A planar current is generally divided into a radiating part that generates propagation fields and a non-radiating part that generates evanescent fields. This paper proposes a direct method to reconstruct the radiating part of a planar source from its far fields based on their exact relationship. A standard reconstruction process is provided in which the far-fields are sampled at the peaks of each propagation mode. Analysis shows that the achievable reconstruction resolution of the source distribution is about half a wavelength. The paper also demonstrates that it is possible to reconstruct the source by sampling the far-fields on a plane or along a linear path. The performance of the reconstruction algorithm is illustrated with numerical examples.