Several experiments have evidenced oscillatory patterns of the electrostatic potential radiated by a small antenna in a hot magnetoplasma. Several previous interpretations based on analytical calculations and numerical computations are discussed; they are found not to be exhaustive or completely satisfactory. A new mechanism responsible for these structures is proposed. It consists of a filtering by the plasma of the wave vectors of the radiated waves. This mechanism is caused by the existence of a restricted range of undamped wave vectors surrounded by highly damped ones. This phenomenon, presently named ‘‘intrinsic diffraction,’’ is used to interpret both the spatial oscillations of the potential around the resonance cone when ω<min(ωp, ωc) and around the direction perpendicular to the magnetostatic field when nωc<ω<(n+1)ωc; ω, ωp, ωc are, respectively, the wave, the plasma, and the electron-cyclotron frequencies, and n is any positive integer. The results of both analytical calculations and numerical computations are found to be in good agreement within the two frequency ranges. The location and the amplitude of the oscillatory structure are simply related to the width of the domain of unattenuated wave vectors. New diagnosis methods for the plasma temperature are suggested from this model. Additional directivity and curvature effects related to the topology of the wavenumber surfaces are discussed. The generalization of the use of the intrinsic diffraction picture is proposed.