Impedance calculations for modified coplanar waveguides

Abstract

In view of the fact that recessed-gate FETs (Furutsuka et al. 1979) can sustain higher breakdown voltages and hence more power than conventional FETs, it is important to design new microwave transmission lines compatible with recessedgate FETs on GaAs monolithic integrated circuits (MICs). Structures and impedances of three modified coplanar waveguides (CPWs) are presented here: (1) a finite-thickness CPW with a third ground plane for improved heat-sinking, (2) an abrupt-recessed strip CPW, and (3) a graded-recessed strip CPW. All of the above CPWs are structured to fit the recessed-gate FETs on MICs. The gap dimensions of the structures are assumed to be sufliciently small so that conformal mapping techniques suitable for a quasi-static mode can be applied.

Determining complex permittivity from propagation constant measurements with planar transmission lines

“…Furthermore, this assumption requires that the gap region that is formed between the conductors (due to their finite thickness) is either filled with the material to be measured (a simple task in the case of liquid and semisolid sample materials) or with an additional material after manufacture (e.g., epoxy resin). Alternatively, the planar lines could be manufactured so that they are embedded in the substrate material, flush with the top face of the substrate [10]. For these situations ε * eff is a linear function of ε * , namely,…”

CAD modeling of coplanar waveguide cross-over air-bridge

“…To our knowledge, no closed-form expressions for the effective dielectric constant and the characteristic impedance of the ES-CPW are available. Based on conformal-mapping analysis of the recessed strip CPW in [13], we tried to use conformal mapping to obtain such expressions, but found out that this could be tedious and not really necessary for our air-bridge study, as will be shown below.…”