Pattern limitations in multiple-beam antennas

It is shown that in a lossless passive antenna radiating multiple beams from a common aperture, the radiation pattern and the crossover levels cannot be specified independently. This is due to a requirement that the beams must be orthogonal in space. It is also shown that this limitation can be overcome by using multiple apertures, lossy networks, or active networks. Suitable arrangements for obtaining low sidelobes with satisfactory crossover levels are described.