Determination of the correction factor of a waveguide microcalorimeter

A novel, self-consistent approach for the determination of the correction factor of a waveguide microcalorimeter is described. The method is based on the measurement of offset shorts of different length followed by one single calibration measurement of an unknown thermistor DUT. Without precisely measuring the RF power incident to the reference plane, both calibration factor of the DUT as well as the calorimeter correction factor are determined. The method theoretically takes into account the different surface current distributions and associated waveguide losses being existent for the offset short as well as for the DUT measurements. It has been applied to a recently developed PTB twin-type microcalorimeter (33-50 GHz) resulting in low uncertainties of the effective efficiency of thermistor power sensors.