A modal-based iterative circuit model for the analysis of CRLH leaky-wave antennas comprising periodically loaded PPW

A novel modal-based iterative circuit model is described for the calculation of the complex propagation constant of mushroom-like parallel-plate composite right/left handed leaky-wave antennas (PPW CRLH LWAs). The conventional lossless CRLH unit cell circuit is modified in order to consider the electromagnetic coupling to free space through a slot. For this purpose, a slot equivalent radiative structure, based on phased-array theory, is analyzed using a mode matching approach combined with Floquet's theorem. A direct correspondence between lumped elements and this radiative structure is found, leading to a frequency-dependent unit cell circuit model. A quickly converging iterative algorithm is then employed to determine the final element values of the unit cell. The proposed method is accurate, and it takes into account the structure physical dimensions. It also allows to obtain a balanced CRLH unit cell design without requiring any full-wave simulation, is several orders of magnitude faster than full-wave simulations, and provides a deep insight into the physics of the antenna radiation mechanism.Ministerio de Educación y Ciencia, Ref. TEC2010-21520-C04-0

Antenas CRLH LWA basadas en guía de onda: análisis teórico y demostración experimental

A novel composite right/left-handed leaky-wave antenna (CRLH LWA), based on periodically loaded parallel-plate waveguides (PPW) is presented. The loading is obtained by a rectangular grid of vertical wires and parallel slots etched in the upper metal plane of the PPW. A novel modal-based iterative circuit is proposed for the complete analysis and design of this type of antennas. The coupling between the antenna and freespace is rigourously modeled using a mode-matching technique, combined with the Floquet’s theorem. This provides a lossy dispersive CRLH unit-cell model, whose values are obtained using a quickly-convergent iterative algorithm. The proposed method is accurate, extremely fast and it takes into account the structure physical dimensions. A CRLH PPW LWA has been designed (without requiring any time consuming full-wave simulation), analyzed and fabricated using the proposed method. Very good agreement has been found between measurements and simulations, validating both, the antenna radiating phenomena and the proposed technique.Este trabajo ha sido cofinanciado por el Ministerio de Educación y Ciencia (Proyecto: TEC2007-67630-C03-02, Beca: FPU-AP2006-015)

Q-Band Millimeter-Wave Antennas: An Enabling Technology for MultiGigabit Wireless Backhaul

[EN] The bandwidth demands in mobile communication systems are growing exponentially day by day as the number of users has increased drastically over the last five years. This mobile data explosion, together with the fixed service limitations, requires a new approach to support this increase in bandwidth demand. Solutions based on lower-frequency microwave wireless systems may be able to meet the bandwidth demand in a short term. However, with the small-cell mass deployment requiring total capacities of 1 Gb/s/km2, scalable, multigigabit backhaul systems are required. Millimeter-wave technology fits nicely into these new backhaul scenarios as it provides extended bandwidth for high-capacity links and adaptive throughput rate, which allows efficient and flexible deployment. Besides these advantages, millimeter-wave solutions become even more attractive when the cost of backhaul solutions and the cost of spectrum licenses are factored in. Compared to the cost of laying fiber to a cell base station, which is the only other scalable solution, the millimeter-wave solution becomes the most appropriate approach.The research leading to these results received funding from the European Commission's seventh Framework Programme under grant agreement 288267.Vilar Mateo, R.; Czarny, R.; Lee, ML.; Loiseaux, B.; Sypek, M.; Makowski, M.; Martel, C.... (2014). Q-Band Millimeter-Wave Antennas: An Enabling Technology for MultiGigabit Wireless Backhaul. IEEE Microwave Magazine. 15(4):121-130. https://doi.org/10.1109/MMM.2014.2308769S12113015

Experimental demonstration of metamaterials application for mitigating scan blindness in phased array antennas

This paper presents two metamaterial-inspired solutions to mitigate the scan blindness effects in a phased array antenna. In the first solution, portions of a bed of nails are introduced in the radome to prevent the excitation of surface waves. In the second solution, a superstrate metasurface is designed to synthesize a permittivity tensor optimized to achieve a wide angle impedance matching. In both approaches, the numerical simulations are successfully compared with measurements of a phased array antenna prototype with 100 elements. The wire medium-based solution reveals an effective way for reducing the blind-spot in a wide bandwidth, while the metaradome has been found less suitable for the same purpose.This work was supported by the METALESA project A-1089- RT-GC that was coordinated by the European Defence Agency (EDA) and funded by 11 contributing Members (Cyprus, France, Germany, Greece, Hungary, Italy, Norway, Poland, Slovakia, Slovenia and Spain) in the framework of the Joint Investment Programme on Innovative Concepts and Emerging Technologies (JIP-ICET)

Diagnosis and treatment of pediatric acquired aplastic anemia (AAA): An initial survey of the North American Pediatric Aplastic Anemia Consortium (NAPAAC)

