A Free-Space Measurement Method for the Low-Loss Dielectric Characterization Without Prior Need for Sample Thickness Data

摘要

A free-space measurement method is presented for the characterization of low-loss dielectric materials at millimeter-wave frequencies that does not require any assumption of a priori knowledge of the sample thickness. The method first employs only maximal and minimal envelopes of measured transmission scattering parameters to determine the real part εr' of the permittivity of test materials. Subsequently, the thickness of the sample is estimated from εr' and frequencies for maximal and minimal peaks of the transmission scattering parameter. The calculation of the imaginary part εr" of the permittivity then easily follows. Our method is examined by measuring two cross-linked polystyrene samples, one polytetrafluoroethylene sample and one polymethylpentene sample in the frequency range of 220-325 GHz at the incident angles of 0°, 10°, 20°, and 30°. Moreover, an explicit uncertainty analysis for the permittivity is derived, and uncertainties of the extracted complex permittivity are reported.