Radiation patterns of circular apertures with structural shadows

The shadows and blockage occurring in large antennas are approximated to by well-defined regions constructed from radii and arcs of circles, which are concentric with the aperture, projected onto the aperture plane. The radiation patterns of the obstructed aperture are obtained for both uniform and tapered illumination from the scalar integral. It is shown that apertures obstructed by four symmetrically placed shadows suffer comparatively little degradation, but that three symmetrically placed shadows give a considerable increase in the beamwidth in any plane that contains a shadow region.