  We present a semianalytical method to obtain perfect transmission across
abrupt H-plane bends in single-mode rectangular waveguides using a single
passive polarizable element (scatterer). The underlying analysis and synthesis
schemes are inspired by the rapidly-growing research on metagratings, typically
used to manipulate wave trajectories in free-space. These sparse configurations
of subwavelength polarizable particles (meta-atoms) are designed by careful
tailoring of inter-element near-field and far-field interactions, relying on
analytical models to resolve the required meta-atom distribution and geometry
to facilitate a desired interference pattern when excited by the incident wave.
Utilizing these metagrating design concepts, we develop a modal formalism for
obtaining a collection of locations inside the bend junction, in which a
passive scatterer may be placed to zero out the return loss. Subsequently, we
propose two different shapes for the scatterer and discuss, for each of them,
the ways in which their geometrical characteristics may be retrieved. This
versatile and efficient methodology, verified via full-wave simulations, can be
utilized to eliminate reflection loss in diverse bend configurations, often
found in complex wave-guiding systems used for antenna feeding and power
transmission. Moreover, these results demonstrate the usefulness and potential
of metagrating design concepts for various applications, beyond free-space beam
manipulation.