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106711/1/pbc24875.pd

Pseudoknot structures with conserved base triples in telomerase RNAs of ciliates

Telomerase maintains the integrity of telomeres, the ends of linear chromosomes, by adding G-rich repeats to their 3′-ends. Telomerase RNA is an integral component of telomerase. It contains a template for the synthesis of the telomeric repeats by the telomerase reverse transcriptase. Although telomerase RNAs of different organisms are very diverse in their sequences, a functional non-template element, a pseudoknot, was predicted in all of them. Pseudoknot elements in human and the budding yeast Kluyveromyces lactis telomerase RNAs contain unusual triple-helical segments with AUU base triples, which are critical for telomerase function. Such base triples in ciliates have not been previously reported. We analyzed the pseudoknot sequences in 28 ciliate species and classified them in six different groups based on the lengths of the stems and loops composing the pseudoknot. Using miniCarlo, a helical parameter-based modeling program, we calculated 3D models for a representative of each morphological group. In all cases, the predicted structure contains at least one AUU base triple in stem 2, except for that of Colpidium colpoda, which contains unconventional GCG and AUA triples. These results suggest that base triples in a pseudoknot element are a conserved feature of all telomerases

Clustering heterochromatin: Sir3 promotes telomere clustering independently of silencing in yeast

Arrays of Sir3 binding sites at telomeres are sufficient to promote long-range trans-telomere interactions

Towards a new image processing system at Wendelstein 7-X: From spatial calibration to characterization of thermal events

Wendelstein 7-X (W7-X) is the most advanced fusion experiment in the stellarator line and is aimed at proving that the stellarator concept is suitable for a fusion reactor. One of the most important issues for fusion reactors is the monitoring of plasma facing components when exposed to very high heat loads, through the use of visible and infrared (IR) cameras. In this paper, a new image processing system for the analysis of the strike lines on the inboard limiters from the first W7-X experimental campaign is presented. This system builds a model of the IR cameras through the use of spatial calibration techniques, helping to characterize the strike lines by using the information given by real spatial coordinates of each pixel. The characterization of the strike lines is made in terms of position, size, and shape, after projecting the camera image in a 2D grid which tries to preserve the curvilinear surface distances between points. The description of the strike-line shape is made by means of the Fourier Descriptors

Forward modeling of collective Thomson scattering for Wendelstein 7-X plasmas: Electrostatic approximation

In this paper, we present a method for numerical computation of collective Thomson scattering (CTS). We developed a forward model, eCTS, in the electrostatic approximation and benchmarked it against a full electromagnetic model. Differences between the electrostatic and the electromagnetic models are discussed. The sensitivity of the results to the ion temperature and the plasma composition is demonstrated. We integrated the model into the Bayesian data analysis framework Minerva and used it for the analysis of noisy synthetic data sets produced by a full electromagnetic model. It is shown that eCTS can be used for the inference of the bulk ion temperature. The model has been used to infer the bulk ion temperature from the first CTS measurements on Wendelstein 7-X

Modellierung konformer Apertur-Gruppenantennen mit Mode-Matching und hybriden Boundary-Element-Method-, Mode-Matching-Verfahren

This work deals with the theoretical principles of two exact methods (full-wave methods) for the electromagnetic computer-aided design of conformal array antennas. Typical configurations of antenna elements on curved surfaces are investigated based on these methods. With respect to the available electromagnetic modelling methods conformal array antennas are divided into two classes. The distinction is drawn depending on the existence of analytical modal solutions of the boundary value problem given by the carrier structure. In case of the existence of an analytical solution it is possible to develop a very efficient partly analytical modelling method. Otherwise, a general fully numerical method has to be applied, which does not make any assumptions about the carrier structure. Thus, two different methods are presented. The first part of this work deals with a method for sector arrays of waveguide-fed aperture elements on circular metal cylinders. Concentric layers of homogeneous materials may be placed both outside the metal cylinder and inside the feeding waveguides. The modelling method is based on the use of generalized scattering matrices, which are set up by a "mode-matching" (MM) technique. A pattern synthesis method, which is essential with respect to the application of the array antenna, is also presented. It is based on an invertive mathematical approach and due to the modelling by a full-wave method all physical effects introduced by the antenna configuration are implicitly taken into account. The software, which has been developed based on this approach, can be used for investigations on radiation properties (pattern synthesis), as well as element matching, mutual coupling and - using a cylindrical wave transformation - scattering (RCS or SW). The second part of this work presents the basics of a fully numerical hybrid method for the design of waveguide-fed aperture elements embedded into arbitrarily shaped metal surfaces. The metal surfaces are modelled by a boundary integral method called "boundary element method" (BEM). A magnetic field integral equation (MFIE) is set up and solved numerically by a method of moments (MoM). Surfaces with small radii of curvature are efficiently modelled by an extension of the classical formulation of the BEM. The apertures are included in this formulation by a novel combination of the integral equation method with a "mode-matching" (MM) technique. This combination can be called "hybrid BEM/MM" and may be applied to the investigation of radiation, mutual coupling and scattering problems taking into account the complete antenna configuration including the arbitrarily shaped carrier structure