Coplanar waveguide to microstrip transition in thin polymer film for characterization and packaging of microwave photonic components

We report in this paper two types of broadband transitions between microstrip and coplanar lines on thin benzocyclobutene (BCB) polymer substrate. They are both via-free, using electromagnetic coupling between the bottom and top ground planes, which simplifies the manufacturing of components driven by microstrip electrodes. In the first ones, the bottom ground is not patterned, which makes them particularly suitable to on-wafer measurement of components under development with coplanar probes. An ultra-broad bandwidth of 68 GHz (from 1 GHz to 69 GHz) was achieved with 20-pm BCB. In the second ones, intended for connectorizing components on thin substrate with coplanar connectors, the bottom ground is patterned to match the narrow center conductor (54 μm) on thin substrate to the wide center conductor (127 μm) of the connector with a tapered section, achieving to a experimental bandwidth 13 GHz for the moment.