A pulsed GTEM system for UHF sensor calibration

A system for measuring the sensitivity of electric field sensors at UHF usi ng a novel gigahertz transverse electromagnetic (GTEM) cell is described. T he system was developed to enable calibration of UHF couplers that are used to detect insulation defects in gas insulated substations, The frequency r esponse of a sensor is determined using fast Fourier transform (FFT) proces sing of its output voltage when it is subjected to a step electric field wi th a rise time of less than 300 ps, Provided the step response of the senso r is relatively short, the absorbing termination of the GTEM cell can be di spensed with, simplifying its construction The need for impedance matching at the cell input can be eliminated by using a signal source that absorbs t he reflected energy, In addition, the use of a wire septum offers the poten tial for improving field uniformity. A description of the measurement syste m is given, and some typical results are presented.