Monostatic Free-Space Method for Relative Permittivity Determination Using Horn Antenna Near-Field Measurements

This paper presents a free-space method for the measurement of the relative permittivity of planar low-loss materials, using one-port scattering parameters. The proposed method estimates the dielectric constant value of a material under test (MUT) with a thickness of more than half of a wavelength, placed in front of an X-band pyramidal-horn antenna. The calculation leverages the frequency points where the reflection coefficient's magnitude (|S ₁₁ |) is the lowest while disregarding any system pre-calibration measurements. The free-space setup was tested on multiple materials with a wide range of electric permittivity values, where accurate estimation results of dielectric constants were obtained.