A coaxial calorimeter and its use as a reference standard in an automated microwave power calibration system

The construction of a dc-substitution coaxial calorimeter having 7-mm-diameter input line is described and an evaluation of its uncertainty is presented. An automated procedure is then outlined for calibrating a power transfer standard against the calorimeter. The transfer standard consists of a directional coupler with a thermistor mount on its side arm. The power transfer standard can in turn be used for automated calibration of thermistor mounts and other power sensors. The overall estimated uncertainty (expressed as one standard deviation) of the measurement of the effective efficiency of a thermistor mount varies from 0.2 percent at 2 GHz to 0.4 percent at 18 GHz.