自由空间单站反射系数测量中校准方法的比较

Comparison of Calibration Methods in Free-Space Monostatic Reflection Coefficient Measurement

微波黑体为微波辐射计提供高精度的亮温信号以精确标定观测目标的辐射信号幅度。微波黑体的发射率是影响其辐射特性的重要参数,因此准确测量黑体发射率对于提高辐射计的定标精度和保证量值的溯源性和有效传递具有重要意义,目前黑体发射率主要通过测量反射率来间接计算得到。本文实现了自由空间单站反射系数测量中的两种校准方法:偏移短路校准法和滑动负载校准法,采用时域门技术解决了小反射测量过程中多径反射信号的影响。搭建了反射率测量系统,在75~110 GHz频段内测量了同一黑体目标的反射率,并对测量结果进行了分析和比较。两种校准方法解算的误差项具有很好的一致性,测量发射率均能到达0.999~0.9999量级。当被测黑体满足近似条件时,使用滑动负载校准法具有更高的效率。最后,以偏移短路法为例,采用蒙特卡洛方法对微波黑体反射系数的测量不确定度进行了评定。

Microwave blackbodies provide high-precision brightness temperature signals for microwave radiometers to accurately calibrate observed target radiation signals.The emissivity of a microwave blackbody is a crucial parameter affecting its radiative characteristics.Therefore,accurately measuring blackbody emissivity is significant for enhancing radiometer calibration precision and ensuring measurement value traceability and effective transfer.Currently,blackbody emissivity is mainly obtained indirectly by measuring reflectivity.This study implements two calibration methods in freespace monostatic reflection coefficient measurement:the offset-short calibration method and the sliding-load calibration method.Time-domain gating techniques are utilized to address multipath reflection signals during small reflection measurements.A reflectivity measurement system was established,and the reflectivity of the same blackbody target was measured within the 75-110 GHz frequency band,with results analyzed and compared.The error terms solved by the two calibration methods exhibit high consistency,with measured emissivity reaching levels of 0.999-0.9999.When the measurement target satisfies approximation conditions,the sliding-load calibration method proves more efficient.Finally,using the offset-short method as an example,the Monte Carlo method was employed to evaluate the uncertainty of the solved blackbody target reflection coefficient.