W-Band Internal Calibration Subsystem for Space Based Microwave Radiometers

An internal calibration subsystem operating in the W-band that is integrated in the frontend of a microwave radiometer has been developed: the calibration signals are generated by noise diodes and matched waveguide loads and coupled to the receiver by RF switches and directional couplers. The brightness temperatures of the injected calibration signals, calibration path losses, the isolation of the switches, as well as the transient behavior of the noise diodes and the switches have been determined using an accurate, temperature stabilized radiometric testbed. The testbed is described, and the measurement results are presented.