Mainlobe canceller with motion compensation for use with radar systems

Abstract

This invention relates to a mainlobe jamming cancellation system which cane used to allow a radar to detect targets even when relative motion exists between the jammer and the radar platform. In particular, this invention relates to a mainlobe canceller that utilizes a main antenna and one or more widely spaced auxiliary antennas in conjunction with one or more phase locked loops (PLL), to automatically align the jamming signals received by the several antennas. The alignment is necessary to realize a high degree of jammer cancellation.

We claim: 
     
       1. A mainlobe jamming cancellation system for removing mainlobe interference signals in radar systems when relative motion exists between the sources of said interference signals and the receiving antennas, comprising: (a) a main antenna for broadcasting and receiving radio signals;   (b) at least one auxiliary antenna spaced from said main antenna for receiving said interfering signals;   (c) means for multiplying, weighting, and summing said interference signals received by said at least one auxiliary antenna;   (d) means for aligning the frequencies of said multiplied and weighted signals with the frequency of the radio signals received by said main antenna;   (e) means for time-aligning the signals received by said main and auxiliary antennas;   (f) canceller means for subtracting said time-aligned signals from said signals received by said main antenna; and   (g) receiver means for receiving the residue of said main antenna signals for detecting a target.   
     
     
       2. A mainlobe jamming cancellation system as set forth in claim 1, wherein said means for aligning the frequencies comprises a phase locked loop circuit for aligning the frequencies of the signals received from said main and auxiliary antennas, in series with a canceller. 
     
     
       3. A mainlobe jamming cancellation system as set forth in claim 1, wherein said means for aligning the frequencies comprises a phase locked loop circuit intergrated with the circuitry of a canceller for extracting phase information needed to align said frequencies from a weight computed by said canceller. 
     
     
       4. A mainlobe jamming cancellation system as set forth in claim 3, which includes a plurality of auxiliary antennas, each of which has a phase locked loop circuit for frequency alignment integrated with the circuitry of its own canceller and its own weighting circuit for cancelling multiple mainlobe jamming signals. 
     
     
       5. A mainlobe jamming cancellation system as set forth in claim 3, which includes an adaptive transversal filter for automatic time alignment of wideband jamming signals wherein phase information is extracted from a subset of adaptively computed tapweights to perform frequency alignment for motion compensation.