Guided Mode Analysis of NRD Guide Using Efficient FEM with Impedance Boundary Conditions for THz Applications

Numerical modeling of very thin structures, specifically in the THz region, required extremely fine discretization, which increased both the complexity and the computing cost. Impedance boundary conditions are a promising method for the accurate modeling of waveguides without any discretization due to their high level of accuracy, ease of implementation, and low computation cost. In this paper, we developed a finite element method with impedance boundary conditions for modeling NRD guides, taking into account conduction loss, which is not ignorable in the THz domain. In order to show the effectiveness of the proposed technique, we performed a guided mode analysis of the NRD guide for both hybrid LSM $_{01}$ and parasitic LSE $_{01}$ modes. Excellent accuracy and very low computational cost are confirmed by comparing the results obtained by the proposed technique with conventional 3D-FEM. In addition, we also proposed the modified structure of the NRD guide, which greatly reduces the loss compared to the conventional one. The proposed technique and structure may have a potential for various high-performance NRD guide devices for 6G integrated circuit applications and beyond.