Some Techniques and Their Limitations as Related to the Measurement of Small Reflections in Precision Coaxial Transmission Lines

The techniques analyzed in this paper are based on precision-measuring systems that exhibit resolutions of 0.0001 in reflection coefficient and accuracies of 0.05 percent in characteristic impedance over the 100 MHz to 8.5 GHz frequency range. In order to consider safely reflection coefficients as high as 0.1, multiple reflections are not neglected in the analysis. Subjects considered include 1) the separation of measuring-system residual reflections utilizing air-line standards of specified, arbitrary, and variable length, 2) the limits of accuracy resulting from imperfect air-line standards and multiple reflections, 3) the importance of connector repeatability, and 4) the advantages realized through the use of highly stable impedance-matching tuners.