1. Field of the Invention
This invention relates to antennas employing single reflector configurations and, more particularly, to antennas of this character adapted for use simultaneously for a plurality of frequency bands, with the multiple main beams (at different frequencies) coincident, separate or scannable.
2. Description of the Prior Art
It has been proposed in the prior art, for coincident multiple beams, to use a single reflector for a pair of frequency bands from a pair of feeds. This has been achieved by employing dicroic frequency selective surfaces. Prior art systems of this type are disclosed, for example, in T. W. Leonard and L. R. Young, "Frequency Selective Surfaces," AP-S International Symposium, June 1977, pp. 560-563 and A. G. Cha, "Beam Squint in Large Ground Station Antennas," AP-S International Symposium, June 1977, pp. 538-540. Such frequency selective surfaces, however, require high manufacturing tolerances and employ multilayers which increase the losses and cost of the antennas.
Separate multiple beams, however, are generated from multiple separate feeds at the focal area of the reflector. These are restricted to minimum beam separation which corresponds to the sizes of the feeding arrangements. The degradation of the beams is a function of the beam separation and the multiplicity of the feeding arrangements. Detailed description of these systems are disclosed, in M. Afifi and P. Foldes, "Optimum Contiguous Multibeam Antenna Coverage," AP-S International Symposium, June 1980, pp. 74-77.