Variability in Spread Spectrum Time-Domain Reflection and Transmission Measurements

Spread Spectrum Time Domain Reflectometry (SSTDR) offers a new non-intrusive measurement technique for microwave imaging. While vector network analyzers (VNAs) are conventional tools in this domain, they present significant drawbacks such as high cost and lengthy scan times. This paper explores the viability of substituting SSTDR devices for the VNA by validating their accuracy in comparison to traditional VNAs in the 0.5-4 GHz band. We conducted several tests of reflection and transmission measurements of RC loads, analysis of variations due to cable movement, calibration consistency, and temperature-induced variations. We also measured antenna <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S₁₁</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S₂₁</i> in two oil-based phantoms to simulate human breast tissue, comparing changes with the insertion of a metal tumor substitute. We found the mean confidence intervals of the VNA and SSTDR are better (less) than 0.03 for the |<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S₁₁</i>| and 0.02 for the |<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S₂₁</i>| from 0.5-4 GHz, and that metal “tumors” in the oil are detectable. These results suggest that SSTDR may be a viable alternative to VNAs for applications such as microwave breast imaging, warranting further investigation in more robust setups.