The effect of interference extent on LMS spatial cancellation

The LMS canceller structure has been widely used to spatially reject strong interferences from the output of a sonar array. It has generally been assumed that each interference consists of a single plane wave arrival. In some applications, the interference may actually have angular extent which can dramatically influence canceller performance. This paper demonstrates these effects for a bandlimited, spectrally flat interference by means of a computer simulation. Cancellation achieved is determined as a function of source extent, reference hydrophone spacing, and distance between the references and primary. These results are compared to previous results obtained at a single frequency. It is shown that for a well designed canceller, the single frequency results at an effective frequency, fe, predict performance with the broadband interference. This allows a number of design guidelines and closed form approximations developed at a single frequency to be used in the more realistic broadband case.