Power Standards
The function of the Power Section is to research, develop and disseminate standards of microwave power. The work is directed at supplying traceability to UKAS and other-accredited laboratories.
Present capabilities include:
Calibration systems based on microcalorimetry are capable of measuring - in a manner traceable to fundamental national standards - the efficiency (power indicated/power delivered) or calibration factor (power indicated/power incident) of barretter or thermistor power sensors. Standards are currently available in waveguide sizes 16, 18, 20, 22, 23, 25 and 27 with a measurement uncertainty ranging from 0.2 % at the lower frequencies to 2.5 % at the higher frequencies for a 95 % confidence level.
Transfer systems are based on waveguide multistate reflectometers whose purpose is to enable the estimation of efficiencies (or calibration factors) of power sensors, which need not be of the barretter or thermistor type, to be made. The estimation is performed by comparing the power indicated by the sensor and that indicated by a sensor calibrated by microcalorimetry. Multistate systems are available in the waveguide sizes mentioned above.
Coaxial measuring systems operating between DC and 26.5 GHz, in which sensors are calibrated directly against coaxial power standards, are also available. By using waveguide systems in conjunction with an accurately characterised set of coaxial to waveguide transformers coaxial sensors up to 50 GHz can be calibrated. Coaxial sensors operating below 8.2 GHz are calibrated by NPL using a 14 mm twin load calorimeter.
Current development projects include:
- Frequency extension of a twin load 3.5 mm coaxial calorimeter aimed at enabling the direct calibration of power sensors from DC to 33 GHz.
- A twin load 2.4 mm calorimeter aimed at enabling the direct calibration of 2.4 mm power sensors from DC to 50 GHz.
- A medium power system providing traceable measurement at 1 to 10 W from 10 MHz to 18 GHz.
- Power measurements to support the wireless communications industry.
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