The present work deals with the problem of the diffraction of electromagnetic waves by knife-edge obstacles with arbitrary transverse profile. From the Huygens-Fresnel (acalar formulation) and the Stratton-Chu ( vectorial formulation) integrals, a closed-form solution for the problem is establications. The theoretical results are verified by comparison with experimental measurements fot three kinds od profiles: semi-circular, triangular and ramp. Using this same formulation, the behavior of the field behind the obstacle is investigated, where a region of interference exists caused by the several independet contributions of the diffracted field. An attempt was made to interpret the final results in terms of the first Fresnel zone radius in cases of triangular and ramp obstacles. Although the model used here is limited for not taking into account the longitudinal dimension of the obstacles, the obtained conclusions have major importance to radio links operating in diffraction.