Comparison of Two SOLR Calibration Approaches for Oscilloscope-Based S-Parameter Measurements

This work studies two calibration methods for S-parameter measurements by a real-time oscilloscope (RTO). Vector Network Analyser (VNA) measurements of an active and passive device, calibrated with an eight-term Short Open Load Reciprocal (SOLR) algorithm, are compared to RTO measurements with SOLR calibration applied via two methods from literature. The methods differ in the order of S-parameter calculation from the RTO measured travelling voltage waves and in their error models. Method one, the traditional method (TM), converts the raw waves to S-parameters before calibration and utilises the twelve-term model. Method two, relative wave calibration (RWC), corrects the raw waves via the eight-term model and calculates S-parameters at the end. The TM provided the closest match to VNA data with a maximum 2.31% error in transmission and so is recommended for RTO vector calibration.