Coplanar-waveguide tandem couplers with backside conductor

Novel tight coplanar-waveguide (CPW) directional couplers are developed by connecting two loose couplers in tandem configuration. In this study, the CPW tandem couplers without and with backside conductor are implemented on the FR4 substrate. These tandem couplers are carefully examined theoretically and experimentally, and good match between simulated and measured results is observed. The proposed tandem couplers have the merits of tight coupling under relaxed fabrication requirements.