Discussion on the Non-Lambertian Radiation Properties and Reception Configuration of the Metasurface Blackbody for Radiometer Calibration

Metasurfaces with high absorption characteristics can serve as blackbody calibration targets for microwave radiometers. Resonant metasurfaces with thin structures are especially attractive candidates due to their high cost-effectiveness and excellent temperature uniformity. However, such metasurfaces usually exhibit spatial dispersion in reflection, since their resonance conditions are strongly wave-vector dependent. This phenomenon affects the radiation behavior of metasurfaces when used as calibration targets and presents challenges to the calibration process, which are difficult to detect through monostatic measurements. This work first characterizes the highly directional, non-Lambertian radiation behavior of metasurface microwave calibration targets (MMCTs), then clarifies its impact on near-field brightness temperature (BT) transfer. Finally, the appropriate antenna configuration for effective deployment of MMCTs is identified. A specific metal-insulator-metal (MIM) prototype is taken as a representative example to illustrate this common issue. Near-field simulations and experiments are conducted. Results are obtained for the actual BT transfer from MMCT to near-field antennas of different apertures, as well as the engineering estimated BT with monostatic measurements. It is revealed that, collimated antennas are required for efficient BT transfer and accurate performance estimation of the MMCT.