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RF power calibration up to 170 GHz

  • Metrology for Economy

PTB is the first national metrology institute (NMI) capable of calibrating sensors for measuring radio frequency power (RF power) up to a frequency of 170 GHz. This service was established in cooperation with national industry and in the European research project Opens external link in new windowTEMMT (2019 to 2022).


After several test and comparison measurements in 2020 and 2021, the first calibration for an industrial customer took place at the beginning of 2022, and the number of calibrations was increased to 13 by the end of 2023. Of these, four were calibrations for industry and nine were PTB-internal.

The measurement of the quantity RF power traceable to SI units (calibration) has been carried out at PTB for more than 50 years based on microcalorimeters. In other NMIs, other calorimetric measurement principles are used to some extent, but the majority use so-called twin microcalorimeters (schematics see Figure).

Unlike with other measurands, a microcalorimeter cannot be purchased commercially. The measuring set-ups of PTB are therefore all self-built. Presently PTB has six microcalorimeter measuring set-ups for up to 13 different configurations (coaxial connectors and waveguide interfaces) and, thus, covers the frequency range from a few MHz to 170 GHz without gaps.

In the past, only so-called thermistor sensors were considered as transfer standards. These have good metrological properties but also disadvantages (e.g., regarding measurement dynamic, speed, and ease of use) and are therefore no longer widely used in industry. For about ten years, thermoelectric sensors have consequently been used increasingly, and in the frequency range above 110 GHz there are no alternatives.

Sensor prototypes developed by a German manufacturer of measuring instruments are used at PTB for the calibrations in the 110 GHz to 170 GHz frequency range. Based on this traceability, however, all power meters with a standardized waveguide interface can in principle be measured. Eight of the 13 calibrations from PTB were performed on commercially available power meters, some of which had to be equipped with the required interface adapters, and five on prototype sensors. The latter are currently the only available transfer standards that can be calibrated directly in a microcalorimeter and therefore allow the lowest measurement uncertainty.



Twin microcalorimeter schematics 

Figure: Twin microcalorimeter schematics.



Opens internal link in current windowDepartment 2.2 “High Frequency and Electromagnetic Fields”


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