Control of surface currents by the use of channels

THE PRESENCE of radiation in the shadow zone of an antenna depends upon surface currents that flow away from the optically lighted region. Minimizing this shadow illumination requires control of these surface currents. For example, even with a large cylinder (circumference =40λ) excited by an infinite axial slot, the shadow zone of the theoretical pattern has maxima 90° from the slot which are down only 3 db, and others 180° away only 28 db below the power level at 0°. This paper is an experimental study of methods of controllino: shadow zone illumination.