Specular Reflectance Measurements of Dielectric Plates in Millimeter Frequency Range

Abstract

I. INTRODUCTIONRecently, uses and applications of electromagnetic (EM) materials, devices, and systems have been becoming more popular in the fields of both the natural sciences, such as physics, chemistry, biology, earth science, and astronomy, and the application sciences, such as telecommunications, military, defense, security, transportation, and medicine. Their bandwidths have been broadening and operating frequency bands have been moving to the submillimeter frequency range. Measurements of the electrical properties of EM materials have gained considerable importance, particularly in the millimeter and submillimeter frequency ranges, as material parameters are fundamental parameters in the natural and application sciences fields [1,2].Various methods have been developed in millimeter and submillimeter frequency ranges to measure material properties (usually complex permittivity and permeability), e.g., the open resonator [3,4], free space [5][6][7][8][9][10], and reflection ellipsometry methods [11][12][13]. The open resonator method provides accurate material properties at discrete resonance frequencies. The free space method is based on the quasi-optic approach where the material under test (MUT) is coupled to transmit (Tx) and 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. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ⓒ

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