Determination of antenna reactance from the far-field expressions

Using the Hilbert transform, a simple expression is derived for the reactance of a dipole antenna in terms of the radiation resistance which is assumed known. Since the radiation resistance can be found from the far-field equations (i.e., Fourier transform of the antenna current distribution), it is shown that it is not necessary to determine the near field to obtain the antenna reactance. Numerical results are in excellent agreement with those available in the literature.