The generation of electromagnetic radiation from the unstable electrostatic waves of a beam–plasma system is investigated by means of computer simulation. A two‐dimensional model is employed in which the plasma is treated as a finite system and in which the effects of a continuous beam inflow are included. For the parameters of the simulation (nb/n0∼1%, an essentially nonrelativistic beam, and no external magnetic field), the radiation is concentrated near the plasma frequency, is emitted preferentially perpendicular to the beam, and is polarized withEparallel to the beam direction. Radiation at the second harmonic is found to be weak. The production mechanism is found to be the scattering of Langmuir waves from ion‐acoustic fluctuations, and the observed radiation level agrees well with the theoretical predictions for such a three‐wave coupling. The results of the numerical experiments are compared with the recent laboratory experiment of Whelan and Stenzel [Phys. Rev. Lett.47, 95 (1981)].