Low-loss flexible dielectric waveguide for millimeter-wave transmission and its application to devices

Flexible dielectric waveguides have been fabricated for use at 94 GHz and 10 GHz by filling Teflon tubing with high dielectric constant powders. Losses as low as 0.18 dB/cm were measured at 94 GHz with these flexible guides. The theoretical expressions for a round dielectric waveguide with a finite thickness cladding were reviewed, and numerical calculations based on this theory gave good agreement with guide wavelength values measured on the 10 GHz guides. Shorted waveguide measurements at 10 GHz were used to determine dielectric constant as a function of powder density for various low-loss powders: Trans-Tech D-8512 barium tetratitanate, Trans-Tech D-38 barium tetratitanate, Trans-Tech D-30 nickel aluminum titatanate, Trans-Tech MCT-40 magnesium calcium titanate, and Emerson and Cuming Ecco-Flo. Guide wavelengths were also measured for waveguides made by filling rectangular grooves (approximately 1mm x 1mm) in Teflon substrates with low-loss powders. These measured wavelengths were compared to those predicted by the approximate theory of Marcatili.