Coaxial Twin-Loaded Microwave Power Calorimeters
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Application
Dual line, or dry load coaxial calorimeters, and the associated transfer systems are the best way to deliver world leading measurements of the RF and Microwave power. The calorimeter is normally used in conjunction with a transfer standard (typically a power splitter and highly stable power detector) to calibrate commercial power sensors. The calorimeter, being thermal in operation, is relatively slow in operation and is normally only used to directly characterise the power transfer instrument. The transfer standard is then used to calibrate other power sensors.
The traceability of the RF power measurement is through DC voltage and resistance. These parameters being derived ultimately from the primary quantum voltage (Josephson Junction) and resistance (Quantum Hall) standards held by many leading National Measurement Institutes.
Frequency Coverage
NPL has built calorimeters in several coaxial line sizes, most recently in the popular 7 and 3.5 mm lines. These operate over the frequency ranges 100 kHz to 18 GHz and 10 MHz and 26.5 GHz respectively. The design can be adapted to operate up to 50 GHz using the 2.4 mm line.
Dynamic range
Our systems operate over a typical power range of 0.5 to 25 mW, matching the power levels required by standards laboratories.
Associated Equipment
NPL is able to deliver not just a calorimeter, but a complete power measurement capability. This would include a calorimeter, transfer standard, microwave source, DC voltage and resistance standards, measurement and analysis software and a control computer. Documentation including operating procedures are available and training in the system use can be delivered, either at NPL or at the user’s laboratory.
Supported devices
The software and hardware will support the majority of commercial power sensors and meters employed in standards, calibration and testing laboratories. Our systems are regularly being developed to support the latest generation of power sensors, many of which now include internal electronic frequency correction.
Related Power Standards
For waveguide applications, in particular at millimetre wavelength, we can supply waveguide micro-calorimeters and transfer systems.
Uncertainties
The calorimeter systems, being developed from our own standards, offer the user comparable measurement uncertainties to that available from NPL’s measurement service. Our capabilities have been verified and accredited by the United Kingdom Accreditation Service (UKAS) and our capability can be found on their website and also on the BIPM Calibration and Measurement Capability database.
