Measurement of vircator ultra-short solitary electromagnetic pulses MILOSLAV STEINBAUER, PETR DREXLER, PAVEL FIALA Department of Theoretical and Experimental Electrical Engineering Faculty of Electrical Engineering and Communication, Brno University of Technology Kolejní 4, 612 00 Brno CZECH REPUBLIC Abstract: In connection with the events of the last few years and with the increased number of terrorist activities, the problem of identification and measurement of electromagnetic weapons or other systems impact occurred. Among these are also microwave sources, which can reach extensive peak power of up to P max = 250 MW. Solitary, in some cases several times repeated, impulses lasting from t p ∈ <1, 60> ns, cause the destruction of semiconductor junctions. These days we can find scarcely no human activity, where semiconductor structures are not used. The problem of security support of the air traffic, transportation, computer nets, banks, national strategic data centers, and other applications crops up. Several types of system protection from the ultra-short electromagnetic pulses present itself, passive and active protection. The analysis of the possible measuring methods, convenient for the identification and measurement of the ultra- short solitary electromagnetic pulses is presented in this paper; some of the methods were chosen and used for practical measurement. Keywords: Ultra-short electromagnetic puls, high power microwave generator, calorimetric method, magneto-optical effect, multilayer sensor, vircator, semiconductors. 1 Methods Requirements imposed on the methods, available for capture and measurement of solitary impulses, are very rigorous. The common method applied to the measurement of the magnetic flux density respective power are not applicable for our purpose with regard to the expected impulse’s very short length and substantial power Fig. 1. Basic overview of the methods suitable to the purpose named is set out in works [1, 2, 3, 4, 5]. 1.1 Methods based on Faraday’s induction law One group of methods is based on the Faraday’s induction law application, where the impulse is located by sensor (coil with N s = 1÷50 turns). Signal induced in the coil is led to the recording device, generally an oscilloscope. Due to safety requirements, the distance between the sensor and the oscilloscope is l = 50 m. This parameter introduces a quality decrease of the recorded information in the way of the signal amplitude reduction, change of the signal phase and the impulse prolongation. Elimination of this limitation is in Version I, depicted in Fig. 2, made by backward correction exploiting the Laplace transformation. Impulses up to limit pulse length T max = 1 ns were measured by this method and magnetic flux φ was evaluated [6]. Version II exploits the possibility of principal elimination of the influence of the transmitting line between the sensor and the measuring device by an analogue U/f. converter. Available measuring devices can achieve measured impulses with the limit length T max = 5 ns. t (ns) 0 100 200 300 P (MW) 100 200 Pmax tp Figure 1. Typical course of short impulse instantaneous power The solution in Version III is similar to Version II, the difference is in the digital converter applied. By an available measuring devices application and fulfilled sampling theorem we can measure impulses with the limit length T max = 20 ns.