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HF power

Working Group 2.22

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Traceability to SI of the measurand HF power is established by substitution of d.c. power in a bolometer element which is placed in a coaxial or waveguide power sensor. Indicator of the equality of HF power and d.c. power is the same degree of heating of the bolometer element which is operated as temperature sensitive resistor located in one branch of a Wheatstone bridge. The fraction of HF power that is absorbed outside the bolometer element and thus not detected by the substitution measurement can be accurately determined by means of a microcalorimeter by measuring the temperature difference at the input connector of the sensor for the switchung states HF power on and off. This calorimetric measurement principle can be also applied to thermoelectric power sensors, that do not contain active electronic circuitry. Here, the HF power is substituted in the sensor by a low-frequency or d.c. power resulting in the same power indication at the sensor output. As in the case of bolometer sensors, the effective efficiency is determined by measuring the temperature rise at the input connector of the sensor when HF power is switched on. Knowing the input reflection coefficient of the power sensor, the calibration factor as ratio of substituted d.c. power to incident HF power to the power sensor can be calculated from the effective efficiency.

 

WR-10 waveguide calorimeter for the frequency range 75 GHz - 110 GHz

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Research/Development

The department operates microcalorimeter setups for both coaxial and waveguide transmission line systems for the automated determination of effective efficiency and calibration factor of power transfer standards up to 110 GHz. Additional HF power measuring setups beyond 110 GHz are currently under development. This includes the development of novel transfer standards and microcalorimeters.

Furthermore, direct comparison setups are operated up to 50 GHz for the determination of the calibration factor of power sensors in different connector systems. The direct comparison measurement capabilites are currently extended up to 110 GHz.

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