To measure temperature in an electromagnetic field a thermocouple is connected to a meter. The temperature to be measured is sensed and converted into a D.C. voltage by the thermocouple. This D.C. voltage causes the meter to indicate the temperature. To prevent error due to electromagnetically coupled energy heating the thermocouple and/or producing a high frequency current which is conducted to the meter circuit from interfering with the meter readings, a physically small thermocouple with semiconductor leads or a semiconductor thermocouple having semiconductor leads is provided.
A microwave active noise source and method used for calibrating a radiometer includes a transistor configured as a noise equivalent model having a gate port, drain port and source port. During calibration of the radiometer the drain port is terminated and a bias circuit applies DC bias to the noise equivalent model. The bias circuit controls the DC bias such that a hot thermal radiation temperature and a cold thermal radiation temperature are alternately generated at the gate port of the noise equivalent model. A source inductance coupled to the source port of the noise equivalent model provides series feedback. To match the impedances in the noise source, an output matching impedance network is connected to the drain port and an input matching impedance network is connected to the gate port of the noise equivalent model. The input matching impedance network includes an input port for outputting the hot and cold thermal radiation temperatures used to calibrate the radiometer.
Apparatus and a method for radiometric temperature measurement comprises a radiometer receiver coupled to an antenna/calibration switch that has coupled thereto a brightness temperature signal. A driver coupled to the antenna/calibration switch controls the operation of the switch between an antenna mode and a calibration mode. An adjustable cold/warm noise source is coupled to the antenna/calibration switch to provide a calibration radiation temperature applied through the antenna/calibration switch in the calibration mode to the radiometer receiver. An output of the radiometer receiver is coupled to the adjustable cold/warm noise source and is adjusted in accordance with the output of the radiometer receiver for a null comparison measurement. Also coupled between the output of the radiometer receiver and the antenna/calibration switch is a mode selector switch that operates to a mode one position to couple the output of the radiometer receiver to the adjustable cold/warm noise source. A bias source is also coupled to the mode selector switch and actuation of the mode selector switch into a mode two position couples the bias source to the adjustable cold/warm noise source.
