Direct comparison technique using a transfer power standard with an adapter and its uncertainty

The direct comparison technique using a transfer power standard with an adapter and its uncertainty are considered. A waveguide thermistor mount with an appropriate waveguide-to-coaxial adapter serves a new combined coaxial power standard. In order to obtain the effective efficiency of the combined standard, the phase as well as the magnitude of the adapter scattering parameters have to be known. Consequently, the adapter scattering parameters give rise to an additional uncertainty to the direct comparison technique. In this paper, a K-band waveguide thermistor mount with a WR42-2.4-mm adapter is used to calibrate a 2.4-mm coaxial power sensor. Measurement results are presented and its uncertainty is evaluated to be 2.5 % (k=2) in the frequency range of 18 GHz to 26.5 GHz.