Errors and uncertainties in microwave measurements (introductory lecture)

An account is given of the major systematic errors likely to occur in microwave measurements of impedance (or equivalent parameter), power level, attenuation and noise factor. In particular, uncertainties arising from imperfections in the measuring apparatus, which act in conjunction with uncontrolled variables in the apparatus under test, are discussed. Such uncertainties in power level, attenuation and noise factor occur because the definitions are chosen to reduce the number of subsidiary measurements to a minimum. The paper opens with a brief statement of the requirements for fundamental measurement and of how far they can be met in microwave measurements. This is followed by an account of how various known methods of detecting and eliminating systematic errors can be applied. The conclusions point out that the practical need to keep subsidiary impedance measurements to a minimum calls for better values of voltage standing-wave ratio in measuring instruments than those tolerated hitherto, particularly in apparatus with coaxial connectors.