Showing papers on "Phased array published in 1997"

Theory and application of array coils in MR spectroscopy

Abstract: The theory and application of array coils are reviewed in the context of phased array spectroscopy. The optimization of the signal-to-noise ratio from an array of coils is developed by considering the efficiency of a phased array transmit coil. This approach avoids the need to consider noise correlation, and should be useful in future considerations of transmit phased array coils for MR spectroscopy. Methods to characterize array coil performance, including fields and coupling are briefly summarized, along with methods to minimize the effects of mutual inductance. The signal-to-noise advantages of array coils over single coils are examined for both planar and cylindrical arrays. Numerical simulations of planar arrays of 2×2, 4×4 and 8×8 elements and constant overall dimension are compared to a single coil of the same size. The results demonstrate a significant improvement in sensitivity near the array coil. Although the benefits of the array decrease as a function of distance from the array, the array sensitivity never drops below that of a single coil with the same overall dimensions, or that of a single element of the array. Similar results are obtained for a sixteen element cylindrical array, which is compared to a standard quadrature birdcage coil using both computational methods and phantom measurements. The phased array techniques reviewed are demonstrated with proton spectroscopic images of the brain. © 1997 John Wiley & Sons, Ltd.

Photonic beamformer for phased array antennas using a fiber grating prism

Abstract: This letter presents, for the first time, measured data on a Bragg reflection grating based fiber-optic prism true time delay processor for transmit/receive phased array beamforming. Measurements taken over a 3.5-GHz bandwidth demonstrates high resolution beamsteering and highly linear low-noise phase data. The system takes maximum advantage of component reuse and fully integrates the transmit and receive modes in one efficient hardware compressive topology.

Novel ferroelectric materials for phased array antennas

Abstract: Various composites of barium strontium titanium oxide (BSTO) combined with other nonelectrically active oxide ceramics have been formulated for application in phased array antennas. In general, the composites have adjustable electronic properties which can be tailored for use in phased array antennas and other phase shifting devices. The dielectric constant and the loss tangents have been reduced to enhance the overall impedance matching and thereby lowering the insertion loss of the device. In addition, the overall tunability, the change in the dielectric constant with applied voltage, is maintained at a sufficiently high level. In order to address a broad frequency range in the microwave region, the composites have been fabricated in bulk ceramic, thick film, and thin film form. This article discusses the processing, material characterization, and electronic properties of the composites in MHz and GHz frequencies.

Mobile underwater arrays

Abstract: An oceanographic sampling system includes two or more underwater vehicles disposed in an array and an array controller for controlling the array of underwater vehicles as data is acquired. Each underwater vehicle includes a propulsion system for moving the underwater vehicle independently of the other underwater vehicles, a sensor for sensing an ocean parameter and providing sensor data representative of the ocean parameter as the underwater vehicle moves, a navigation subsystem for determining position data representative of the position of the underwater vehicle as the sensor data is acquired and a synchronizing subsystem for time synchronizing the sensor data and the position data acquired by the underwater vehicle with sensor data and position data acquired by other underwater vehicles. The array of underwater vehicles may function as a large aperture phased array, and phased array analysis techniques may be applied to the time-synchronized sensor data and position data.

Continuously variable true time-delay optical feeder for phased-array antenna employing chirped fiber grating

Abstract: In this paper, we present and demonstrate a novel approach of a true time-delay (TTD) optical feeder for phased-array antennas (PAAs). A continuously variable TTD is achieved by employing tunable lasers and a wide-bandwidth chirped fiber Bragg grating (FBG) as the dispersive element. The results show that a very high resolution performance (equivalent to a 6-b microwave phase shifter) is obtained for an L-band PAA employing narrow-tuning bandwidth lasers with a wavelength stability of 0.005 nm and a 4-nm bandwidth chirped grating with a dispersion of 835 ps/nm.

