Abstract: A microwave circuit has a flat dielectric substrate with one face carrying a grounded metallic layer partly broken away to leave room for a multiplicity of conductor strips coplanar therewith which form part of one or more transmission lines having input and output ends each comprising an ungrounded strip portion flanked by two zones of the grounded layer. Electrical continuity between separated portions of that layer, and/or between nonadjacent conductor strips, is established by short-circuiting wires jumping across intervening strip sections. With coupled transmission lines operating with different modes of propagation, this structure substantially equalizes their respective phase velocities.