1. Field of the Invention
The invention relates to a sidelobe canceller system for cancelling multiple interference signals from the sidelobes of the main antenna of a communications receiver. More particularly, the invention relates to the use of directional auxiliary antennas and time delays to allow the spacing between the auxiliary antennas and the main antenna to be increased.
2. Description of the Prior Art
A communications receiver has a main antenna and may have a sidelobe canceller system for cancelling interference from the sidelobes of the main antenna. Prior art side lobe canceller systems normally contain multiple auxiliary antennas which may be either directional (U.S. Pat. No. 3,177,489) or omnidirectional and are spaced close to the main radar antenna. The spacing is critical because the signals from the main radar antenna and from the auxiliary antenna must be received in the adaptive-loop canceller at the same time for autocorrelation and cancelling to take place. The spacing is dependent on the radar pulse-width and is of the order of 1/100 of the distance light will travel in the time-equivalent of the pulse-length, normally several meters (i.e., 3 meters for a 1 .mu.sec. pulsewidth). Such systems have trouble cancelling multiple interference signals which have only a small difference in angle of arrival. It would be desirable to have a system in which the main and auxiliary antennas could be widely spaced (e.g., 150 meters) to obtain good angular resolution of interference signals but still have the main and auxiliary antenna signals received simultaneously at the adaptive loop canceller system so that autocorrelation and cancelling would take place.