Calibration of current transducers at high frequencies

The transfer impedances of current transducers are estimated using a special calibration fixture, which is often assumed to be perfectly matched at its coaxial ports. However, the errors inherent in this approximation increase with frequency, making the measurement of cable currents increasingly inaccurate at higher frequencies. A one-dimensional (1-D) transmission line model is proposed to account for such errors in a calibration fixture of simple design by using additional measurements to quantify the mismatches in the system. This technique is validated using a numerical model of such a calibration fixture as well against experimental data and numerical predictions for the current induced on a wire inside a rectangular cavity due to an external source that is coupled into the interior via an aperture. It is concluded that the proposed approach provides improved results with a calibration fixture of simple design for frequencies up to at least 600 MHz.