Javier Vazquez

Stability of active magnetoinductive metamaterials

Passive metamaterials suffer from narrow bandwidths and high losses due to limits imposed by causality. Actively loaded metamaterials on the other hand may be designed to overcome these limitations, with the caveat that stability may be difficult to ensure. In this letter, loops with active non-Foster loads, in which resistance, capacitance, and inductance are negative, are arranged in a periodic lattice to form an effective medium with either negative-Re μ or μ-near-zero magnetic properties over a broad range of frequencies. The stability and effective magnetic properties are examined analytically, as well as with numerical simulations. Furthermore, the tradeoffs between stability, bandwidth, and the lower bounds of the permeability are detailed.

Low Profile, Dual-Polarised Antenna for Aeronautical and Land Mobile Satcom

High data rate communications on the move is fastly becoming a major application area for satellite systems using Ku- and higher frequency bands. The ground terminal antenna used in such systems has a profound impact on the system capabilities and is constrained in many often conflicting ways. While simple reflector systems offer the lowest cost solution, there is a widespread need for low profile antennas to minimize the antenna visual signature and to satisfy aesthetic and transportation requirements. It is often considered that the use of such antennas will compromise the system performance.

Analysis of ring and rectangular slot FSS using a new equivalent circuit method

A new method which uses the spatial modal decomposition of the single FSS element has been applied for the analysis of a thin frequency selective structure (FSS) composed of rectangular slot elements. The method is based on the equivalent circuit approach and has exhibited more accurate results compared with conventional equivalent circuit approaches. In addition the method performs much faster compared to rigorous solutions. A good agreement in comparison with other methods and measurements has been revealed for several kinds of thin FSS.

Modal decomposition equivalent circuit method application for multilayer FSS

In the previous works a detailed review of existing equivalent circuit methods for the analysis and design of frequency selective surfaces (FSS) has been presented. It has been already shown that the proposed modal decomposition equivalent circuit method (MDECM) offers a higher accuracy and a better physical understanding of an FSS compared with other equivalent circuit methods. The method is based on determining the admittances that relate the voltage and current intensity amplitudes for any incident Floquet mode and is achieved by studying the interaction of plane waves of arbitrary angles of incidence with the structure. An important feature of the technique is that the resulting formulation can be expressed as a multi-tapped ideal transformer connected to a set of mode admittances and approximations can be made to give a very elegant solution, so long as the FSS element aperture field can be well approximated by a simple mode combination. The method has been recently extended to deal with complicated FSS geometry such as multi-frequency and multi-layer structures. It has been found that the method offers even more advantages in simulation time for those structures in comparison with full-wave solutions and computational electromagnetic (CEM) software results. The solution obtained for multilayer structures, has been successfully applied for two layers FSSs of different geometry. Good agreement with other methods results has been obtained. Method advantages and limitations will be discussed in the conclusions.

Broadband active magnetic materials

In this presentation a stable, active metamaterial is demonstrated which can be designed to exhibit either broadband negative-µ or µ-near-zero (µnz) values. Over the last decade a number of applications, including cloaking [1] and tunneling [2] have been proposed which fundamentally rely on the use of materials with negative, or close-to-zero electric and/or magnetic parameters. Despite a host of promising applications, these metamaterials suffer from two inherent limitations: operating at or near resonance they are lossy and narrowbanded [3]. Active metamaterials have been proposed that overcome these natural limitations of their passive counterparts, both at optical [4] and at microwave frequencies [5], [6].

Modal Decomposition Equivalent Circuit Method Application for dual Frequency FSS Analysis

An application of a modal decomposition equivalent circuit method (MDECM) for analysis of more complex structures like dual frequency FSS has been proposed. The method is based on the equivalent circuit approach and has been recently extended to deal with complicated FSS geometry. Now, the method is able to take into account thick dielectric substrates. What is more important, an initial estimation of the field distribution in a slot aperture can be expressed in terms of two modes despite only one in the fundamental method definition. Theoretical study of FSS composed of dual ring slot elements has revealed a good agreement in comparison with CEM software and periodic method of moments (PMM).