Physical model for evaluating propagation loss of metal-coated dielectric terahertz waveguides

Propagation loss of Au-coated parallel-plate waveguides was studied. A physical model to evaluate propagation loss was derived and experimentally validated. It revealed that the electrical conductivity of the coating metal, which differs from the bulk conductivity and depends on film thickness due to the thin- film effect, is the dominant factor determining the loss in addition to film thickness. Our model enables us to anticipate the propagation loss in the metal-coated dielectric waveguides with various film thickness, frequency, coating metal, and waveguide geometry using experimentally obtained film thickness and its thickness-dependent conductivity.