Effects of the bottom ground plate on CPW bound modes

As it is well known, conventional coplanar waveguides support two bound modes at relatively low frequencies. However, conductor-backed coplanar waveguides printed on single-layer dielectric substrates can not support proper modes due to the existence of a TEM mode of the background parallel-plate waveguide. In this work we investigate the transition from a conventional coplanar waveguide to a conductor-backed coplanar waveguide by placing a ground plane at a decreasing distance from the dielectric substrate. We will study both the evolution of the modes of the coplanar waveguide and the voltage signal excited on the line by canonical delta-gap current sources.