Design, Fabrication and Integration of Rectangular TE₁₀ to Circular TE₁₁ Mode Waveguide Transition Adapter for Robust W-band Wired Terahertz Transmission System

Terahertz (THz) waveguide transition adapters (WTA) can realize the efficient connection of THz sources and THz transmission lines. This is pivotal to build robust THz wired transmission systems. In this study, rectangular-to-circular polymer/Ag WTAs were designed based on the finite element method (FEM) simulations for efficient transformation from rectangular TE₁₀ modes to circular TE₁₁ modes. The WTAs samples were fabricated via 3D printing and dynamic liquid-phase deposition methods. It was integrated with a 100 GHz THz source (WR-10 standard rectangular port) and a 4-mm-bore polypropylene (PP)/Ag flexible circular hollow waveguide (HWG). The transmission performance of the integrated THz delivery system was examined systematically. The output energy distribution of the WTA conformed to the circular TE₁₁ single-mode transmission. It could reduce the transmission loss of the straight-line system from 1.70 dB/m to 1.11 dB/m and enhance by 18.03% of the power coupling efficiency. The system was also robust for bending transmission and the additive bending loss was reduced from 1.45 dB/m to 0.92 dB/m under a 15 cm radius bending condition. The WTA developed in this study provides a feasible solution for efficient integration between HWGs and THz devices, which is currently in great need for constructing diverse sensing, 6G communication, and imaging systems based on THz transmission lines.