Investigation Of A Nanosecond Pulse Generator

A nanosecond pulse generator requires light weight, small size, adjustable parameters and waveform of high stability when it's used for time-domain step response testing and pulse propagation researching. Considering the above requirements, a pulse generator which use the mercury wetted reed as the fast switch was presented, and the key factors affecting the waveform were also discussed in this paper. The main work carried out as follows:The principle in which transmission line generates high-voltage pulse was analyzed theoretically from the view point of electromagnetic wave transmission and its equivalent circuit. The characteristics of LCR circuit output pulse were analyzed using the mathematical method. The Software PSpice was used to discuss the influence of the distributed parameters. The results showed that the charging circuit and load distributed parameters make the pulse steepness slow and lead to overshoot both at the front and back edges. The switch distributed parameters make a damped oscillation on the top and tail of the pulse. Oscillation cycle and damping factor have a corresponding relation with the distributed parameters.The feasibility analysis of adjustable pulsed-width technology with ferroelectric/ferrite material was presented in the paper. Experiments were carried out to study whether Ferrite material could be applied to the pulse generator. Results show that the introduction of ferrite materials makes pulse risetime changing from 0.4ns to 1.4ns, but the pulse falltime don't change significantly, because the influence of the additional transmission line can't be removed. The experimental datas provide a valuable reference for the following improvement.The design principle of mercury wetted reed and the equivalent circuit model were studied in detail. The results indicate that the internal structural discontinuity is the main reason for the existence of the distributed parameters. For the further analysis of the oscillation, circuit analysis and numerical calculation were both applied to analyze the switch equivalent circuit. The results showed that the oscillation is mainly caused by the distributed inductance, distributed capacitance and arc resistance of the switch contact, and that distributed capacitance of about 4.7nH, the distributed inductance of 2.8pF, pulse risetime of about 0.2ns, damping oscillation cycle of 0.7ns, oscillation frequency of 1.4GHz. Tests of PFL with different lengths and different charging voltage reveal the existence of damped oscillation wave, which confirms the conclusion of theory analysis and numerical calculation very well.The prototypical assembly and parameters design of the pulse generator have been completed. The pulse generator has light weight and compact structure. The pulse measuring system that consists of attenuators and high-speed oscilloscope was also designed and calibrated in our work, which demonstrates excellent performance for nanosecond pulse measuring. A ultra-wideband absorping filter for pulse-shaping was also designed and tested. The experimental results show that the filter can meet the design requirements.The improved pulse generator tests show that when the charging voltage is 1.4kV, the pulse generator can produces a double-exponential pulse with 0.6ns falltime, the amplitude exceeds 0.6kV, and the pulse width and amplitude can be adjusted by changing the circuit parameters. Experiments were carried out to assess stability of the waveforms. The results showe that the pulse amplitudes has the relative standard deviation of less than 2%, the pulse width and the falltime have the relative standard deviation of less than 1%. The report proved that the generator has good stability for practical applications.