Receiver as a radiometer calibration target

What is proposed in this paper as a new, novel idea is to use the input port of a complete radiometer receiver as a calibration target instead of a dedicated Active Cold Load (ACL). What is also proposed is to use the input port as a phase calibration target as well. Modern LNA technology has made very low noise figures and return losses possible; both key parameters for a cold and stable ACL. Low noise figure and good matching combined with a typical high isolation of an amplifier makes it possible to use a receiver itself as a cold calibration target. This is beneficial in instruments inherently having (at least) two receivers (pushbroom or polarimetric radiometer for example).