Printable Planar Dielectric Waveguides Based on High-Permittivity Films

Planar microwave components are very desirable for many applications and are mainly realized by metallic structures. In this work, a planar dielectric waveguide is proposed. A high-permittivity micrometer-size thick film is patterned on a low-loss microwave substrate and is considered as a nearly perfect magnetic wall to realize the waveguide structure. The permittivity contrast between the film and substrate is kept high (e.g., > 30) in order to minimize the leakage power, and consequently, the insertion loss. The waveguide structure is theoretically analyzed using an approximation method and the results are confirmed by a simulation-based numerical method. The impact of dielectric loss of the film in waveguide performance is much less than that of the substrate, allowing waveguides with films having a medium or high loss (e.g., ε^´´ = 3) result in a low insertion loss (e.g., up to 0.04 dB/mm at 40 GHz). Several prototypes are fabricated by screen-printing of barium-strontium-titanate (BST) pastes and characterized at 40 GHz. Using the extremely lossy BST film (tanδ = 0.2, ε^´´ = 70), the insertion loss of the waveguide is measured to be 0.18 dB/mm. Based on the current technologies, the printable planar dielectric waveguide can achieve 0.08 dB/mm in insertion loss. Further improvements are expected in the future as the materials and fabrication technologies progress.