A new mode-coupling effect on coplanar waveguides of finite width

A novel mode-coupling effect that occurs on conventional coplanar waveguides of finite width is identified and explained. The coupling occurs between the standard CPW dominant mode and a newly identified dominant mode called the CPW dominant surface-wave-like mode. This coupling is different from that which is known to occur when a printed-circuit waveguide is placed in a box or package; here, there is no box, and the finite width by itself is sufficient to produce the coupling effect. Other physical effects are included in order to place the coupling effect in perspective.<>