Direct Modeling of Thermal-Radiation Reception by Antenna in Close Range

In this work, an interesting near-field propagation problem in the microwave radiometer calibration is addressed, which is the antenna reception of thermal radiation from calibration target. Efforts in simultaneously modeling the target and antenna within the same 2-D full-wave scenario are reported. Specifically, the coated pyramids and horn antennas are considered. Based on the incoherent nature of local thermal sources in the coating layer and the fluctuation-dissipation theorem (FDT), the direct modeling of receiving power and further brightness temperature (
$BT$
) at the antenna waveguide port can be achieved. The direct modeling is then quantified based on the classic concept of antenna reception in an ideal blackbody chamber. Further, it is shown in the results that mutual coupling affects the antenna reception in a fluctuating manner, and the target structural radiation raises the antenna reception in a very close distance. That means, the thermal reception can be affected by both the antenna and target structures in the near field. Also, the Lambertian radiation properties of the coated pyramidal blackbody are clarified in the direct calculated results. This work reveals the complex scenario of close range
$BT$
transfer, and opens the possibility of quantitatively modeling it for practical applications with further investigations.