Synthetic phased arrays for intraluminal imaging of coronary arteries

Abstract: A 64-element, high efficiency, ceramic piezoelectric array transducer operating at 20 MHz has been constructed for ultrasonic intraluminal imaging. The array is mounted on the surface of a 1.2 mm diameter catheter appropriate for coronary artery applications. Integrated into the catheter tip is a custom analog chip set permitting complete data capture from the array. That is, on each firing any combination of array elements can be selected independently as transmitter or receiver. Using data acquired in this way, a complete phased array aperture (i.e., independent transmit and receive apertures) can be synthesized. Reconstruction hardware based on a custom application specific integrated circuit (ASIC) has been designed and built to produce real-time images. Beam forming coefficients are derived using an optimal filtering approach accounting for the circular geometry of the array. Simulated and measured beam patterns for this system are compared. In addition, images of coronary anatomy acquired with the real-time system are displayed demonstrating the marked image quality improvement compared to previous synthetic aperture intraluminal systems.

Elevation performance of 1.25D and 1.5D transducer arrays

Abstract: Present 1D phased array probes have outstanding lateral and axial resolution, but their elevation performance is determined by a fixed aperture focused at a fixed range. Multi-row array transducers can provide significantly improved elevation performance in return for "modest" increases in probe and system complexity. Time domain simulations of elevation beam profiles are used to compare several types of multi-row probes. The elevation aperture of a 1.25D probe increases with range, but the elevation focusing of that aperture is static and determined principally by a mechanical lens with a fixed focus (or foci). 1.25D probes can provide substantially better near- and far-field slice thickness performance than 1D probes and require no additional system beamformer channels. 1.5D, probes use additional beamformer channels to provide dynamic focusing and apodization in elevation. 1.5D probes can provide detail resolution comparable to, and contrast resolution substantially better than, 1.25D probes, particularly in the mid- and far-field. Further increases in system channel count allow the use of 1.75D and 2D arrays for adaptive acoustics and two-dimensional beam steering. Significant improvements in clinical image quality can be expected as multi-row probes become increasingly available in the marketplace.

True time-delay scheme for feeding optically controlled phased-array antennas using chirped-fiber gratings

Abstract: A novel approach of true-time delay (TTD) optical feeder for phased-array antennas is proposed and demonstrated. A compact size continuously variable TTD is achieved by employing tunable lasers and one wide bandwidth chirped-fiber grating as dispersive element. A high-resolution performance (5.3 ps) is obtained for a 26-GHz phased-array antenna employing narrow tuning bandwidth lasers with a wavelength stability of 0.005 nm and a 4 nm bandwidth chirped grating.

Phased array-based systems and applications

Abstract: Phased Array--Based Systems and Applications. From Filled Apertures to Phased Arrays Mounted on Fully Steerable Structures. Phased Arrays: Canonical and Wideband. Transmit/Receive Modules. Antenna Elements. References. Index.

The combined concentric-ring and sector-vortex phased array for MRI guided ultrasound surgery

Abstract: MRI guided ultrasound surgery requires small surgical equipment volumes to facilitate the treatment of larger patients in the limited space of a conventional MRI magnet. In addition, large focal volumes are required to reduce the treatment time of large tumors. The concentric-ring array is capable of moving the focus in one dimension, and previous studies have shown that a circular array composed of radial sectors is capable of producing enlarged focal volumes. These two array designs may be combined to create an array that is capable of both enlarging the focus and moving the focus along the axis of the array. Simulations were performed to predict the performance and capabilities of various combined array designs by using numerical routines to, calculate the acoustic power field, temperature distribution, and accumulated thermal dose. The results shown predict that the combined array can create necrosed tissue volumes over 30 times larger than the concentric-ring array while maintaining focal range. The simulation results were verified with an experimental array consisting of 13 rings and 4 sectors. In addition, simulations were performed where multiple focal patterns were cycled in the time domain to create an optimized heating pattern characterized by uniform thermal dose over the volume of the lesion. Such heating patterns resulted in a 40/spl deg/C lower maximum temperature compared to single mode sonications while producing the same necrosed tissue volume, and yielded a rate of necrosis of 26.4 cm/sup 3//h.

