A microwave transmission line structure having a pair of ground strip conductors on a surface of a dielectric substrate structure. A signal strip conductor is disposed on the surface of the dielectric substrate structure between the pair of ground strip conductors. A solid dielectric layer is disposed over: the signal strip conductor; the upper surface of the dielectric substrate structure between sides of each one of the ground strip conductors; and the signal strip conductor. An electrically conductive shield member is disposed on the solid dielectric layer and on, and in direct contact with, upper surfaces of the pair of ground strip conductors. The structure is used on each one of a plurality of proximate microwave transmission lines formed on the substrate structure to electrically isolate the transmission line.