Jacques David

Antenna Ultra Wideband Enhancement by Non-Uniform Matching

In this paper, antenna ultra wideband enhancement by non-uniform matching is proposed. The antenna consisted of a rectangular shaped radiator with two convex circled corners. Simulated results using CST Microwave Studio and measured results of a fabricated antenna concord well to prove that it can operate from about 3.5 GHz to 4.6 GHz and from 7.4 GHz to 12.7 GHz for S11(dB) <-10 dB. In addition, a good impedance matching is noted in the IEEE radar engineering X band range since the return loss coefficient remains below -50 dB value at 9.5 GHz and can reach -45 dB at 11 GHz. A current density comparison at 11 GHz, supporting our argument, between a stepper corner and convex corner demonstrates that the current density can reach 52A/m with a convex corner whereas it does not exceed 33A/m for the antenna with a stepper corners. Radiation patterns at various frequencies and peak gains show clearly interesting features of such antennas.

Experiment on the shielding by hollow conducting tubes

This paper describes several practical aspects of shielding provided by openings such as ventilation vents acting as waveguides. Fundamental properties of electromagnetic waves in the interior of a hollow conducting cylindrical tube are presented. Then the guidelines for oscillators design and harmonic generation by nonlinearities are presented. A consequent wideband setup having low cost and common devices as well as high dynamic range is proposed to perform reliable measurements from 50 MHz to 1.5 GHz. Measurements of circular cylindrical waveguide effectiveness point out the simplicity of the systematic procedure and illustrate the effects of apertures on shielding walls. Shielding loss achieved by these apertures at frequencies below cutoff allows engineers to gain more insight into analysis and design of shields with intentional discontinuities used to exclude and to confine electromagnetic interference.

Dispersion characteristics of superimposed microstrip couplers

In the article by Mittra and Itoh (1971), an extremely elegant method for the determination of dispersion graphs of microstrip lines is given. We can show that with the help of certain minor modifications their calculations can be applied to superimposed couplers, providing excellent results which correspond well with those obtained experimentally.

Harmonic suppression in low pass filter designed by non uniform transmissions lines

The out band response of filters is of major importance because it mitigates interferences for adjacent applications. In this paper, a novel technique based on non uniform transmission lines (NUTLs) is used to suppress harmonics in the out band of a low pass microstrip filter. Explicit expressions describing accurately the behaviour of NUTLs are obtained from numerical resolution of Hills equation. Practical measurements showed good agreement with simulation results.

New Design of RFID TAG Using the Non Uniform Transmission Lines

The issue of our paper is to expose an original technique to improve the performance of RFID TAG in terms of its geometric dimensions and radiation pattern. This technique exploits the non uniform transmission lines (NUTLs) features to design the passive antenna element on the RFID TAG. We have yet demonstrated that geometric dimensions are reduced and the radiation pattern of the tag was improved by such use of NUTLs. Optimization of the profiles of the different elements of non uniform Lines achieves the appropriate radiation diagram and improves the radiation intensity, consequently.

A two dimensional magneto-inductive lens for near field imaging

In this paper, a planar near field magnetoinductive lens operating in the microwave range is presented. The proposed structure consists of two parallel planar arrays of metallic resonators, which are, once scaled in term of size as well as the array periodicity, the frequency of operation can be tuned over a wide frequency range. Thus the proposed design is potentially useful for many applications.

Subdiffraction resolution super lens based on negative refractive index transmission line metamaterial for free space imaging

In this paper, we propose a transmission line metamaterial super lens operating at 15.4 Ghz. The unit cell is built with a printed transmission line loaded with shunt inductor and series capacitor and it is designed to exhibit a negative refraction index equal -1. Such a microwave super lens can go beyond the diffraction limit and can be used for free space imaging.

Antenna backscattering and application to a cost effective non destructive testing method of carbon composites

A new method non destructive evaluation method of carbon composite was created based on a backscattering measurement. Results are satisfactory even without signal processing. Next research efforts will be directed to determination of minimal damage detection, sensitivity evaluation and signal processing scheme.