Guided-Wave Absorption in Rectangular Waveguide Using Lossy Metagratings

We present a design for a perfectly absorptive waveguide by utilizing lossy metagratings. The waveguide, standard WR90 operating in the X-band, achieves perfect absorption at 10 GHz through destructive interference between the reflection at the waveguide end and the metagrating's excitation field. The TE <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }_{10}$</tex> mode is effectively absorbed, enabling the waveguide to function as a perfect absorber. Two types of meta-atoms are tested for the ultra-thin metagrating: a series combination of a strip capacitor and chip resistor, and an Indium Tin Oxide (ITO) film-based line. The proposed design is scalable across a broad frequency range, from microwaves to millimeter waves thanks to it simplicity and ease of fabrication. Such absorptive waveguides show significant potential for applications in reflectionless filters, leaky-wave antennas, and other guided-wave devices.