Showing papers on "Beamforming published in 1970"

Adaptive beamformer with beam mainlobe maintenance

Abstract: An adaptive beamformer and signal processor for sonar and other signal receptor arrays, in which beamforming is accomplished by correlation feedback loops providing matched weighting across the array. To constrain the adaptive beamformer thus comprised against cancellation of useful signals from a particular angular region, which normally is the beam mainlobe or boresight region, one or more spatial notch filters are interposed within the correlation feedback loops for preventing signal suppression within such angular region.

A class of phase-interpolation circuits for scanning phased arrays

Abstract: A class of circuits is described that can be used with a phased-array antenna in order to allow a given array feed system to provide phase control for a phased array with many more elements Alternatively, certain variations of these circuits can be used alone to provide phase control for small arrays while using only a single phase shifter for each direction of scan

Beamforming in highly reverberant wind tunnels possibilities and limitations

Abstract: Closed-section hard-walled wind tunnels are routinely used for aerodynamic testing during the early stages of vehicle design. The use of microphone arrays and beamforming processing in such environments can yield useful source localisation information; yet there are concerns as to the consistency of quantitative results from such methods when compared to anechoic openjet tunnel testing. Higher background noise levels, microphones in contact with the turbulent boundary layer, and the highly reverberant nature of the measuring environment are of particular concern. In this paper we show that accurate results in closed-section wind tunnels are still possible using the cross-spectral matrix diagonal removal (DR) technique, and with dereverberation. With DR, improvements in beamformer’s accuracy up to 10 dB can be achieved when compared to standard beamforming. De-reverberation gives an additional 10 dB improvement, and provided that the noise contamination to the microphone pressure data is somewhat suppressed, errors within §1dB can be expected. Both of these methods do not require any additional changes to the physical infrastructure of the measuring environment.

Processing partially coherent large seismic array for discrimination

Abstract: Seismic signals in a band of frequencies near 1.0 Hz. can be detected from underground explosions and earthquakes at distances of several thousand kilometers. A stochastic model has been proposed to characterize observed signal variations within a Large Aperture Seismic Array (LASA). The model assumes that the observed signal spectrum at a seismometer is some average spectrum multiplied by a random gain and phase. Within a subarray (7 km. aperture) the mean value of the modulus squared of the random term is approximated by 1.0 +0.18 f2 where f is frequency in Hz. For sensors drawn from the full LASA (200 km. aperture) the value is 1.0 +2.0 f2. Two alternative methods for extracting spectral information above 1.0 Hz for discrimination between event types are compared. Beamforming spectra are obtained from the Fourier transform of the average received signal. An alternative incoherent processing method, spectraforming, is to calculate the average spectrum from individual seismometers. Both can be corrected for bias. It is demonstrated that although beamforming will give more noise rejection than spectraforming, that the latter can be superior in terms of output signal to noise ratio when input signal variations between sensors are large. Spectraforming may be of significant value for obtaining spectral information in the 1.0 - 3.0 Hz band for events with Richter magnitudes in the range 4.0 - 4.5. This magnitude range is of considerable current interest for the purpose of nuclear test detection and discrimination.

Very wide-band phased arrays

Abstract: A phased array is described that has been matched to operate over nearly an octave. A method of achieving very wide bandwidth with phased arrays integrated with transistors is suggested.

APPA: A Phased Array System Designed for Space Application

Abstract: Artificial pilot phased array (APPA) is a system designed for application as a multiple narrow-beam communication satellite. The design uses an adaptive array principle in a multiple-beam configuration. Two ground pilot signals are used to make beam steering independent of array attitude. Beam steering is accomplished without the requirement of user pilots by deriving array phase shifter settings from user locations. The system's principle of operation is persented along with a description of a laboratory model and a design application to a data relay satellite.

Reflection-lobe dispersion in a phased-array antenna

Abstract: Reflection lobes in phase-scanned arrays with traveling-wave feeds can significantly degrade sidelobe levels. These lobes can be dispersed if the regularity of the feed system can be destroyed. In this communication, an aperture phase distribution is described that provides the maximum reflection-lobe dispersion for an arbitrary reasonably smooth amplitude distribution. This phase distribution is an explicit function of the amplitude distribution. The theoretical limitations on reflection-lobe dispersion in one- and two-dimensional arrays are determined and compared with the calculated properties of a sample linear array. The edge effects are also indicated.