Broadband capacitively grounded coplanar to coupled microstrip transition for planar microwave photonic components

Broadband transitions are presented in this paper for capacitively grounded coplanar waveguide to coupled microstrip (CMS) lines. These transitions are realized on both thick Rogers RO3003 substrate (thickness of 10 mils) and a thin benzocyclobutene (BCB) polymer film (thickness of 20 µm). A flat bandwidth of 4–20 GHz and 3.2 to over 40 GHz are measured for the RO3003 and BCB polymer substrates, respectively. These performances are obtained without making via-hole in the substrate or patterning the bottom ground plane, which makes this broadband transition easier to fabricate compared with the via-hole-based grounded CPW–CMS transitions.