Electromagnetic Design of Calibration Targets for MetOp-SG Microwave Instruments

We describe the electromagnetic development of microwave calibration units for the second generation of meteorological operational satellites. In particular, we focus on the electromagnetic and thermal design of on-board calibration targets (OBCT) for the microwave sounder (MWS) and the ice cloud imager (ICI), respectively. The OBCTs act as temperature reference for calibration. Therefore, they are required to exhibit a low electromagnetic reflectivity and a uniform temperature. This paper discusses the numerical design of pyramid absorbers for MWS and ICI. Based on theoretical studies, we have developed a novel pyramid design, which exhibits superior electromagnetic and thermal properties compared with conventionally used layouts. A comprehensive numerical study on the impact of common types of manufacturing tolerances has been carried out, and the most critical types were identified. This work presents remedies that reduce the susceptibility to manufacturing tolerances. All numerical results have been verified experimentally, and the manufactured OBCT prototypes have been shown to fulfill the specific requirements in all frequency bands.