Stéphane Vauchamp

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.

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.

Impulse optoelectronic Ultra-Wide Band antenna array

The laboratory XLIM has developed an impulse optoelectronic ultra-wide band antenna array for UWB radar applications. This paper presents this system in which photoconductive switches generating high voltage monopolar pulses and UWB antennas are associated. The control of the releasing delay of the sources via optic provides to sum the radiation power and to steer the transient radiation beam accurately. The experiments realized with this optoelectronic array validate these two concepts. We also propose another way of improvement of these systems by using bipolar pulse generators.