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Abstract

Disclosed are the following three improvements to apparatus employing a microwave radiometer to measure the temperature of a specimen: By situating a low-loss, high-temperature dielectric microwave antenna, which may be composed of low-loss alumina ceramic, within a high-loss-high-temperature antenna sheath, which may be a ceramic composed of an alumina-graphite mixture, a microwave radiometer may be employed to continuously measure the temperature of a material at high temperature, such as molten steel. A Dicke switch replacement for a microwave radiometer comprises a first hybrid ring in which (1) a first combination of first and second input signals thereto derived at a first output port thereof is amplified and forwarded through a switchable phase shifter to a first input port of a second hybrid ring, and (2) a second combination of the first and second input signals thereto derived at a second output port thereof is amplified and forwarded directly to a second input port of the second hybrid ring, resulting in one of the amplified first and second input signals being derived at a first output port of the second hybrid ring and the other of the amplified first and second input signals being derived at a second output port of the second hybrid ring. Switching the switchable phase shifter back-and-forth between 0.degree. and 180.degree. phase shift cyclically reverses the respective output ports of the second hybrid ring at which each of the amplified first and second input signals is derived. A resistance, terminating a coaxial transmission line that couples it to the input of a microwave radiometer, is heated by a heater surrounding it that is energized by an amount of current controlled by the radiometer output. The control is such that the temperature of the resistance reaches a steady state at which it matches the temperature of the specimen. A thermocouple probe in thermal contact with the resistance permits the temperature of the resistance to be indicated by a thermocouple meter.

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