Measurements of <i>S</i> -Parameters in the Free-Space Using a Virtual Reflect

This work introduces a method to measure S-parameters in free space using a Virtual Reflect (VR) generated from a symmetric single-ended Thru measurement. Time-domain analysis shows that the VR accurately replicates the behavior of a physical Reflect. The calibration process was experimentally validated using two approaches, the first involved analyzing the Thru configuration, and the second consisted of measuring the scattering parameters of six Material Under Test (MUTs), showing strong correlation with those derived from the conventional TRL method. Specifically, coefficients of determination (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>) exceeding 0.9203 were achieved for both magnitude and phase, while the Root Mean Square Error (RMSE) reached maximum values of 2.2686 dB and 5.4644° for magnitude and phase, respectively. The proposed method eliminates the need for a metal plate as a physical Reflect standard, reducing errors and simplifying measurements. It also requires fewer standards, shortens measurement time, and is less sensitive to antenna misalignments. An open-source software tool is provided as well.