Propagation characteristics of shielded coplanar transmission lines

Coplanar waveguides (CPW´s) have received considerable attention due to several advantages offered over conventional microstrips especially for MMIC´s applicat s on GaAs substrates. There principal advantage is the location of the signal grounds on the same substrate surface as the signal line, eliminating in that way the need for via holes and reducing the parasitic inductance which occurs in grounding FETs. One disadvantage of the of the CPW´s is that both an even and an odd made can exist due to the dual slot-line geometry of the structure. The latter mode is removed by short circuiting it with air bridges.