Design formula for a printed disc capacitor

An established formula for capacitance C of a thin metal disc printed on a dielectric substrate with height h and relative permittivity er >= 2.2, backed by a conducting ground plane, is inverted into a closed formula. The latter yields disc's radius r for a given C and a given substrate, with an accuracy of 5 % of C or better if r >= h/2. It will save the design engineer time, whose alternative is to resort to a numerical field solver and go by trial and error. O 2017 Elsevier Inc. All rights reserved.