Ratiba Benzerga

Highly tunable microwave stub resonator on ferroelectric KTa0.5Nb0.5O3 thin film

A coplanar waveguide (CPW) stub resonator has been fabricated on a pulsed-laser deposited KTa(0.5)Nb(0.5)O(3) (KTN) thin film (600 nm-thick) onto a r-plane sapphire substrate. It was designed to operate at 10 GHz when the applied bias voltage is zero. We show experimentally that the resonance frequency is shifted by 44% under a 70 kV/cm DC applied electric field. In addition, the dielectric characteristics of the KTN film have been assessed through post-processed measurements of CPW 50-Omega transmission lines using the conformal mapping method.

Cooperative communications between vehicles and intelligent road signs

CAPTIV is a research program proposing new low-cost and energy-efficient mobile communications solutions to ease and make safer road traffic conditions. Considering ¿intelligent¿ road signs and vehicles, i.e. equipped with an autonomous radio communication system, drivers will be able to receive at any time various information about traffic fluidity or road sign identification. In order to reduce deployment cost and increase lifetime of the whole system, Multi-Input Multi-Output (MIMO) signal processing techniques are used. Considering each crossroads as a communication node, the possible cooperation between road signs allows energy-efficient communications between crossroads. MIMO channels characterization and modeling, specific antennas conception, associated with signal processing techniques allow to further optimize the energy consumption between nodes. A driving simulator is used in order to both validate the communication system and protocols between vehicles and road signs and evaluate the effect of the additional information on the driver behavior. Supported by the Brittany Regional Council, CAPTIV is a highly applicative program. A first prototype of such a communicating crossroads will be presented in the Vehipole in Saint-Brieuc (technological site devoted to ITS experimentations).

Straight wedge absorber geometry optimization for normal and oblique incidence

This paper presents a topology for improving the performance of straight wedge absorbing materials at oblique angles of incidence. The optimization process is based on a genetic algorithm and allows one to obtain a low reflection coefficient within a wide band of frequencies. We investigate the performance by comparison between the straight wedge absorber and the optimized wedge absorber. These wedge absorbers were simulated in the CST Microwaves Studio software, using a polymer foam material.

Ferroelectric tunability: From characterization to telecomunication application

Advanced dielectric spectroscopy enables studying of the ferroelectric complex permittivity. Interpretation with the hyperbolic law provides a better fundamental understanding of the materials tunability: bulk contribution, domain wall vibration and displacements may be discerned. Applications, like mobile telecommunication terminals may profit for the design of miniaturized and tunable antennas. As an example, conception and realization of a notch slot antenna with an integrated ferroelectric thin film varactor is presented.

A dielectric resonator antenna (DRA) reflectarray

This paper presents the design of a Ka-Band dielectric resonator antenna (DRA) reflectarray working at 30 GHz. The unit-cell is based on a DRA loaded by a metallic strip printed on the top surface. By varying the strip length, the desired phase variation is achieved. The DRA reflectarray consists of 24×24 unit-cells and is compatible with monolithic fabrication. A full-wave FDTD modelling is performed to simulate the whole antenna and validate a simplified calculation that can be used to predict the antenna performance.

Dielectric resonator antenna reflectarray in Ka-band

A reflectarray antenna combines some of the best features of reflector antennas and phased array antennas [1]. It consists of a primary source illuminating a planar surface composed of many unit-cells. By varying the parameters of each cell, it is possible to control the main beam direction and shape the beam. Many prototypes in microstrip technology have been proposed recently [2,3]. Nevertheless, at millimeter waves, the conductor losses become severe, and the antenna efficiency may drop significantly. On the other hand, dielectric resonator antennas (DRAs) have been introduced due to their low loss, relatively wide bandwidth and high radiation efficiency [4]. Due to these advantages, a first DRA reflectarray was developed in Ka-Band in [5]; in that work, the required phase delay was achieved by varying the DRA length, and the reflectarray was made of DRA blocks of various size. We have introduced recently an alternative solution based on strip-loaded DRAs [6]. In this design, the desired phase delay is only controlled by the length of the metallic strip printed on top of constant-size DRA; this concept has been validated experimentally in C-band in waveguide simulators [6]. In this paper we apply similar ideas in Ka-band (30 GHz), and we present the design and measurement of a complete 24×24-element reflectarray.

Loss reduction technique in ferroelectric tunable devices by laser micro-etching. Application to a CPW stub resonator in X-band

Ferroelectric materials are known to be lossy at microwaves. A local microetching technique based on laser ablation is implemented here to reduce the insertion loss of highly tunable devices fabricated on KTa1-xNbxO3 (KTN) ferroelectric thin films. The relevance of this approach is studied in X-band by comparing numerically and experimentally the performance of a frequency-tunable coplanar waveguide stub resonator before and after KTN microetching. The experimental data demonstrate a large loss reduction (by a factor 3.3), while keeping a high-frequency tunability (47%) under a moderate biasing static electric field (80 kV/cm). This approach paves the way for the design of ferroelectric reconfigurable devices with attractive performance in X-band and even beyond.

Synthesis and Structural Characterization of Glass Foam Composites for Electromagnetic Application

This article deals with the synthesis and structural characterization of glass foams made from cullet and loaded with carbon fibers or used tires for electromagnetic absorption application. All the raw materials used for this work come from recycling or reconditioning. Two carbonaceous loads are tested; the carbon fiber scraps are used because they show an interest in the field of absorption and parallel to this, another load type (tire waste) is used for its high carbon content. This novel later load is used, to our knowledge, for a first time. Samples with different weight contents of the loads are achieved and characterized. The used percentages of loads, are respectively, between 0 and 10 wt.% and between 0 and 20 wt.% for carbon fibers and tire waste. In this article, we present and discuss the elaboration method, the morphological and structural results of the loaded glass foam composites. A low density was obtained from both composite, with a density between 0.28 and 0.53 g/cm3. An excess content of tire waste load leads to “collapse” of the gas bubbles during the heat treatment of the sample which induces an increase in the density of the composite. This is due to the decomposition of this load during the elaboration process. This result is confirmed by the scanning electron microscopy observation and also by gravimetric thermal analysis of the tire waste. Contrary to this, composites loaded with carbon fibers show better structure homogeneity and non-decomposition of carbon fibers during a heat treatment.

Method for material characterization in a non-anechoic environment

This paper presents a characterization method for extracting the reflection coefficient of materials and the real part of their permittivity. The characterization is performed in a real environment, as opposed to the classical measurement methods that require an anechoic chamber. In order to reduce the effects of the multipath propagation, a free space bistatic measurement was performed at different distances material-antennas in far field. By using a Teflon sample and a commercial absorbing material sample, measurements have been performed in order to validate the characterization technique.