Dispersion characteristics of multilayer microstrip lines with thin metal ground

The dispersion characteristics of multilayer open microstrip lines with a substrate of thin metal ground in the middle are studied using the spectral domain approach (SDA). The thin metal ground is treated as a dielectric layer with complex permittivity. Numerical results show that, when the inside metal ground is very thin, an electromagnetic field can penetrate it and interact with layers underneath. Additionally the metal layer has a great impact on the propagation phase constant even when thickness is much less than the skin depth. And the microstrip lines with the thin metal ground in both lossy and lossless substrates excite a slow wave.