Irregularly shaped patch as perturbation of regularly shaped patch

A rapid and accurate approach for the solution of an irregularly shaped patch from a regularly shaped patch is based on the observation that the former patch can usually be taken as a perturbation of the latter. The latter has fast convergence and accurate modal solution; its perturbation being small, both in physical size and in changes from the modal solution, is easy to derive with electrostatics and can tolerate computational error.