Free-Space Two-Tier One-Port Calibration Using a Planar Offset Short for Material Measurement

The scattering parameters of a material under test (MUT) are prerequisites for characterizing the material parameters of the MUT. This paper describes a free-space two-tier one-port calibration method using a planar offset short as a free-space calculable reflect standard for measuring the scattering parameters of an MUT from the two successive one-port calibrations of a free-space material measurement system without a precise positioning system in free space. The two-tier one-port calibration method is validated by comparing the measurement results with those of the thru-reflect-line (TRL) calibration method for two reciprocal MUTs (glass plates of 2.780 mm and 4.775 mm thickness) in the W-band (75–110 GHz). Good agreement between the measurement results from the two calibration methods demonstrates that the free-space two-tier one-port calibration method using a planar offset short can be a feasible and effective alternative to the conventional free-space two-port calibration methods.