Suchergebnisse

Chiral Metamaterials are artificial composite materials exhibiting further properties neither observed in its constituents nor available in the nature, such as negative refractive indices or high polarization plane rotations, or enhancing the composite features relative to the individual properties of its constituents. In this communication a comparative parametric study of different plane chiral metamaterials presenting 3D chirality is performed. The obtained results show how rosette-type structures are more appropriate to improve the rotation of the polarization plane whereas specular-type assemblies are more suitable for obtaining broader band widths. Finally, the application of these structures as antenna plane covers for enhancing the antenna gain and axial ratio is also examined. ; This work has been partially supported by the Spanish Government MINECO through the Research Projects CONSOLIDER CSD2008-00066 EMET and TEC2010-21496-C03-01.

Chiral metamaterials (CMMs) are widely used to implement devices that transform the polarization of an incident electromagnetic wave, such as polarization rotators and linear to circular converters, but rarely used as circular polarization converters. This letter presents a CMM that changes the handedness of a circularly polarized incident wave. This structure, which presents subwavelength thickness, provides polarization conversion with independence on both the front and back directions and the handedness of the incident wave. High polarization conversion efficiency is shown by both simulations and experiments. ; This work has been partially supported by the Spanish Government MINECO through the FEDER co-funded Research Project TEC2014-55463-C3-3-P and the Research Project TEC2012-33321.

Planar superstrates constituted by Chiral Metamaterials structures can transform the radiation properties of an antenna. In this communication, an asymmetric chiral metamaterial based structure is proposed. Due to the lack of C4 symmetry in the design, the transmission coefficients depend on the incident wave polarization and display high transmission for one circular polarization but low transmission for the other one. The proposed structure is then used to improve the radiation characteristics of a microstrip patch antenna. Taking advantage of the properties of the asymmetric chiral structure, the polarization of the radiated field is modified, transforming the linear polarization of the microstrip antenna into a circular one. ; This work has been partially supported by the Spanish Government MINECO through the FEDER co-funded Research Project TEC2014-55463-C3-3-P and the Research Project TEC2012-33321.

This communication presents a novel diode switchable chiral metamaterial structure that manipulates the polarization in different ways depending on the active bias lines. Three different bias states that provide three totally different behaviors have been considered: polarization rotator, circular polarization converter and linear to circular converter. ; This work has been partially supported by the Spanish Government MINECO through the ERDF co-funded Research Projects TEC2014-55463-C3-1-P, TEC2014-55463-C3-2-P and TEC2014-55463-C3-3-P.

Negative refraction has many potential applications in the information and communications technology field. However, the high losses of most negative refraction materials prevent the use of this novel property in the implementation of practical devices in the HF range. In an attempt to overcome this inconvenience, we present two gammadion-fishnet chiral metamaterial structures, constituted by the combination of a lossy chiral metamaterial and different fishnet structures. The electromagnetic characterization of the proposed metamaterials provides a larger bandwidth with negative refraction as well as lower losses when compared with the initial structures. The results were obtained by using both numerical and experimental data, which support our designs. ; This work has been partially supported by the Spanish Government MINECO through the ERDF co-funded Research Projects TEC2014-55463-C3-1-P and TEC2014-55463-C3-3-P, PGC2018-098350-B-C21 and PGC2018-098350-B-C22.

In this work a composed chiral metamaterial structure constituted by the combination of a composite chiral metamaterial and a modified fishnet structure is presented and numerically analyzed. This new fishnet-like chiral metamaterial features two wide frequency bands wherein the refractive indices are negative and exhibits lower losses than its constituents do. ; This work has been partially supported by the Spanish Government MINECO through the ERDF co-funded Research Projects TEC2014-55463-C3-1-P and TEC2014-55463-C3-3-P.

In this communication the authors present a novel chiral metamaterial structure formed by planar omega particles These omega particles, arranged in conjugated pairs, present high optical activity. Thanks to the high values of chirality, the structure provides negative refractive index with high figure of merit. ; This work has been supported by the Spanish Government MINECO through the Research Projects TEC2014-55463-C3-1-P, TEC2014-55463-C3-3-P and by the European Commission (ERDF).

This work presents the development of a W-band planar antenna array, starting from the study of a single element, evaluating the effect of a chiral cover on it, then incrementing to the design, fabrication and measurements of a W-band linear array of three planar antennas. Each radiating element is a patch fed by slots. This technology is cheap and affordable. Simulation fits quite well with measurements. Metamaterial may enhance the radiation properties, particularly, the directivity. The chiral metamaterial cover is made of two layers of mutually twisted planar metal rosettes in parallel planes. ; The authors would like to thank to Sandra Pana for the fabricated samples of the available prototype and to Dermot Erskine for the correction of the text. This work has been partially supported by the MINECO of Spanish Government through the Research Projects CONSOLIDER CSD2008-00068 and CSD2008- 00066, FEDER co-funded TEC2011-29126-C03- 01, TEC2011-29264-C03-01 and TEC2010- 21496-C03-01.

This work presents the design, fabrication and measurements of a W-band linear array of planar antennas. The structure of the antenna, which presents as benefit low cost and easy manufacture, is composed of three planar patches fed by slots. The simulation and the experimental results are compared showing a good agreement. In order to enhance the radiation properties, a chiral metamaterial cover is added to the antenna array. The chiral meta material cover is formed by two layers of mutually twisted planar metal rosettes in parallel planes and it is expected to enhance the directivity of the antenna array. ; This work has been partially supported by the MINECO of Spanish Government through the Research Projects CONSOLlDER CSD2008-00068 and CSD2008-00066, FEDER co-funded TEC2011-29126-C03-01 and TEC2010-21496-C03-01

In this paper, the multipactor RF breakdown in a parallel-plate waveguide partially filled with a ferrite slab magnetized normal to the metallic plates is studied. An external magnetic field is applied along the vertical direction between the plates in order to magnetize the ferrite. Numerical simulations using an in-house 3D code are carried out to obtain the multipactor RF voltage threshold in this kind of structures. The presented results show that the multipactor RF voltage threshold at certain frequencies becomes considerably lower than for the corresponding classical metallic parallel-plate waveguide with the same vacuum gap. ; This work was supported by the European Space Agency (ESA) under Novel Investigation in Multipactor Effect in Ferrite and other Dielectrics used in high power RF Space Hardware Contract AO 1-7551/13/NL/GLC, and partially by the Spanish Government (under coordinated R&D projects TEC2013-47037-C5-R and TEC2014-55463-C3-3-P).

This paper reports on the experimental measurement of power threshold levels for the multipactor effect between samples of ferrite material typically used in the practical implementation of L- and S-band circulators and isolators. For this purposes, a new family of wideband, nonreciprocal rectangular waveguide structures loaded with ferrites has been designed with a full-wave electromagnetic simulation tool. The design also includes the required magnetostatic field biasing circuits. The multipactor breakdown power levels have also been predicted with an accurate electron tracking code using measured values for the secondary electron yield (SEY) coefficient. The measured results agree well with simulations, thereby fully validating the experimental campaign. ; This work was supported by European Space Agency (ESA) through research project "Novel Investigation in Multipactor Effect in Ferrite and other Dielectrics used in High Power RF Space Hardware" (ref. AO 1-7551/13/NL/GLC), and by MINECO (Spanish Government) under R&D projects TEC2016-75934-C4-1-R, TEC2016-75934-C4-2-R and the ERDF co-funded project TEC2014-55463-C3-3-P.