Smail Tedjini

Experimental investigation on the optical unbalanced Mach-Zehnder interferometers as microwave filters

In this work, we study the propagation effects of a modulated lightwave signal in an unbalanced Mach-Zehnder interferometer (UMZI). Experimental results of the microwave frequency response of the structure are obtained using two lightwave network analyzers HP8702A and HP8510B with an optoelectronic HP83420A. It is shown that such an optical device could be used to perform a number of interesting microwave applications. The problems appearing in the coherent working regime and the possibility of integrated device realizations for millimeter-frequency signal processing are also discussed.<<ETX>>

Measurement & Calibration Procedure for the Characterization of the Scattering Parameters in Microwave Fiber-Optic Devices

A new measurement procedure is developed for the determination of optoelectronic scattering parameters in fiber-optic devices working in microwave modulating frequency range. The measurement scheme is based on a microwave network analyzer and optoelectronic transducers to determiine the optical parameters by the use of corresponding electrical parameters. The application of the TMR (Through, Match, Reflect) calibration procedure for optical measurements is straightforward, which requires for the realization of the needed optical standards only commercially available elements. The error removal can be performed in a wide modulating frequency range both in transmission and reflection measurements. The validity of this measurement calibration procedure is demonstrated by some measurement examples.

Determination of measurement uncertainties applied to the RCS and the differential RCS of UHF passive RFID tags

Measurement methodology and theoretical equations to RCS and ΔRCS determination are recalled and the measurement uncertainties are evaluated in this paper. Even if measurement uncertainties are generally not required for RFID, it is important to understand and to be able to determine the measurement uncertainty. Currently, manufacturers and testing laboratories present some results of RFID measurements but never show the associated uncertainty. Yet, seeing the values of the uncertainties, it is clear that they are not negligible.

TLM Analysis of Finline T-Junctions for Computer-Aided Design

This paper presents a circuit model of a T-junction in bilateral finline. The elements of this model, which is suitable for CAD, have been determined with the Modified Transmission Line Matrix (MTLM) method of numerical analysis. This procedure amounts to simulating measurements of S-parameters on a computer by field analysis in the time domain.

Measurement of RCS and reading range of UHF tags in free space and with wood support

This communication introduces measurement results of Radar Cross Section (RCS) of UHF passive tags. The RCS theory and its relationship with the reading range of tags are explained. We studied the influence of tag support, particularly those made of wood. Finally, we found that RCS is a good parameter to determine homogeneity of multiple tags of the same industrial mass production.

A New Design of a Broadband Microwave Test Fixture for Odd Mode Excitation in Monolithic Coplanar Coupled Strips

In this paper, we present the design and performances of a precision microwave test fixture suitable for odd mode excitation in both monolithic and coplanar coupled strips (CPS). The proposed test fixture is based on a new type of a broadband coaxial-to-CPS transition. The test fixture was used to measure the Sij parameters of a GaAs monolithic CPS in the 2-18 GHz frequency range. Some time domain reflectometry results are presented.

Une nouvelle ligne intégrable millimétrique: la ligne à ailettes

AnalyseLa ligne à ailettes (ou fin-line) est une nouvelle ligne pour les ondes millimétriques. Dans cet article, les auteurs font une mise au point sur les recherches accomplies afin d’étudier cette ligne. Ils présentent une étude théorique assez détaillée de cette ligne en utilisant la méthode spectrale. La caractéristique de dispersion, l’impédance caractéristique, la fréquence de coupure et la distribution de puissance sont étudiées. La méthode converge rapidement, les résultats théoriques sont confrontés à quelques résultats expérimentaux. L’accord est très satisfaisant.AbstractThe fin-line structure is a special printed transmission line for millimeter wave integrated circuits. In this paper, a comparison between fin-line and other lines like waveguide and microstrip is presented. The spectral domain approach is used to determine the properties of the fin-line. The dispersion curves, characteristic impedance and power distribution are presented. The numerical solution converges rapidly in all the cases investigated. Some experimental results are reported. The agreement of measured and computed results is very satisfactory.

Modeling of discontinuities on lossy planar microwave structures by the spectral domain approach

New components appear, that require an improvement in the modeling methods in the microwave field. Indeed, in order to model the working of components such as the photoelectrical switch, whose substrate conductivity varies under the action of a judiciously chosen light beam, it has proved that taking losses in 3D problem was required. Thus, we have coupled the complex frequency concept to a dynamic modeling method: the spectral domain approach. This concept lays on the fact that the resonance frequency of a lossy resonator is complex. It enables to get the quality factor of the resonator and then its equivalent circuit, including the resistive elements that are characteristics of the losses. In the case of low losses, this general principle can be used through a perturbation method. We develop here this principle and use it for the study of a photoelectrical switch.RésuméL’apparition de nouveaux composants demande une amélioration des méthodes de modélisation en microondes. En effet, pour modéliser le fonctionnement d’un composant tel que le commutateur photoélectrique, dont le substrat voit sa conductivité se modifier sous l’action d’un faisceau lumineux adéquat, il s’est avéré nécessaire de pouvoir prendre en compte les pertes dans les problèmes 3D. Pour ce faire, nous avons couplé le concept de fréquence de résonance complexe à une méthode de modélisation dynamique : la méthode spectrale. Ce concept repose sur le fait que la fréquence de résonance d’un résonateur à pertes est complexe. Elle permet de remonter au facteur de qualité du résonateur et donc à son schéma électrique équivalent, y compris les éléments résistifs caractéristiques des pertes. Il est possible de tirer parti avantageusement du cas de pertes faibles, pour lequel le cas général peut être utilisé au moyen d’une méthode de perturbation, allégeant ainsi la modélisation. Ce principe est développé et exploité pour l’étude d’un commutateur photoélectrique.

On the use of optical networks for performing microwave functions

This communication considers the use of optical networks excited by a light signal modulated at microwave frequencies in order to perform microwave functions. Using some basic single mode optical fibre elements at 1.3 ¿m we have realised an unbalanced Mach-Zehnder interferometer that can be used as a microwave band rejection filter. The experimental results show good performances with a rejection ratio higher than 40 dB and a very good phase linearity.

On the Research of Non Reciprocal Fin-Line Devices

In this paper, a semiconductor based fin-line isolator is analyzed. This device is based on field displacement effect phenomenon arising in a gyroelectric semiconductor (a theoretical method is presented). It is mainly an extension of the well known spectral domain approach. For this purpose, the semiconductor layer is taken into account through its conductivity tensor. Two semiconductors (GaAs and InSb) have been considered. The main parameters of the isolator such as isolation, insertion losses, band width are computed and compared with the experimental results. There is satisfactory agreement between theoretical and experimental results in the case of the GaAs. Finally it is pointed out that the InSb is the best choice.