Capacitive transmission lines in coplanar waveguides for millimeter-wave integrated circuit design

For use in millimeter-wave integrated circuits, theoretical and experimental design data for various useful capacitive transmission lines in coplanar waveguide on gallium arsenide are presented. Multifinger and metal-insulator-metal (MIM) lines enabling low characteristic impedance in the order of 10 ohm as well as broad-band capacitive coupled transmission lines are investigated. Simple design rules and accurate models validated with measurements up to 120 GHz demonstrate that such planar transmission lines can be used in monolithic microwave integrated circuits (MMICs) to extend the impedance range and the design flexibility with respect to the conventional CPW.