Effects of Coating Material Properties on the Wideband Reflectivity Performance of Microwave Calibration Targets

This communication investigates the wideband reflectivity performance of calibration targets for spaceborne radiometers, which are fabricated as coated pyramids/cones. Specifically, the effects of the coating material properties on the wideband reflectivity performance are studied. Numerical studies based on finite-difference time-domain (FDTD) methods are carried out considering two coating materials with distinct characteristics. The mechanisms of structural absorption and reflection in both the low- and the high-frequency regions are discussed, and the relations between the coating material properties and the total reflectivity are determined. The results show that the absorption within the coating layer is not the only factor that determines the structural reflection in the high-frequency region; the impedance matching between the coating and free space, especially in the case of coated pyramids, is also a determinant. Different geometry optimization strategies are presented for the two materials based on their distinct characteristics. The wideband reflectivity performance is found to be well improved.