Post-reception focusing in remote detection systems

Abstract: An apparatus is provided in which individual transmit elements (18) of a transmit array are actuated in turn in order to interrogate a search volume Signals reflected from the volume are received by one or more reception elements (20) of a receive array and are recorded The propagation parts to a selected cell are calculated and appropriate phase and or time shifts are inserted into the recorded data to simulate, post reception, the shifts that would have occurred if either or both of the transmit and receive arrays had been focused on the cell using phased array beam steering techniques

Design of phased-array wavelength division multiplexers using multimode interference couplers.

Abstract: Novel designs for phased-array wavelength-division multiplexers based on self-imaging properties of multimode interference (MMI) couplers are presented. These devices, which operate on N equally spaced wavelength channels, consist of two MMI couplers connected by an array of N monomode waveguides. The MMI couplers function as power splitters/combiners, and the waveguide array is the dispersive element. The excellent characteristics of MMI couplers offer the possibility of designing small-size devices with low loss and with high uniformity among different channels. A general theoretical formulation for an N-channel multiplexer is presented, and a simple procedure for finding an optimum set of lengths for the array guides is given. We show that these multiplexers can function as N x N wavelength-selective interconnecting components. The simulated performance of three variations of a five-channel device, designed in a rib waveguide system, is given. It is demonstrated that sidelobes in the multiplexer spectral response can be suppressed by weighting the power samples in the array waveguides through appropriate design of a nonuniform MMI power splitter.

Chirped fibre Bragg gratings for phased-array antennas

Abstract: A variable delay line for phased-array antennas based on a chirped fibre Bragg grating is demonstrated. The time delay of a microwave modulating signal is modified by scanning in wavelength a chirped grating. In this initial experiment, time delay variations up to 556 ps have been achieved using a grating of 0.4 nm bandwidth and 6 cm length and modulating in the frequency range 390 MHz-5.20 GHz.

Self-Focusing of Rayleigh Waves and Lamb Waves with a Linear Phased Array

Abstract: A simple idea for self-focusing of a linear array has been extended to Rayleigh and Lamb waves. The self-focusing procedure first measures the backscattered signals for a first transmission by a single element of the array. A cross-correlation technique is used to determine the time-of-flight differences of the backscattered signals received by the elements of the array. These time delays are used to adjust the times of excitation of the elements for transmission focusing on the defect. Using the differences in arrival time once more, the backscattered signals after transmission focusing are aligned for reception focusing. Experimental results demonstrate the ability to self-focus on single defects. For multiple defects, the technique has been extended to focus on the defect that produces the largest backscattered signal.

What is the optimum phased array coil design for cardiac and torso magnetic resonance

Abstract: To determine the optimum configuration of a phased array MR coil system for human cardiac applications, the sensitivity of 10 flexible array designs operating under ideal conditions was calculated at 13 points circling the myocardium of a model torso whose geometry was determined from healthy volunteers. The array geometries that were evaluated included continuous strips of 2, 4, 6, and 10 circular coils of diameter equal to half the torso thickness wrapped laterally around the torso, 2 pairs of coils located on the left side of the chest and back, clusters of 3 coils in 2 orientations, clusters of 4 and 6 coils, and a hybrid cross of 6 coils. The 4-, 6-, and 10-coil strip arrays out-performed the other designs for a given number of coils, yielding average theoretical sensitivity improvements of 45%, 53%, and 55% relative to a single flexible coil positioned at the point closest to the anterior myocardium, compared with about 30% for 4- and 6-coil clusters and the 2-pair geometry (P < 0.02). A flexible 4-coil strip array was constructed for a clinical 1.5 T scanner with 15-cm diameter circular surface coils on flexible circuit board. The signal-to-noise ratio (SNR) of this coil at the 13 cardiac locations was measured in 15 normal volunteers and compared with the SNR measured in images acquired with standard commercial MR coils: a body coil, a flexible torso array, a general purpose flexible coil, and, in 4 subjects, a dual array coil. In the prone orientation, the average myocardial SNR improvement of the 4-coil strip array was 650% relative to the whole body coil, compared with 310-340% for the other commercial coils (P < 0.00005). The twofold advantage over the commercial coils persisted in supine studies (P < 0.00005, n = 5). Thus, flexible circumferential phased arrays of strips of surface coils of diameter comparable with the depth of the heart generally out-perform many other standard geometries for a given number of coils, and can yield dramatically improved SNR over coils available for general use in the torso.

