论文部分内容阅读
在微波波段,用于标定温度和辐射功率的发射率接近于1的标准发射率器件,即微波频段的黑体,结构形式一般为表面涂覆吸波材料的金属锥体阵列.这种黑体器件常用于为微波辐射计提供参考亮温,要求具有高发射率和均匀的温度分布.对此类黑体器件的发射率评估主要基于基尔霍夫热平衡定律,即通过评估反射率来确定发射率.已报道的研究集中在黑体发射率随频率的变化趋势,较少针对其随方向和极化状态的变化趋势.本文针对此类周期型排布的黑体,提出基于Floquet模式分析的反射率评估方法,相比已报道的基于后向散射的评估方法,具有更大的适用范围.基于这种方法,对某黑体的发射率随频率、角度和极化状态的变化规律进行了计算分析.分析结果表明:此黑体发射率在X到K_a波段内随频率提高而增大;在发射率较低的低频处,垂直极化与水平极化的发射率随俯仰角的变化趋势不同,并且存在垂直极化发射率随俯仰角增大而明显降低的现象.这些规律均与其物理上低频段内涂层对电磁波的衰减特性相符合.
In the microwave band, a standard emissivity device with a near-1 emissivity for calibration of temperature and radiated power, the blackbody in the microwave band, is typically a metal cone array with a surface coated with a wave absorbing material. In order to provide the reference radiance for the microwave radiometer, a high emissivity and a uniform temperature distribution are required. The emissivity evaluation of such a black body device is mainly based on Kirchhoff’s thermal equilibrium law, ie the emissivity is determined by evaluating the reflectance. The reported studies focus on the change tendency of the blackbody emissivity with frequency and less on its trend with the direction and polarization state.This paper presents a method for the reflectivity estimation based on the Floquet mode analysis for such periodic blackbody arrangement, Compared with the reported method based on backscatter estimation, it has a bigger scope of application.According to this method, the emissivity of a blackbody is calculated and analyzed with the change of frequency, angle and polarization state.The analysis results show that : This blackbody emissivity increases with increasing frequency in the X to K_a band. At low frequencies with low emissivity, the vertical and horizontal polarization emissivity vary with pitch angle , And there is a phenomenon that the vertical polarization emissivity decreases obviously with the increase of the pitch angle.These laws are consistent with the attenuation characteristics of the electromagnetic wave in the physical low frequency inner coating.