Dielectric Lined Waveguides for Low Loss Millimeter Wave and Terahertz Transmission

By coating the inside of an overmoded, smooth wall metallic waveguide with a thin dielectric layer, one can obtain similar boundary conditions to corrugated waveguides and achieve extremely low transmission loss propagating the HE11 mode. As presented here, dielectric lined waveguides are a cost-effective alternative to corrugated waveguides for broadband microwave transmission, particularly at frequencies above 300 GHz. A theoretical model provides an analytic method for computing attenuation. The propagation mode of a prototype dielectric lined waveguide is characterized using low power transmission measurements to analyze the beam radiated from the waveguide aperture. Results indicate HE11 mode purity of approximately 98%. Furthermore, we quantified attenuation with low power Fabry-Perot measurements, verifying low loss performance of the experimental prototype. These results demonstrate that dielectric lined waveguides could have applications in many fields demanding low attenuation millimeter and terahertz transmission, such as radar, high-frequency communication systems, THz dynamic nuclear polarization, and electron cyclotron heating in magnetically confined fusion experiments.