Álvaro Gómez

Full-Wave Hybrid Technique for 3-D Isotropic-Chiral-Material Discontinuities in Rectangular Waveguides: Theory and Experiment

Numerical results obtained using a full-wave hybrid technique (comprising a new formulation of the coupled-mode method and the mode-matching method) for treating 3-D isotropic- chiral-material discontinuities in rectangular wave guides with perfect electrically conducting walls were compared with experimental data. For that purpose, samples of an isotropic chiral material were manufactured as composite materials. These samples were then fully characterized in the X-band. The measured constitutive parameters were used in the full-wave hybrid technique to predict the scattering parameters of three different structures-each a waveguide filled partially with the isotropic chiral material. The scattering parameters were also measured. The predicted and measured scattering parameters were in reasonably good agreement.

On One- and Two-Dimensional Electromagnetic Band Gap Structures in Rectangular Waveguides at Microwave Frequencies

Electromagnetic band gap (EBG) structures of two different configurations implemented inside R120 rectangular waveguides (frequency range 10–15 GHz) are examined. The first configuration has a periodic, piecewise uniform variation of permittivity in the propagation direction. Two types of such one-dimensional (1D) EBG structures are analyzed, one with the unit cell comprising two dielectric layers, the other with three dielectric layers per unit cell. The second configuration is two-dimensional, with the unit cell along the propagation direction containing two sections, each of which is made of alternating pillars of two dielectric materials. The Bloch theorem is invoked for the ideal EBG structures, which are infinitely long in the propagation direction. The mode-matching method (MMM) is used for real 1D-EBG structures, which contain a finite number of unit cells, whereas a combination of the coupled-mode method (CMM) and the MMM is used for real 2D-EBG structures. Spectrums of the transmission coefficient of the fundamental mode for the 1D-EBG structures are computed and shown to compare favorably against experimental data. The effect of inserting a defect in 1D-EBG structures is demonstrated theoretically as well as experimentally. The band gaps computed for real and ideal 2D-EBG structures are compared as well.

Multipactor Effect in a Parallel-Plate Waveguide Partially Filled With Magnetized Ferrite

The aim of this paper is the analysis of the multipactor effect in a parallel-plate waveguide when a ferrite slab, transversally magnetized by a static magnetic field parallel to the waveguide walls, is present. Employing an in-house developed code, numerical simulations are performed to predict the multipactor radio frequency voltage threshold in such a ferrite-loaded waveguide. Variations of the ferrite magnetization field strength and the ferrite slab height are analyzed. Effective electron trajectories are also shown for a better understanding of the breakdown phenomenon, finding different multipactor regimes.

Analysis of Multipactor RF Breakdown in a Waveguide Containing a Transversely Magnetized Ferrite

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 3-D 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.

Design and fabrication of a W-band linear array of planar antennas and study for the enhancement of its radiation properties with a chiral metamaterial cover

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 metamaterial 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.

Novel fishnet-like chiral metamaterial structure with negative refractive index and low losses

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.

Chiral media characterization using both linear and circular polarized waves

A new free-wave experimental method for chiral media characterization is presented. The setup is based on a pair of dual horn antennas and a diplexer 90° phase shifter, which allows to produce both circularly and linearly polarized waves and to measure the co- and cross-polar components of the transmission and reflection coefficients of a chiral slab under normal illumination. Then, six experimental measurements are available to retrieve three constitutive parameters. Furthermore, by including the reflection coefficient of the backed metal sample an over determined system of equations is obtained, which leads to increase the accuracy of the material characterization.

Diode switchable chiral metamaterial structure for polarization manipulation

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.

Novel multipactor studies in RF satellite payloads: Single-carrier digital modulated signals and ferrite materials

In this work it is reviewed the most novel advances in the multipactor RF breakdown risk assessment devoted to RF satellite microwave passive devices employed in space telecommunication systems. On one side, it is studied the effect of transmitting a single-carrier digital modulated signal in the multipactor RF voltage threshold in a coaxial line. On the other hand, an analysis of the multipactor phenomenon in a parallel-plate waveguide containing a magnetized ferrite slab it is presented.

Green's formulation for chirowaveguides

A Green integral formulation of the boundary value problem in chirowaveguides with translational symmetry and the application to the rectangular case are presented in this paper. The Green equations for the two eigenmodes in unbounded chiral media, i.e. right and left circularly polarized waves, are formulated in terms of the Hankel functions. By splitting the waveguide contour into a finite number of intervals, the equations are discretized and a homogeneous system of equations can be obtained. The number of unknowns is reduced to the half by applying the relations between the longitudinal components and their normal derivatives at the metallic contours. The method has been used for modeling the rectangular waveguide and the dispersion diagram and the field structure for some propagation modes are presented.