Gore study contrasts VNAs and TDRs

The goal of the study was to determine whether the instruments possess similar levels of measurement precision.

By Rick Nelson, Chief Editor -- Test & Measurement World, 7/1/2010 12:00:00 AM

W.L. Gore has released the results of a study in which its engineers compared the measurement uncertainty of VNAs (vector network analyzers) and TDRs (time-domain reflectometers)—two instruments able to analyze time or frequency domain data to accelerate product-development cycles. The goal of the study was to determine whether the instruments possess similar levels of measurement precision.

TDRs and VNAs are formidable instruments. Engineers at W.L. Gore & Associates conducted a study to determine how they compare with respect to measurement uncertainty.

Using a variety of cable assemblies with a range of insertion loss and VSWR (voltage standing-wave ratio) characteristics, the engineers initially tested six cable assemblies in controlled conditions on each instrument. Next, they evaluated the instruments' measurement uncertainty in the best-case scenario with the highest-performing assembly. Then, to ensure TDR/VNA test parity, they evaluated the VNA using both one-port s₁₁ reflection and the more traditional two-port s₂₁ transmission method.

Among the study's findings: "In both the TDR and VNA, instrument-related measurement uncertainty was found to be dependent upon the device under test's VSWR and insertion loss. The median measurement uncertainty for the VNA was found to be an order of magnitude below that of the TDR...." In addition, "TDR instrument-related uncertainty accounted for 61 percent of the total measurement uncertainty. VNA instrument-related uncertainty made up 22 percent of the total uncertainty."

Said Paul Pino, the company's North American product engineer for test and measurement, "Because precision is crucial in this industry, understanding the accuracy of an instrument is essential. Although our study indicated that one platform operated with significantly lower measurement uncertainty than the other, the important learning from this study is that both instruments are formidable tools, with each having its own strengths and weaknesses."

You can download the complete 18-page study at gore.com/measurement.