Uncertainty of Radiometer Calibration Loads and Its Impact on Radiometric Measurements

We present an uncertainty analysis of radiometer calibration. The procedure can be used to determine the uncertainty in the nominal brightness temperature of the unknown scene. A total power radiometer requires frequent calibration with known reference loads that are connected to the radiometer. Our analysis includes uncertainties from the radiometer calibration loads and from the connecting network (CN) that is required to multiplex calibration loads and scene to the radiometer input. We show the design and analysis of three calibration loads and how their uncertainties propagate from load terminals to the radiometer calibration plane and to the scene. All three loads, including a cryogenic load, are simple, inexpensive, and show great stability and accuracy. We give an uncertainty calculation example for our three calibration loads and for the CN. We validate our model and the long-term stability of the loads through measurements. The analysis is done at 52 GHz, but the analysis and the construction of the loads are generic and easily scalable to other frequencies.