Electrical properties of materials are requisite to analysis and design electromagnetic (EM) devices and systems. Free-space material measurement method, where the measurand is the free-space scattering parameters of an MUT (Material Under Test) located at the middle of transmit (Tx)/receive (Rx) antennas, is suitable for non-destructively testing the MUT without prior machining and physical contact in high frequencies. This paper proposes a free-space SOLR (Short-Open-Load-Reciprocal or unknown thru) calibration method using three planar offset shorts with the respective offset of (0, λ/6, 2λ/6) for calibrating a free-space material measurement system and measurement results of a glass plate of 4.775 mm thickness are shown in W-band (75–110 GHz).
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