Study on the Measurement Method of Liquid Complex Refractive Index in Millimeter-Wave Band Based on Polarization Radiometry

A radiometer acquires information by capturing spontaneous radiation from the observation scene. In the microwave (MW)/millimeter-wave bands, brightness temperature (BT) is commonly used to characterize the radiation intensity of a scene. The BT of an object is related to its emissivity, which is governed by the electromagnetic parameters of the material. However, directly deriving accurate electromagnetic parameters of a material from measured BTs remains a significant challenge. This article proposes a novel methodology for retrieving material electromagnetic parameters by measuring polarization characteristic quantities at multiple observation angles via a radiometer. The underlying principle and detailed implementation workflow of this method are elaborated in this article, and its effectiveness and accuracy are verified through experiments. Furthermore, several main error sources in the method are analyzed. This method is expected to provide a reliable and cost-effective solution for the measurement of electromagnetic parameters in high-frequency bands.