I. Introduction
THE mutual inductance calculation between coaxial circular filaments has been thoroughly treated by a number of authors since the time of Maxwell, and an accuracy exceeding anything required in practice is nowadays possible [1]–[7]. A formula for two circles whose axes intersect was first given by Maxwell [1]. Formulas for circular loops with parallel axes have later been derived by Butterworth [2] and Snow [5]. Unfortunately, these formulas are slowly convergent and are applicable only within a restricted range of parameters. Using Butterworth's formula [2], Grover developed a general method to calculate the mutual inductance of inclined circular filaments in any desired positions in the form of a single integral [3], [4].