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The important EMC problem of a high-frequency electromagnetic field coupling to a single-conductor transmission line of finite length is considered. In particular, a general method to determine the current induced on the line subjected to a generic incident field wave is proposed. The governing integro-differential equation of the problem is solved by means of a numerical procedure based on a Fourier series transformation. It can be proved that the series in which the unknown of the problem, namely the current along the line, is developed converges to the exact solution and only few terms are needed. The proposed approach represents a more accurate alternative to the transmission line (TL) approximation, since it allows the removal of its typical limitations, namely assumptions about the absence of a common mode current and about the TEM (or quasi-TEM) propagation mode. Such assumptions determine restrictions on the maximum value of line height and width with respect both to the line length and to the minimum field wavelength. Numerical results obtained on a test line excited by a suitable electromagnetic pulse are compared with those provided by the numerical electromagnetic code (NEC) and a good agreement is highlighted.