  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.
