Showing papers on "Adaptive beamformer published in 1967"
TL;DR: The techniques described in this paper are applicable to signal‐receiving arrays for use over a wide range of frequencies and substantial reductions in noise reception are demonstrated in computer‐simulated experiments.
Abstract: A system consisting of an antenna array and an adaptive processor can perform filtering in both the space and frequency domains, thus reducing the sensitivity of the signal‐receiving system to interfering directional noise sources. Variable weights of a signal processor can be automatically adjusted by a simple adaptive technique based on the least‐mean‐squares (LMS) algorithm. During the adaptive process an injected pilot signal simulates a received signal from a desired “look” direction. This allows the array to be “trained” so that its directivity pattern has a main lobe in the previously specified look direction. At the same time, the array processing system can reject any incident noises, whose directions of propagation are different from the desired look direction, by forming appropriate nulls in the antenna directivity pattern. The array adapts itself to form a main lobe, with its direction and bandwidth determined by the pilot signal, and to reject signals or noises occurring outside the main lobe as well as possible in the minimum mean‐square error sense. Several examples illustrate the convergence of the LMS adaptation procedure to the corresponding Wiener‐optimum solutions. Rates of adaptation and misadjustments of the solutions are predicted theoretically and checked experimentally. Substantial reductions in noise reception are demonstrated in computer‐simulated experiments. The techniques described in this paper are applicable to signal‐receiving arrays for use over a wide range of frequencies.
811 citations
01 Jan 1967
TL;DR: It is shown that although the system initially cannot discriminate between the target and the interference, it eventually acts to eliminate the effect of the interference almost completely and how the useful signal to noise ratio increases during adaptation.
Abstract: : This paper deals with the design and analysis of an adaptive array processor for use in passive detection of directional stochastic signals such as are found in sonar. The processor consists of a set of tapped delay-line filters, one for each array element. The algorithm used for adjusting the tap gains is a modification of the stochastic approximation method of Robbins and Monro, and it utilizes knowledge of the signal autocorrelation function and spatial direction of the target. It is shown that the final form approached by the processor is that of a space-time filter optimized in the direction corresponding to assumed target location. The system performance is analyzed by considering a noise field consisting of a spatially isotropic component and a single directional component referred to as an interference. It is shown that although the system initially cannot discriminate between the target and the interference, it eventually acts to eliminate the effect of the interference almost completely. It is also shown how the useful signal to noise ratio increases during adaptation. (Author)
2 citations