Specular Reflectance Measurements of Dielectric Plates in Millimeter Frequency Range

This paper describes specular reflectance measurements of dielectric plates in three waveguide frequency bands: D-band (110–170 GHz), G-band (140–220 GHz), and J-band (220–325 GHz). The transmit (Tx) part of the proposed specular reflectance measurement system is stationary, while the receive (Rx) part and the material under test (MUT) holder are concentric-rotating with a 2:1 speed ratio for specular reflectance measurements. In specular reflectance measurements, the first step measures the specular reflection coefficients of an MUT and a metal plate on the MUT holder located at the center of the Tx and Rx parts, and the second step calculates the specular reflectance defined by the specular reflection power (i.e., intensity) of the MUT normalized to that of the metal plate. Multiple reflection effects between the Tx and Rx antennas and the MUT on the measured specular reflectance are minimized by averaging out the multiple specular reflectances measured with changing the separation distance between the two antennas by λ/8 intervals. Measurement results of the perpendicular-polarized specular reflectance of commonly used dielectric plates are verified by comparing those with the analytic results and show that the results measured over the overlapped frequency range of the D-/G-bands and at the boundary frequency of the G-/J-bands agree well with the results for the other band, respectively.