Sum and difference pattern with common aperture tail

For tracking and search design array antennas is very usually the optimization of the main beam sum pattern to sidelobe level ratio, SLL, while still maintaining high directivity of the main beam. For tracking systems, a difference pattern is needed as an auxiliary pattern with a boresight null coincident with the beam peak of the main (sum) pattern. The tracking drive system moves the antenna positioner until the signal in this difference channel reaches a minimum, thereby causing the main channel (sum) to point accurately at the radar target. Aperture distributions of sum good patterns, e. g. Taylor distributions, and difference patterns, e. g. Bayliss distributions, are different. Theoretically, two independent excitations could be applied to the search-and-track antenna in order to achieve good features in both patterns. However, this approach requires a feed network too complex to make a practical design feasible.