Experimental study of the effect of ground width for millimetre-wave multilayer coplanar waveguides in ceramic multichip module technology

This study presents the accurate characterisation and detailed experimental study of the effect of ground-plane width and suppression of higher-order parasitic modes extending the frequency of operation up to 110 GHz for multilayer conductorbacked coplanar waveguide lines, fabricated in cost-effective thick-film multichip module (MCM) technology. The coplanar waveguides (CPWs) and components have been realised on multiple layers of dielectric onto a ceramic substrate using straightforward and cost-effective photoimageable thick-film process, demonstrating a very low loss of ,0.2 dB/mm at 80 GHz for a finite ground CPW and extremely low loss of ,0.1 dB at 76 GHz for CPW layer transitions, which are better than many reported results for MCM technologies. Further, the effective dielectric constant (ε_eff) and characteristic impedance (Z_ch) are extracted from two-port S-parameters measured on a single-line and by conversion to ABCD parameters, to investigate the practical effect of ground-plane width on CPWs on a multilayer ceramic substrate and to facilitate realisation of a cost-effective millimetre-wave MCM.