Improvements to the microwave mixer and power sensor linearity measurement capability at the National Physical Laboratory

Knowledge of the performance of power sensors and mixers is vital to the uncertainty analysis of the RF and microwave attenuation calibration systems held at the National Physical Laboratory (NPL). Recently the facilities used to characterise these components have been improved with the aim of measuring the response to ±0.0003 dB over a 40 dB range from 10 MHz to 60 GHz. The principal changes to the original linearity measurement systems have been the selection of the highly repeatable attenuator, used to generate a step change in the RF signal, and the way in which the detector in the mixer measurement system is operated. Measurements on these systems have been used to re-assess the National Attenuation system capabilities and to select the optimal operating conditions for the mixers and power sensors used in them.