Analysis and modification for RF low frequency leakage of the type-N coaxial thermistor sensor

This paper analyzes previous measurements of the effective efficiency of type-N coaxial thermistor sensors from 10 MHz to 18 GHz in Radio frequency (RF) power standard of international comparison. A dramatical decrease of effective efficiency is found at lower frequencies, leading to high measurement uncertainty. RF leakage is observed during calibration of the type-N coaxial thermistor sensor. The working state of the power meter is affected by the leaked RF signal, yielding lower calibration factor in previous results. In this paper, a filter circuit is designed to block the leakage of RF signals. Results with filter applied are proved by the manual open-loop method and the transfer standard (TS) calibrations.