Abstract
When using traditional methods to measure the microwave/millimeter-wave emissivity of small targets, errors arise due to that the antenna's main lobe and side lobe cannot be completely covered by the target. To eliminate the errors exist in traditional measurement methods, this paper first analyzes the main sources of errors and gives the analytical expression of the errors. On this basis, an improved method named voltage method is proposed. To test the effectiveness of the improved method, the horizontal polarization emissivity and the vertical polarization emissivity of a metal plate coat with stealthy nano-materials were measured at different observation angles by voltage method and traditional method, respectively. A dick radiometer working in 35 GHz is used in the experiments. Simultaneously, the accurate emissivities of the target are obtained by standard arch method. The results show that the voltage method improves the measurement accuracy largely compared to the traditional method.
Highlights
Passive microwave/millimeter-wave (PMW/PMMW) technology has been widely used in many applications since it can penetrate smoke, fog, clothing, and can work day and night [1]–[6]
Tph is usually obtained by measuring the physical temperature of the target surface, and the results can be equated with the brightness temperature (BT) of blackbody at the same temperature
MEASUREMENT UNCERTAINTY In voltage method, the blackbody is approximated to an ideal radiator, the metal plate is approximated to an ideal reflector, and the physical temperature of the blackbody is the same as that of the target to be measured
Summary
Passive microwave/millimeter-wave (PMW/PMMW) technology has been widely used in many applications since it can penetrate smoke, fog, clothing, and can work day and night [1]–[6]. Tph is usually obtained by measuring the physical temperature of the target surface, and the results can be equated with the BT of blackbody at the same temperature. The emission BT of the background reflected by the target needs direct measurement, and the result can be expressed as TAbg =. The voltage method does not need to measure the radiation of background and the physical temperature of the targets’ surface directly, and the errors arose due to that the antenna’s main lobe and side lobe cannot be completely covered by the target can be eliminated in this method by measuring the blackbody and metal plate of the same size as the target sample. The traditional method needs to convert the measured voltage values to the BT through the calibration, and calculate the emissivity, the voltage values can be used to calculate the emissivity directly in voltage method
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