A Comparison Of Measurement Uncertainty In Vector Network Analyzers And Time Domain Reflectometers

By W.L. Gore & Associates

Abstract:
Measurement uncertainty has a direct impact on the reliability of test instruments. To determine if there is a quantifiable difference in measurement uncertainty between the TDR and VNA, W. L. Gore & Associates performed a series of experiments, initially testing six cable assemblies in controlled conditions on each instrument. The instruments' measurement uncertain under best-case scenario was evaulated using the highest-performing assembly. To ensure TDR/VNA test parity, the VNA's performance was evaluated using a s11 one-port reflection method as well as the more traditional s21 two-port transmission method.

Introduction

In the test and measurement industry, two distinct camps exist: those who favor vector network analyzers (VNA) and those who favor time domain reflectometers (TDR). Each camp relies heavily upon its instrument of choice for a variety of test and measurement and analytical tasks. The TDR's strong suit is temporal analysis — characterizing impedance or refl ection coefficient with respect to time. Its quick setup, intuitive controls, and results-oriented operation appeal to a broad range of users. The VNA excels in frequency domain analysis — characterizing amplitude and phase with respect to frequency. Learning to operate the VNA can be intimidating, but in return it offers an extremely stable, precise, and versatile measurement platform. Interestingly, both instruments have the ability to perform time or frequency domain analysis through built-in Fast Fourier Transform (FFT) algorithms or ancillary software.