Tests of microstrip dispersion formulas

A set of published formulas for the frequency dependence of the microstrip effective relative dielectric constant ε_re( f) is tested relative to an assemblage of measured data values for this quantity chosen from the literature. The RMS deviation of the predicted data obtained from the measured values ranged from 2.3% to 4.1% of the seven formulas for ε_re(f) tested. A formula due to M. Kirschning and R.H. Jansen (see Electron. Lett., vol.18, p.272-73, 1982) showed the lowest average deviation from measured values, although the differences between the predictions of their formula and others tested are of the order of the error limits of the comparison process. It is concluded that the results indicate the suitability of relatively simple analytical expressions for the computation for microstrip dispersion