Adaptive antenna transmission for frequency duplex digital wireless communication

Abstract: Methods are reported for adaptive phased array transmission of digital wireless communication signals for the purpose of improving network call capacity. Frequency division duplex (FDD), time division multiple access (TDMA) communication channels are considered. The proposed techniques are designed for severe multipath environments with large Doppler, angle and delay spreads. No knowledge of array geometry, propagation path angles or portable feedback is required to adapt the transmission weight vectors. The time or frequency averaged spatial covariance of the received reverse link signal vector is decomposed into desired signal and interference subspaces which are used to form quadratic optimization problems involving matched filter bound cost functions. A dynamic channel allocation algorithm searches for frequency channels in which the adjacent cell portables are spatially compatible with the desired portable. Results of cellular network simulations are provided to illustrate the network call capacity improvements that are possible with the proposed FDD transmission approach.

Phased array radio frequency (RF) built-in-test equipment (BITE) apparatus and method of operation therefor

Abstract: Failure detection in a phased array antenna system is accomplished using a cluster-oriented detection scheme and a mutual coupling test signal injection technique. RF BITE TRM (110) is connected to an RF BITE port (120) on an illuminating means (140). Illuminating means (140) provides a uniform input signal level to many TRMs (150). Each TRM (150) is connected to an antenna element (210). Controller (170) causes one element (220) in a cluster to operate in a transmit mode and causes other elements (230) to operate in a receive mode. Internal detectors in TRMs (150) are used to detect signal levels, and these detected signal levels are used to identify failure modes. This cluster search method operates well for many types of phased arrays including rectangular and triangular lattices, planar and conformal apertures, single frequency and shared aperture types.

Integrated optical time delay unit

Abstract: A True Time Delay system for creating variable time delays of an optical signal suitable for use with a phased array antenna system in order to avoid beam-squint in broadband applications. The TTD is adapted to be integrated on a planar silica waveguide in order to substantially reduce the package size of the device. In one embodiment of the invention, the TTD is formed from a polarization beam splitter, a polarization rotator and a spiral waveguide. In an alternate embodiment of the invention, the TTD includes a polarization sensitive Mach Zehnder interferometer, a quarter wave polarization rotator and a spiral waveguide. In both embodiments of the invention Bragg reflective gratings are written into the spiral waveguide at different spacings to reflect optical signals of different wavelengths to create various time delays.

System-Level Integrated Circuit (SLIC) Technology Development for Phased Array Antenna Applications

Abstract: This report documents the efforts and progress in developing a 'system-level' integrated circuit, or SLIC, for application in advanced phased array antenna systems. The SLIC combines radio-frequency (RF) microelectronics, digital and analog support circuitry, and photonic interfaces into a single micro-hybrid assembly. Together, these technologies provide not only the amplitude and phase control necessary for electronic beam steering in the phased array, but also add thermally-compensated automatic gain control, health and status feedback, bias regulation, and reduced interconnect complexity. All circuitry is integrated into a compact, multilayer structure configured for use as a two-by-four element phased array module, operating at 20 Gigahertz, using a Microwave High-Density Interconnect (MHDI) process. The resultant hardware is constructed without conventional wirebonds, maintains tight inter-element spacing, and leads toward low-cost mass production. The measured performances and development issues associated with both the two-by-four element module and the constituent elements are presented. Additionally, a section of the report describes alternative architectures and applications supported by the SLIC electronics. Test results show excellent yield and performance of RF circuitry and full automatic gain control for multiple, independent channels. Digital control function, while suffering from lower manufacturing yield, also proved successful.

