A Free Space Method for Measuring Material Constants Using a Moving Reflector in Millimeter-Wave Bands

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  • 自由空間法における移動反射板を用いたミリ波帯材料定数の測定法

Abstract

In millimeter-wave radar installed in automobiles, it is important to measure the material constants (relative permittivity and dielectric tangent tan δ) of the radar dome that covers the radar, because they directly affect the radar performance. This paper proposes a free-space method for measuring the material constants using a moving reflector in the millimeter-wave bands, in which the transmission coefficient of a sample is calculated from the reflection signal of the linearly moving reflector by detecting the phase change and amplitude of the received signal due to the reflection of the reflector as it moves. The method does not use a vector network analyzer (VNA) and does not require calibration before the measurement, so the material constants can be determined quickly. 5 types of samples, including acrylic substrate and indium phosphide (InP) wafer, were measured as examples in the 76 GHz band. The results show that the measurement method proposed in this paper is as accurate as the S-parameter measurement method using VNA.

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