Origin of the Half-Wavelength Errors in Microwave Measurements Using Through-Line Calibrations

The through–line calibration family uses measurements of a through connection and an inserted line to determine the propagation constant of the line. This is typically used with measurements of a reflect standard to characterize fixturing errors. Subsequently, the S-parameters of a device under test are de-embedded. Measurement uncertainties occur at frequencies where the length of the line standard is an odd multiple of a half-wavelength. The origin of these errors is identified as fixture inconsistencies between the through and the line measurements. Error formulations are developed, and it is shown that a small fixturing error can be accounted for as a multiplicative transmission error. An error sensitivity function is developed and highlights the importance of fixture repeatability.