Improved Evaluation of Planar Calibration Standards Using the TDR Preselection Method

Abstract

Calibration and correction methods for the Vector Network Analyzer (VNA) are based on the fundamental assumption of the constant error model, which is independent of connected calibration standards and/or devices under test (DUT). Unfortunately, this assumption is not satisfied well for planar calibration standards fabricated by etching technology on soft substrates. An evaluation of the error model is affected especially by variations in the manufacturing process and also by the reproducibility of an assembly. In this paper, we propose error minimization by selecting the best combination of available calibration standards based on time domain reflection (TDR) measurement, which can also be obtained by the fourier transformation from the measured S-parameters. The proposed method was verified experimentally using short, open, load and thru (SOLT) standards fabricated on an FR4 laminate substrate which achieves the essential reduction of the measurement error in the frequency range up to 15 GHz.