Joël Andrieu

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

High Pulsed Power Sources for Broadband Radiation

This paper explains the design and production of two autonomous ultrawideband (UWB) radiation sources. These sources consist of a high-gain broadband antenna that is driven by one of two subnanosecond pulsed power sources. Each source is made up of a Marx generator and a pulse-forming device based on the use of a gaseous spark gap. The first source combines a four-stage 200-kV/34-J Marx generator with a coaxial pulse-forming line. Its main characteristics are an output voltage of 100 kV, a 250-ps rise time, a subnanosecond pulse duration, and a repetition rate of about 40 Hz. The second pulsed source is a ten-stage subnanosecond Marx generator that delivers pulses in the 250-kV/1.5-J range, with a 300-ps rise time and a subnanosecond pulse duration at a pulse repetition rate of 350 Hz. Probes were produced based on capacitive line dividers to measure both the temporal characteristics and the high-voltage (HV) amplitude of the pulses delivered by the pulsed power sources. The antenna, combined with these two pulsed sources, is a traveling-wave antenna called the Valentine antenna. Some mechanical modifications were made to the antenna to improve its dielectric strength. First, a 3-D model of the antenna was created on time-domain electromagnetic software to study the influence of these modifications on its main radiating characteristics. Its high gain and its capability to radiate short pulses without dispersion allow us to achieve a high measured figure of merit (the maximum value of far-field peak-to-peak electric field strength multiplied by the distance). A new method called the Instantaneous Electromagnetic Field Measurement by Signature of a Neutral Object (MICHELSON) method is used to measure the very intense electromagnetic fields that are radiated. The incident field is diffracted by a special small-dimension target. The diffracted field is measured by a conventional low-power UWB antenna. The target that is used has small dimensions, and no cables are used in the field region; thus, the electromagnetic interference that is generated and undergone by the measurement device is considerably limited. The figure of merit that is measured is 436 kV.

Land mine detection with an ultra-wideband SAR system

PULSAR is an Ultra Wide Band (UWB) short pulse Radar developed by the CELAR (French Technical Center for Armament Electronics) and the IRCOM (Research Institute of Microwave and Optical Communications) in order to detect foliage and ground concealed mines. An instrumentation measurement system has been designed and implemented, in particular new 2D broad band antennas with a very low pulse distortion. The clutter suppression is based on background subtraction and wavelet transforms. These data are used to obtain SAR ultra wide band images by transient methods. The following discussion describes the device, the experimental results and the signal processing currently utilized. Future development efforts on this system (generator, acquisition means .) are detailed. At the same time a theoretical study is made to estimate target transient responses captured by the system. So a FDTD code is modified to simulate buried objects detection by the radar.

A Novel Antenna for Transient Applications in the Frequency Band 300 MHz – 3 GHz: The Valentine Antenna

We propose a novel ultrawideband (UWB) antenna designed specially for transient UWB radar applications. This work is a part of a new project concerning an optoelectronic UWB radar demonstrator with an array of four antennas. This project required the development of a new UWB antenna: the Valentine antenna. This antenna must be lighter and more compact in H-plane to allow the assembly of the array. This array must have a volume lower than 1 m3. This antenna, which is composed of curved metallic strips, radiates ultrashort pulses in the frequency band 300 MHz - 3 GHz with very low dispersion, a high gain and a low cross-polarization in the axial direction. The Valentine antenna must support 10kV of peak voltage. This paper describes the Valentine antenna and its main radiation characteristics

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.

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.

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.

Utilization of Target Scattering to Measure High-Level Electromagnetic Fields: The MICHELSON Method

The intention of this paper is to present the instantaneous electromagnetic field measurement by signature of a neutral object (MICHELSON) method. The MICHELSON method is relatively new and enables the measurement of high-level electromagnetic fields from the utilization of a target. The incident field scattering on the target allows us to move the field measurement to a new location where the scattered field can then be measured using simple equipment and without breakdown risk. This method does away with the necessity for cables in the test zone. When using small targets, the induced disturbances in the incident field are limited. The MICHELSON method is implemented to characterize high-level electromagnetic sources whereby the signals radiated can be harmonic signals as well as transient pulses.

A 250KV-300PS-350HZ Marx generator as source for an UWB radiation system

This paper aims at presenting the design and realisation of an autonomous, ultra wideband (UWB) radiation source consisting of a high gain broadband antenna driven by a subnanosecond pulsed power source.

Optoelectronic ultra-wide band radar system: RUGBI

We propose an ultra wide band radar system based on a coherent emission of an ultra-wide band antenna array using photoconductive switching devices. The triggering process is obtained by excitation of semiconductor samples in linear mode using a picosecond laser source. The emitting antenna system and the receiving antenna developed by our research laboratory, present some specific qualities suitable for radiation and measurement of ultra-short pulses