High pulsed power sources for broadband radiation

Abstract : 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.