Modelling the effect of port recession on VNA one-port calibrations

Considerable attention has been devoted to the effect of recessed connections on the accuracy of vector network analyser (VNA) calibrations. Recession, defined as the gap between connectors, produces a discontinuity in the transmission line, which can be modelled as a short section of line with a different characteristic impedance. The parameters which define this discontinuity are the diameter and length of the intermediate section. The diameter is that of the male connector pin and the length is a function of the recession and/or protrusion of both connectors. Together with the diameter of the outer conductor, these parameters allow the calculation of the characteristic impedance of the section and the reflection coefficient of the termination. Simulations of the performance of a mismatch airline are presented in order to assess the correctness of our model. Subsequently, the same model is applied to the open-short-sliding load calibration of a vector network analyser. We show that the effects of recession during calibration and/or measurement can be predicted with the aid of computer simulations.