Standard Protocol for De-Embedding S-Parameter Calibration Data on Test Benches
Stripping test fixture phase delay and magnitude loss from raw vector network analyzer measurements ensures true S-parameter extraction.
2xthru
Meaning
Printed circuit board test structures include a continuous transmission line designed with identical left and right connector ports. Testing laboratories use a 2xthru standard to calculate and remove the effects of test fixtures during vector network analyzer measurements.
Fixture Symmetry
Fabrication tolerances demand that the left and right halves of the trace are electrically identical. Engineers measure this structure to split the S-parameter response mathematically into two symmetrical halves. The physical length of the trace must equal exactly twice the length of one individual test fixture, ensuring that the reference plane sits precisely at the center of the line.
Coaxial to planar transitions must align perfectly to avoid phase mismatches that corrupt the mathematical separation of the test port.
Error Vector
Manufacturing variations can break the symmetry between the two halves of the test line. Solder mask thickness and fiber bundle effects introduce small discrepancies that degrade the mathematical accuracy of the split. Symmetrical routing reduces this issue.
Calibration Limit
High frequency measurements over forty gigahertz demand extremely short transition traces to minimize non-coaxial phase errors. The 2xthru calibration requires a single physical layout on the same board material to ensure representative results. Probe placement must remain highly repeatable.