A signal distribution structure including: a dielectric material; an overlying conducting layer on a first level of the dielectric material; a first signal line on a second level of the dielectric material, the first signal line being physically separated from the overlying conducting layer by the dielectric material; wherein the overlying conducting layer includes a window running parallel to the first signal line, and further comprising within the window a first coupler electrode on the first level of the dielectric material, the first coupler electrode above, parallel to, and electrically isolated by the dielectric material from the first signal line, wherein the first coupler electrode is electrically isolated from the overlying conducting layer along at least most of its periphery.