An integrated circuit includes a silicon-on-insulator wafer and interconnect layer providing a support for a coplanar waveguide formed above a top side of the support. A through-silicon via is formed from a back side of the support and passing through the silicon-on-insulator wafer to reach the interconnect layer. A trench is formed from the back side of the support underneath the coplanar waveguide. The trench extends over at least an entire length of the coplanar waveguide. The trench passes through the silicon-on-insulator wafer to reach the interconnect layer and may have a substantially same depth as the through-silicon via.