Unveiling the properties of metagratings via a detailed analytical model for synthesis and analysis

Abstract: We present detailed analytical modelling and in-depth investigation of wide-angle reflect-mode metagrating beam splitters. These recently introduced ultrathin devices are capable of implementing intricate diffraction engineering functionalities with only a single meta-atom per macro-period, making them considerably simpler to synthesize than conventional metasurfaces. We extend upon recent work and focus on electrically-polarizable metagratings, comprised of loaded conducting wires in front of a perfect elecric conductor, excited by transverse-electric polarized fields, which are more practical for planar fabrication. The derivation further relates the metagrating performance parameters to the individual meta-atom load, facilitating an efficient semianalytical synthesis scheme to determine the required conductor geometry for achieving optimal beam splitting. Subsequently, we utilize the model to analyze the effects of realistic conductor losses, reactance deviations, and frequency shifts on the device performance, and reveal that metagratings feature preferable working points, in which the sensitivity to these non-idealities is rather low. The analytical relations shed light on the physical origin of this phenomenon, associating it with fundamental interference processes taking place in the device. These results, verified via full-wave simulations of realistic physical structures, yield a set of efficient engineering tools, as well as profound physical intuition, for devising future metagrating devices, with immense potential for microwave, terahertz, and optical beam-manipulation applications.