Performances of an ultra compact, high-power, monocycle pulse former for WB and UWB applications

Abstract

This paper presents the design and the performances of an ultra compact, general-purpose, and high-power ultrawide band (UWB) source named GIMLI. The system was developed for dual use, from laboratory to battlefield applications. The power supply is a dedicated coaxial Marx generator composed of specifically designed stages. In an 11 stages configuration, the rise time can be less than 15 ns (measured on a 50 Ω load) with an operating voltage reaching values up to 500 kV (with an open circuit configuration). An ultra compact (less than 2 liters) pulse forming stage (PFS) is directly connected to the output of the Marx generator. It is composed of a pulse sharpening assembly made up of a peaking and a multi channel grounding spark gap, running under a high pressure of nitrogen. These switches are followed by a monopulse-to-monocycle converter module, which is based on a Blumlein coaxial line. The bipolar signal at the output of the PFS has a total duration which can be adjusted from 1 to a few ns by the use of different lengths of the Blumlein module. For example, the smallest device generates a signal composed of two Gaussian pulses. A positive one is followed by a negative one and the two are separated by less than 500 ps peak to peak with rise times lower than 250 ps. Measured on a 50 Ω dedicated ultra wideband resistive load, the peak-to-peak output voltage is tunable up to 400 kV. With a right adjustment (in pressure and in distances inside the electrodes chamber) the maximum dV/dt can reach 2.1015 V/s. If a more important slope is required, it is possible to insert a pre-peaking stage between the Marx generator and the PFS. Using this stage allows to get performances in the order of 5.1015 V/s (rise times lower than 150 ps). The use of a coaxial 50 Ω output enables to connect the GIMLI source to many different types of antennas, allowing the radiation of WB or UWB electromagnetic signals. For instance, high-power radiation tests were performed with the pulser connected to a specific half TEM ridged horn. The results showed that the electrical field acquired at 10 m was higher than 150 kV/m peak to peak.