Michèle Lalande

AN ULTRA WIDEBAND IMPULSE OPTOELECTRONIC RADAR: RUGBI

An ultra wideband radar system based on a coherent emission of an ultra-wideband antenna array using photoconductive switching devices is proposed. The triggering process is obtained by the excitation of semiconductor samples in linear mode using a picosecond laser source. The emitting antenna system and the receiving antenna developed by the Research Institute XLIM present some specific qualities suitable for radiation and measurement of ultrashort pulses. The optical control of the sources allows to sum the

A Transient UWB Antenna Array Used with Complex Impedance Surfaces

The conception of a novel Ultra-Wideband (UWB) antenna array, designed especially for transient radar applications through the frequency band (300 MHz-3 GHz), is proposed in this paper. For these applications, the elementary antenna must be compact and nondispersive, and the array must be able to steer in two dimensions. The geometry of the elementary antenna and its radiation characteristics are presented. The array beam steering is analyzed and a technique making the increase of the transient front-to-back ratio possible is described.

Metamaterial-Based Highly Directive Antenna: Application in a Monochromatic Wave Radar for a Contactless Measurement of the Breathing Activity

We report the numerical and experimental investigation of a highly directive Fabry-Perot (FP) cavity antenna based on a metamaterial, operating in the microwave regime. Numerical simulations using flnite element method and re∞ection-transmission microwave measurements have been performed and a good quantitative agreement has been observed. Measured return losses and radiations patterns done in an anechoic chamber agree very well with the simulated ones. The potential application of the proposed FP cavity antenna in a non-contact breathing sensor is proposed and evaluated. Experimental record and frequency spectrum for respiratory movements of human-being (voluntary under test) are presented. The low cost and simple fabrication process of the proposed FP cavity antenna make it very promising for its integration in modern telecommunication systems.

Equivalent Model of Photoswitch: Application to the UWB Antenna Design Integrating Impulse Feeding

Optoelectronic devices triggered by a laser ∞ash and operating in linear switching regime allow the generation of short pulses with small time jitters (2ps typically). An Ultra Wide Band antenna array combining as many of this photoswitches as antennas has the advantage to increase the radiation power on one hand and to ofier the agility of the radiation beam on the other hand obtained by time delay of laser illumination. During the step of antenna design, it becomes important to take into account the photoswitch integration in order to increase the peak power and the frequency band of the generated output signal. This paper presents an equivalent model of photoswitch obtained with the transient solver of CST Microwave Studio coupled within CST Design Studio. The second part of this article is dedicated to the integration of a photoswitch even within the antenna.

High-Voltage Rectifier Diodes Used as Photoconductive Device for Microwave Pulse Generation

Generation of unipolar and bipolar pulses by using high- and medium-voltage silicon rectifier diodes is achieved. These components are provided by the French Atomic Energy Commission (CEA). Furthermore, these devices work in the linear mode of photoconducting switches. Generation of electrical unipolar pulses with an amplitude of 10.7 kV and a full-width at half-maximum of 300 ps by using only 1.2 mJ of optical power is demonstrated. This energy value is 10-100 times less than usually published during the past decades. Furthermore, the linear mode running of these devices permits to synchronize several generators with a precision as low as 2 ps. This low timing jitter is useful for bipolar generators in order to control their spectrum with high precision, i.e., bipolar pulses of 3 kV peak-to-peak have been generated with a cycle duration of 400 ps and an optical energy of 1 mJ

Size reduction and radiation optimization on UWB antenna

This paper deals with miniaturization techniques and radiating optimization on UWB antenna in order to make an antenna array. The hard point with size reduction of an antenna is the back radiation, the cross polarization and the antenna adaptation. Several methods to keep the antenna adapted to our bandwidth [300 MHz - 3 GHz] are studied. A detailed study of the travelling wave elementary antenna is proposed. Some techniques are applied to reduce back radiation and cross polarization by the use of slots in order to reduce back radiation and resistive loads in order to reduce surface current levels and side cross polarization.

AN INNOVATIVE RADAR IMAGING SYSTEM BASED ON THE CAPABILITY OF AN UWB ARRAY TO STEER SUCCESSIVELY IN DIFFERENT DIRECTIONS

An innovative radar imaging system, based on the capability of a flxed UWB array to radiate short pulses in difierent directions along time with the principle of electronic beam steering, is presented in this paper. To demonstrate its concept, the analysis presented in this paper is based on simulation results. As function of the use of either only one antenna or several antennas in reception, two radar imaging algorithms have been developed and are detailed in this paper. These algorithms permit to obtain an image of the analyzed scene thanks to the transient beam pattern of the array used in emission. Finally, with a same analyzed scene, these algorithms have been compared with the time reversal method and the back projection algorithm, in association with a SAR imaging system. The conditions of applicability of these methods are also discussed.

Electromagnetic analysis of exponentially tapered coplanar stripline antennas used in coherent microwave transient spectroscopy technique

This paper deals with an electromagnetic analysis by FDTD method of exponentially tapered coplanar stripline (ETCS) antennas used for the material characterisation by spectroscopy technique. This analysis leads to the time and harmonic evolution of radiated fled at every point in the space. The effect of substrate thickness on radiation properties of ETCS antennas, radiation patterns are presented. The received signal is calculated and compared to the experimental signal.

Static study for the analysis of ultra-short pulse propagation on complex planar structures

In this paper, a static electromagnetic study of planar structures is effected. The determination of electric and magnetic field distributions is used to deduce the characteristic impedance of these structures. The second application concerns the simulation of the line feed when a transient analysis using the finite difference time domain method is used to analyse the line behaviour. In the case of a microstrip line, this new excitation method is compared to two excitations which are generally used. >

Ultra-Wideband Electrical Pulse Generator Using Photoconductive Semiconductor Switches

We achieved the generation of unipolar and bipolar ultra-wideband electrical pulses by using a photoconductive device. It relies on a doped silicon substrate which is used in the linear mode with less optical energy than usually published. This running mode allows the synchronisation of several sources with a timing jitter less than 5 ps. However it permits to control the low frequency components of the bipolar generator by means of the synchronisation of two photoconductors. So we generated unipolar pulses from 43 ps to 300 ps of duration (full width at half maximum: FWHM) with peak voltage up to 10700 V and bipolar pulses between 200 ps and 450 ps of cycle length with 3000 V of peak voltage.