Array processing involves manipulation of signals induced on various antenna elements. Its capabilities of steering nulls to reduce cochannel interferences and pointing independent beams toward various mobiles, as well as its ability to provide estimates of directions of radiating sources, make it attractive to a mobile communications system designer. Array processing is expected to play an important role in fulfilling the increased demands of various mobile communications services. Part I of this paper showed how an array could be utilized in different configurations to improve the performance of mobile communications systems, with references to various studies where feasibility of apt array system for mobile communications is considered. This paper provides a comprehensive and detailed treatment of different beam-forming schemes, adaptive algorithms to adjust the required weighting on antennas, direction-of-arrival estimation methods-including their performance comparison-and effects of errors on the performance of an array system, as well as schemes to alleviate them. This paper brings together almost all aspects of array signal processing.

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Application of antenna arrays to mobile communications. II. Beam-forming and direction-of-arrival considerations

A portable ultrasound imaging system includes a scan head coupled by a cable to a portable battery-powered data processor and display unit. The scan head enclosure houses an array of ultrasonic transducers and the circuitry associated therewith, including pulse synchronizer circuitry used in the transmit mode for transmission of ultrasonic pulses and beam forming circuitry used in the receive mode to dynamically focus reflected ultrasonic signals returning from the region of interest being imaged.

Portable ultrasound imaging system

A method and apparatus are provided for imaging an object using a transducer array for transmitting one or more beams that are steered and/or translated to transmit scan lines for multiple excitation events so as to scan a field of view of the object, for sensing received signals reflected from the object after each excitation event on one or more receive beams on receive scan lines, and for transducing those sensed received signals into corresponding electrical signals. The method and apparatus is additionally for acquiring and storing coherent samples retaining both phase and amplitude information of those electrical signals obtained on the receive scan lines throughout at least a portion of the field of view, and for combining stored coherent samples associated with distinct receive beams to synthesize new coherent image samples aligned on synthetic scan lines which are distinct from any one of (1) receive scan lines on which a signal was sensed, (2) transmit scan lines on which a signal was directed, or (3) transmit scan lines and receive scan lines. The method and apparatus is further for detecting the synthesized coherent image samples and displaying or recording the resulting image field.

Method and apparatus for coherent image formation

Time domain and frequency domain concepts which aid in the design and efficient implementation of a digital beamformer have been described at various times in the literature. The numerous beam-former structures that result are discussed with an emphasis on hardware requirements and spectral areas of application. Time domain procedures which include delay-sum, partial-sum, interpolation and shifted-sideband beamforming, and frequency domain techniques which include the application of discrete Fourier transforms and phase shift beam-forming are considered. Hardware considerations are primarily in the areas of analog-to-digital conversion, data storage, and computational throughput requirements.

A comparison of efficient beamforming algorithms

The present invention includes a fully programmable plurality of multi-channel receivers, each receiver having a digital multi-channel receive processor and a local processor control. Each receive processor includes a first decimator, time delay memory, second decimator, and complex multiplier. The receive beamformer is a computationally efficient system which is programmable to allow processing mode trade-offs among receive frequency, receive spatial range resolution, and number of simultaneous beams received. Each local control receives focusing data from a central control computer and provides final calculation of per-channel dynamic focus delay, phase, apodization, and calibration values for each receiver signal sample. Further, this invention includes a baseband multi-beam processor which has a phase aligner and a baseband filter for making post-beamformation coherent phase adjustments and signal shaping, respectively. The phase aligner maintains scan-line-to-scan-line coherency, such as would be required for coherent image formation. Accordingly, the present system can operate under multiple imaging formats, using a variety of transducers and a variety of modes such as B-mode, M-mode, and color Doppler flow mode.

Method and apparatus for receive beamformer system

For many sonar applications, the sensor outputs of a hydrophone array are sampled at a rate significantly higher than that required for waveform reconstruction when digital beamforming is used. The reason for this is that the number of synchronous, or ’’natural,’’ beampointing directions is proportional to the beamformer input rate. This paper presents an implementation of a digital beamformer that achieves the desired synchronous beams while minimizing the sensor channel sampling rate requirement. The technique employs zero padding of sensor data followed by digital interpolation filters to achieve vernier beamformer delays. Interpolation filtering can be done either at the beamformer input or output to minimize processing requirements. The resulting structure realizes a hardware savings since both A/D converter and cable bandwith requirements can be traded off against digital processing complexity to achieve an optimal partitioning.

A novel approach to digital beamforming

A beamformer for an array of sonar transducers, or electromagnetic radiating elements, includes mixers for translating the signals received by the transducers to a lower frequency. The beamformer incorporates delay lines operating at a clock rate which is reduced in proportion to the decrease in frequency. Each delay line provides delays to the signals of corresponding ones of the transducers in accordance with the time of arrival of a wavefront of radiation upon the respective transducers. Phase shifters coupled between the mixers and the delay lines impart phase shifts to the transducer signals proportional to the respective delays to compensate for the lowering of the frequency.

Beamformer with reduced sampling rate

Sonar ice thickness measurement comprises transmitting an AM and subsequent CW sonic radiant energy signals (13,30) from a high frequency sonar transducer (11) in the water (12) toward the sonic signal reflecting ice cap (19). Reflection (30ʹ) of the CW signal (30) from the water-ice interface (18) and reflection (15ʹ) from the water-air interface (16) of the modulating frequency (15), generated by non-linear of parametric effects in the water (12) by the modulated transmit signal (13), causes the CW signal (30) to be modulated to generate side bands at the modulating frequency on each side of the carrier frequency to provide an FM high frequency signal (27), received by the transducer (11). Detection of the FM signal (27) determines the time of arrival of the echo of said detected FM signal (27) relative to the detection of the reflected modulated signal (14) from the water-ice interface (18). The time difference (TT) between the detected signals (14ʹ,27ʹ) and an assumed value of the speed (CICE) of sound through the ice (19) give the thickness (D) of the ice cap (19).

System and method for measuring ice thickness

A system for the determination of the direction of a source of sound in water utilizing the finite amplitude effect. A narrow beam of sonic energy at a frequency higher than that of the source is projected in a direction opposite the direction of the source. A hydrophone receiving beam intercepts the projector beam at a distance from the projector thereof, the distance being sufficient to permit a finite amplitude non-linear interaction of the projector beam energy and the energy of the source via a virtual end-fire array. Cross-modulation products resulting from the non-linear interaction are received by the hydrophone, the precision of measurement being dependent on the directivity pattern of the virtual end-fire array.

Sonic direction system

For many applications, digital beamformers require an input rate which is significantly higher than that required for waveform reconstruction to achieve an adequate set of synchronous beams. Typically, this high rate is realized in the A/D conversion of the sensor outputs. A novel alternative, discussed in this paper, is to sample the sensors at a rate consistent with the Nyquist criterion and implement vernier beamformer delays by digital interpolation. This technique, which is referred to as digital interpolation beamforming, permits an efficient partitioning between A/D converter and cable bandwidth requirements and digital processing complexity. The basic structure of an interpolation beamformer is presented. It is shown that interpolation filtering and beamforming can be interchanged to minimize digital processing. Beam‐pattern degradation due to interpolation error is derived and interpreted for the special case of a line array.

Roger G. Pridham

Papers

A novel approach to digital beamforming

Beamformer with reduced sampling rate

System and method for measuring ice thickness

Sonic direction system

Digital interpolation beamforming; concept and theory