Estimation of the characteristic impedance of a transmission line by variational methods

A large number of field problems cannot be solved exactly. Instead, an approximate solution is obtained by computation. The object of the paper is to draw attention to a method which gives an upper and a lower bound for the exact solution. The method, based on the fact that the basic equations of electromagnetism can be derived from a variational principle, is applicable to a variety of problems having a rather complicated geometry. The effectiveness of the method is illustrated by two characteristic examples.