An empirical formula for the frequency-dependent effective permittivity of a shielded microstrip line

With the concept of a virtual substrate, a closed-form dispersion model, ϵeff(f), for a shielded microstrip line is presented with a maximum error of 3.63% and an average error within 2% for 0.6 ≤ W/h1 ≤ 10, 1 ≤ ϵr1 ≤ 20, 0 ≤ f ≤ 100 GHz, h2/h1 ≥ 2. The model is suitable for the CAD of shielded microstrip structures. © 1996 John Wiley & Sons, Inc.