GeS2)​80(Ga2S3)​20 and (GeS2)​72(Ga2S3)​28. Macroscopic properties including d. and characteristic temps., such as glass transition temps. Tg and crystn. temp. Tx, were detd. for a max. molar content of NaX equal to 15​%. The evolution of the optical band-​gap and the chem. stability following the compn. were also studied. Cond. measurements were also performed and compared to other Li-​based GeS2-​Ga2S3 glasses. The results were discussed taking into account the cation and anion nature and also the glass packing d

Experimenting an optical second with strontium lattice clocks

Progress in realizing the SI second had multiple technological impacts and enabled to further constraint theoretical models in fundamental physics. Caesium microwave fountains, realizing best the second according to its current definition with a relative uncertainty of 2-4x10^(-16), have already been superseded by atomic clocks referenced to an optical transition, both more stable and more accurate. Are we ready for a new definition of the second? Here we present an important step in this direction: our system of five clocks connects with an unprecedented consistency the optical and the microwave worlds. For the first time, two state-of-the-art strontium optical lattice clocks are proven to agree within their accuracy budget, with a total uncertainty of 1.6x10^(-16). Their comparison with three independent caesium fountains shows a degree of reproducibility henceforth solely limited at the level of 3.1x10^(-16) by the best realizations of the microwave-defined second.Comment: 9 pages, 4 figures, 2 table

Reuse of medical face masks in domestic and community settings without sacrificing safety: Ecological and economical lessons from the Covid-19 pandemic

The need for personal protective equipment increased exponentially in response to the Covid-19 pandemic. To cope with the mask shortage during springtime 2020, a French consortium was created to find ways to reuse medical and respiratory masks in healthcare departments. The consortium addressed the complex context of the balance between cleaning medical masks in a way that maintains their safety and functionality for reuse, with the environmental advantage to manage medical disposable waste despite the current mask designation as single-use by the regulatory frameworks. We report a Workflow that provides a quantitative basis to determine the safety and efficacy of a medical mask that is decontaminated for reuse. The type IIR polypropylene medical masks can be washed up to 10 times, washed 5 times and autoclaved 5 times, or washed then sterilized with radiations or ethylene oxide, without any degradation of their filtration or breathability properties. There is loss of the antiprojection properties. The Workflow rendered the medical masks to comply to the AFNOR S76-001 standard as “type 1 non-sanitory usage masks”. This qualification gives a legal status to the Workflow-treated masks and allows recommendation for the reuse of washed medical masks by the general population, with the significant public health advantage of providing better protection than cloth-tissue masks. Additionally, such a legal status provides a basis to perform a clinical trial to test the masks in real conditions, with full compliance with EN 14683 norm, for collective reuse. The rational reuse of medical mask and their end-of-life management is critical, particularly in pandemic periods when decisive turns can be taken. The reuse of masks in the general population, in industries, or in hospitals (but not for surgery) has significant advantages for the management of waste without degrading the safety of individuals wearing reused masks

Improvement of the Gerchberg-Saxton Algorithm Convergence in Phaseless Antenna Measurements via Spherical-Wave Filtering

International audienceThe phaseless characterization of antennas enables configurations with reduced measurement efforts as the phase acquisition is highly sensitive to numerous error sources. However, both the magnitude and phase information are necessary to reconstruct the 3-D radiation pattern of the tested radiating system. The two scans technique allows for accurate phase retrievals from magnitude-only measurements. In this communication, the two concentric spheres setup is considered with a Gerchberg-Saxton (GS) algorithm as a phase retrieval procedure. These methods are known for their convergence problems, the price to pay for the easier, magnitude-only, measurements. A filtering approach is studied to mitigate these effects and a new, more efficient, filter is proposed. A loop of GS runs coupled with filters is shown to improve the radiation pattern reconstruction without much considerations. Validations are led by simulations and experimental data acquired using a commercial system

Phase Retrieval Procedure for Microwave Linear Arrays

International audienceA methodology to solve the phase retrieval problem arising in microwave linear array is proposed. The goal is to recover the complex array excitations from phaseless measurements of the far field. An approach combining convex optimization (to solve the phase retrieval problem) and two measurement runs (to mitigate the ambiguity problem) has been developed and numerically assessed in various representative examples. These results show that under appropriate conditions of noise and sampling, it is possible to uniquely retrieve the complex excitations of linear arrays from phaseless measurements

Design and manufacturing of a high accuracy planar scanner formillimeter wave applications

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