Metasurface-based terahertz TE10-TE01 mode converter.

We designed a compact broadband mode converter based on metasurface technology, operating in the 180-210 GHz band (the effective bandwidth is approximately 22 GHz), which achieves high-efficiency conversion from the TE₁₀ mode in a standard WR-4 rectangular waveguide to the TE₀₁ mode in a circular waveguide. The mode converter consists of two sub-mode converters: the first, based on a magic-T waveguide, transforms the TE₁₀ mode into the TE₂₀ mode, and the second, based on a metasurface, converts the TE₂₀ mode into the TE₀₁ mode. Simulation results demonstrate that the conversion efficiency from the TE₁₀ mode to the TE₀₁ mode reaches a maximum of 88.3% (184.6 GHz), with a return loss 8.4%. This metasurface-based mode converter can replace traditional complex transitional waveguide structures, providing a solution for generating high-quality TE₀₁ mode in the terahertz band. Furthermore, the theoretical approach can be extended to the generation of other modes in the terahertz band.