Eliminating Reflections in Waveguide Bends Using a Metagrating-Inspired Semianalytical Methodology

Abstract: 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.