Coaxial Termination Load for High-Voltage Fast Transient Pulse Measurement

A high-voltage fast transient pulse termination load using a 10-mm distributed ceramic-carbon-rod resistor has been developed. It is capable of measuring a pulse´s voltage amplitudes up to 100 kV and a rise time less than 300 ps. A difficulty for the development of the high-voltage ultrawideband (UWB) termination device is the compromise of the resistive element size considering opposite characteristics of the high voltage and the wideband frequency. A smaller resistor shows the better high-frequency performance but the worse high-voltage insulation characteristic. Many previous studies in the area of pulsed-power development have used a nonscaled load device for the pulse termination; nevertheless, a mismatch between a source and a load impedance results in significant misunderstanding of the output voltage in a high-voltage fast transient pulse measurement. In this paper, we propose a newly developed high-voltage UWB coaxial load improving impedance characteristics of a nonscaled load device. Physical length of a rod resistor is far longer than a wavelength of an input pulse so that the impedance linearly increases in the moving direction of the incoming pulse. The proposed log-scaled coaxial load device with a distributed ceramic-carbon-rod resistor has a property of compensating impedance variations, which is caused by the usage of an electrically long rod resistor, by means of diminishing coaxial characteristic impedance exponentially along the resistor. This diminishing coaxial structure makes it possible to maintain consistent impedance through the entire load device. Experimental results show good agreement with expectations in aspects of the voltage standing-wave ratio under 1.25 : 1 from dc to 10 GHz; peak impedance variations under 10% with the final converged impedance of 54.86 Ω; and negligible reflections when injecting the repetitive pulsed input with amplitudes from 15 to 100 kV, a rise time below 300 ps, and repetition rates under 10 kHz.