Impedance calculations for modified coplanar waveguides

In view of the fact that recessed-gale FETs (Furutsuka et al, 1979 HILBERG , W. , 1969 , From approximations to exact relations for characteristic inpedances . I.E.E.E. Transactions on Microwave Theory and Techniques , 17 , 259 – 265 .[Crossref] , [Google Scholar]) can sustain higher breakdown voltages and hence more power than conventional FETs, it is important to design new microwave transmission lines compatible with recessed-gate 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 sufficiently small so that conformal mapping techniques suitable for a quasi-static mode can be applied.