Characterization, calibration and macromodeling of RF current probes

Characterization of a current probe by measuring three port S-parameters with the probe clamped to a calibration fixture is presented. A simple calibration fixture based on a wire over ground plane is used. From the measured 3-port S-parameters, accurate de-embedding is performed to remove the fixture and transmission line effects to obtain the S-parameters of the current probe. Equivalent circuit representation of the fixture is utilized in the de-embedding procedure. Subsequently, vector fitting based macromodeling of the de-embedded S-parameters of the probe is performed. SPICE-compatible equivalent circuits are then obtained and their use in the simulation of physical tests with circuit simulators is demonstrated. Results for both commercial and simple in-house designed current probes are presented.