Diffraction by cylindrical reflectors

The electromagnetic diffraction problem is formulated in terms of the determination of the currents induced on a refiector-scatterer by a primary source. All field quantities are readily determined therefrom. An approximate solution ignores the interaction of currents on the refiector-scatterer in that it relates the surface current to the incident magnetic field. This is the geometrical-optics current. For the strip and circular reflector with line source at its centre, corrections to the geometrical-optics currents are obtained by an approximate analytic technique. In each case this yields an equivalent line current at the edges. The field of the line current is non-isotropic; its directional gain is determined by appealing to the Sommerfeld half-plane solution. The line currents do not greatly affect the total pattern; this indicates that the main character of the diffraction can be obtained from the geometrical-optics currents. Measurements of the diffracted field of a circular cylindrical reflector with line feed at its centre were made in a parallel-plane device. A description of some of the features of the equipment is given. The results confirm that geometrical-optics currents are themselves satisfactory, but are inconclusive with respect to the correction line currents.