Thin film tunnels versus air-bridges in coplanar waveguide discontinuities

In this paper, a new method for the suppression of the slot line (odd) mode in the CPW based microwave circuits is presented. The proposed method replaces the costly and mechanically unstable air-bridges. It uses an under pass (tunnel) on an intermediate metalization layer below the CPW line and above the substrate. This method is convenient for MCM-D technology in which thin films are deposited over the substrate to support the required interconnects. The method has been applied to a band reject filter and compared with the case of air bridges.