volume | PIER Journals

Abstract

This paper proposes an investigation in the terahertz (THz) frequency range of the dispersion and an individual quantitative treatment of the losses of the most classical microwave waveguides (coplanar, slotline, microstrip and stripline) numerically led in three dimensions (3D). An original strategy has been used to quantify radiation losses associated with leaky modes. A very low THz permittivity polymer (benzocyclobutene (BCB)) was used as a very convenient substrate to be easily grafted as a THz environment of integrated passive or/and active devices. Direct comparisons of the losses and the dispersion have been performed following two criteria: a constant characteristic impedance Z_c fixed at 100 Ω and a constant effective width Weff fixed at 30 μm. The best waveguides are microstrip (α_T= 2.52 dB/mm for Z_c= 100 Ω and for W/H=35/50 μm (with W the strip width and H the substrate height) and α_T =2.29 dB/mm for W_eff = 30 μm at 1 THz with H = 30 μm) and stripline (with quasi-null radiation losses and the best quality factor Q_T= 63 for Z_c = 100 Ω). The large dispersion and radiation losses of the slotline (SL) can be reduced with a thick BCB encapsulation to enhance the THz signal. The coplanar waveguide (CPW) remains in a medium position. Besides the parasitic mode (SL) and low Q_T problems due to mainly ohmic losses, its major advantage is its planar geometry allowing to an easy circuit integration with THz sources, amplifiers and detectors based on semiconductor. Consequently, these THz studies on BCB microwave standard waveguides open to various perspectives to carry out a broad panel of integrated THz circuits.

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Dr. Lei Cao

Dr. Anne-Sophie Grimault-Jacquin

Dr. Frederic Aniel