A calibration system for microwave radiometers based on a modulator–calibrator

A system for automatic internal calibration of millimeter-range radiometers is described. This system is based on an electrically controlled modulator–calibrator, which is a compact solid-state device that combines the functions of a modulator and a source of stable noise calibration signals. Stability of the calibration levels is provided by thermostatting the modulator–calibrator case and stabilization of the control currents. The calibration and data-collection process is governed by software using a special digital module and a personal computer.