Manipulation of liquids using phased array generation of acoustic radiation pressure

Abstract: A phased array of piezoelectric transducers is used to control and manipulate contained as well as uncontained fluids in space and earth applications. The transducers in the phased array are individually activated while being commonly controlled to produce acoustic radiation pressure and acoustic streaming. The phased array is activated to produce a single pulse, a pulse burst or a continuous pulse to agitate, segregate or manipulate liquids and gases. The phased array generated acoustic radiation pressure is also useful in manipulating a drop, a bubble or other object immersed in a liquid. The transducers can be arranged in any number of layouts including linear single or multi-dimensional, space curved and annular arrays. The individual transducers in the array are activated by a controller, preferably driven by a computer.

Ultrabroadband, adaptive phased array antenna systems using microelectromechanical electromagnetic components

Abstract: A phased array radar system (50) employs programmable microelectromechanical (MEM) switches and transmission lines to provide true time delays or phase shifts in order to steer the array beam. The array includes an excitation signal source (70), a power division network (72) for dividing the excitation signal into a plurality of excitation signal components, a plurality of programmable time delay/phase shift circuits (100A-100E) including the transmission lines and MEM switches, and a plurality of radiating elements (60A-60E). An adaptive controller (80) provides the control signals to set the MEM switches and select the time delay\phase shift through each time delay/phase shift circuit, thereby steering the array beam to a desired direction.

Megalithic microwave signal processing for phased-array beamforming and steering

Abstract: A microwave signal processing (MSP) architecture is presented for active phased array beam forming and steering. A large scale network, comprising 63 power dividers and 32 pairs of vector-synthetic phase/amplitude controllers, has been successfully developed in an 11 mm/spl times/13 mm GaAs monolithic microwave integrated circuit (MMIC). It has a huge integration level of 128 metal-semiconductor field effect transmitters (MESFETs), 448 spiral inductors, 527 metal-insulator-metal (MIM) capacitors, and 357 ion-implanted resistors. The expected 360/spl deg/ phase is successfully obtained at all the output ports. Vector error standard deviations exhibited are within 0.38-dB root-mean square (rms) and 2.8/spl deg/ r.m.s. over the bandwidth of 20 MHz at 2.5 GHz. This megalithic chip could mark an epoch in phased array systems.

Contactless acoustic sensing system with detector array scanning and self-calibrating

Abstract: A contactless system for imaging an acoustic source within a workpiece directs a preferably annular optical probe beam pattern onto the vibrating workpiece surface, with the vibrationally modulated beam then detected by an array of preferably non-steady-state photo-emf detectors arranged in a similar pattern. The probe beam is scanned over the vibrating surface, either mechanically or through an electronically simulated phased array scheme. Time gating is used to suppress unwanted side-lobes when the individual detector outputs are summed over an appreciable waveband. A self-calibration scheme is also preferably used that provides a quantitative as well as qualitative output. A calibration modulation is imposed on at least one of the probe and reference beams, with the calibration modulation later removed at a post-detector stage and used to normalize the acoustic modulation output. Variations of the self-calibration scheme include reference-beam and time-delay interferometers based upon a calibrating phase modulation, and a photon flux measurement approach based upon a calibrating amplitude modulation.

Time-Steered Array with a Chirped Grating Beamformer

Abstract: Optical techniques for time-steered control of phased array antennas have been under intense study in recent years [1].

