Lower-bound algorithms for coplanar line and gap capacitance evaluations

Coplanar line characteristics have been widely investigated. However, calculations of capacitances, both in air and in inhomogeneous dielectric, have often been based on simple yet successful assumptions, which seem to deserve further validation. In this paper, both non conventional conformal mapping techniques and a new variational formulation are used, leading to accurate upper-bound impedance evaluations, and some comparisons with lower-bound results and published data are presented. Moreover, the application of refined variational algorithms to gap capacitance evaluations is discussed: the algorithm proposed by Maeda (1972) for computation of gap capacitances is revisited, and some improvements are described. Results are discussed with reference to values already presented in the literature and excellent agreement with experimental data is shown