On the Reflectivity Extraction Based on Partial Bistatic Near-Field Scattering from Microwave Blackbody

This work reports numerical investigations on the scattering from microwave blackbody, for developing a national standard facility on the emissivity determination in China. Based on the Kirchhoff's law of thermal equilibrium, the standard facility follows a bistatic scattering measurement configuration and covers a wide frequency range. In general, the reflectivity is to be extracted based on partially collected scattering in the near-field region. The whole electromagnetic process, from the quasi-optical antenna illumination, to target scattering, and finally the aperture coupling reception, is modeled to be analyzed. It is shown in the simulation results that the Floquet scattering properties of the array-shaped blackbody can be obtained without fulfilling the far-field condition. Then, evaluations on the reflectivity extraction are performed at 54, 89, 118, and 183 GHz, addressing typical blackbody structures of coated cones and coated pyramids. The factors of referencing targets, curve integration, and the oblique incidence are discussed, as well as the case of geometry flawed blackbody. This work offers important reference and specific suggestions for achieving accurate and stable reflectivity determination in the bistatic near-field configuration.