New empirical unified dispersion model for shielded-, suspended-, and composite-substrate microstrip line for microwave and mm-wave applications

By introducing the concept of "virtual relative permittivity," this paper reports several closed-form dispersion models for a multilayered shielded/unshielded microstrip line over 1<ε/sub r/⩽20, 0.1⩽(w/h)⩽10, (h/sub 3//h)⩾2 in the frequency range up to 4 GHz.cm. The maximum deviation of the one model against the results of the spectral-domain analysis (SDA) is limited to 3%, while for the other three models, the maximum deviation is <2% and the root-mean-square (rms) deviation is <0.8%. This paper also reports improvement in the closed-form model of March for the determination of ε/sub eff/(O) of the shielded microstrip line.