COMPARISON AND OPTIMIZATION OF DISPERSION, AND LOSSES OF PLANAR WAVEGUIDES ON BENZOCYCLOBUTENE (BCB) AT THZ FREQUENCIES: COPLANAR WAVEGUIDE (CPW), MICROSTRIP, STRIPLINE AND SLOTLINE

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 Zc flxed at 100› and a constant efiective width Wefi flxed at 30m. The best waveguides are microstrip (fiT = 2:52dB/mm for Zc = 100› and for W=H = 35=50m (with W the strip width and H the substrate height) and fiT = 2:29dB/mm for Wefi = 30m at 1THz with H = 30m) and stripline (with quasi-null radiation losses and the best quality factor QT = 63 for Zc = 100›). 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 QT problems due to mainly ohmic losses, its major advantage is its planar geometry allowing to an easy circuit integration with THz sources, ampliflers 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.