Wide-band characterization of current probes

The use of current probes for the injection of wide-band disturbance in electromagnetic compatibility applications requires their accurate characterization up to few gigahertz. While the representation of the current probe with a simple transformer is acceptable at low frequencies, the spectral content of fast signals requires models which are accurate even at gigahertz frequencies. This can be accomplished directly by measurements in the frequency domain (FD), making use of a S-matrix representation of the probe, or in the time domain (TD), recovering the transfer functions from the impulse responses measurement. Both techniques suffer limitations due to numerical and experimental problems; in particular, the FD approach leads to the solution of an inverse problem, with numerical instabilities in the high-frequency range, whereas the TD approach is not so accurate in the low-frequency range of the sought transfer function. The paper combines the two techniques to overcome these difficulties and achieve a better accuracy across the overall bandwidth. The characterization of a commercially available current probe allows comparison of numerical results with experimental measurements.