A method of reducing grating lobes associated with an ultrasound linear phased array intended for transrectal thermotherapy

Abstract: Some practical aspects of planar linear ultrasound phased arrays for transrectal thermotherapy of prostate diseases are discussed. Several regimens for driving the array are investigated and spatial distributions of ultrasound intensities are measured in water and compared with computer simulations. Practical recommendations for suppressing grating lobes based on the use of subsets of elements and de-activation of several elements in the array are given. Treatment safety could be increased by adopting these measures since the relative intensities and power in grating lobes and other secondary intensity peaks are decreased, as is the overall ultrasound energy introduced into the body without significant reduction in the maximum power at the focus.

A 2.5 MHz 2D array with Z-axis electrically conductive backing

Abstract: The design, fabrication and initial testing of a prototype fully /spl lambda//2 sampled, 2500 element 2D phased array is presented. The array utilizes a unique Z-axis electrical conductivity backing layer to provide both acoustic attenuation and electrical interconnect for the signal channels. The electrical interconnect is designed to be in the acoustic shadow of the transducer elements so as to minimize the foot print of the array. A modular, demountable Pad Grid Array interconnect is used to connect to the backing of the array. Results are presented for measurements of the single element properties of electrical impedance, pulse echo waveform and spectrum, directivity, and cross talk.

Method for determining orientation and attitude of a satellite- or aircraft-borne phased-array antenna

Abstract: A Tripulse method determines the orientation or attitude of a phased-array antenna located at a remote site, such as an aircraft or spacecraft. Three pulses are transmitted from the phased-array antenna in an estimated direction toward a coherent receiver, with a sum beam, and with first and second difference beams formed by reversal of the phase of certain elements above a first axis of symmetry, and to one side of a second axis of symmetry. The received signals are processed in a manner which determines the error between the assumed direction and the actual direction of the receiver. To determine the rotational position of the array antenna, the same steps are performed for a second remote receiver, and additional processing determines the complete attitude, including yaw, of the phased-array antenna. The coherent receiver may use the first transmitted pulse as a reference, or it may use a separate reference signal.

Two low-cost phased arrays

Abstract: In a phased array antenna, the phase shifters (or T/R modules in an active aperture phased array) with their beam-steering control circuitry along with the feed network account for the major hardware cost. This paper presents two antenna array configurations that use simpler feed, simpler phase-shifting and simpler beam-steering control circuitry for realizing low-cost phased arrays. Both are lens configurations. The first one uses a Radant lens, which provides a medium that is loaded with diodes and provides the needed phase shift by switching the diodes on and off. The other configuration employs a ferroelectric dielectric material whose dielectric constant can be varied with an applied DC bias voltage. It is shown that the ferroelectric lens may have further advantages of smaller thickness, simpler beam-steering controls and lower cost.

Superresolution for scanning antenna

Abstract: The MUSIC algorithm has been used widely in radar applications with spatially distributed sensor arrays. In those applications, the algorithm depends on the phase relations of the returned signal at different target pointing angles. Accordingly, many people believe that with a single narrow-beam antenna that is step-scanned in angle, the MUSIC algorithm cannot be used to superresolve target positions within the main beam, because there is no phase shift due to the scanning of the beam. This paper presents the application of the MUSIC algorithm to a scanning antenna that generates a nonuniform sensor vector. We call this application Scan MUSIC (SMUSIC). The simulation results with the SMUSIC algorithm for the spatial resolution of closely-spaced targets with a stepped-scan radar in the presence of Gaussian distributed noise are presented.

Effects of motion on adaptive arrays

Abstract: Adaptive beamforming procedures based on linear least-squares estimation of a wanted signal, such as the sample matrix inverse (SMI) algorithm, have been shown to successfully excise unwanted interference from the beamformer output. It is usually assumed that the signal environment is stationary, however under nonstationary conditions, such as those experienced by an array mounted on a rapidly moving platform, performance may be significantly degraded. The paper examines the effects of array motion on the structure of the sample covariance matrix and derives expressions for the resulting eigenvalues. These results are used to show that even when the same data is used both to compute the adaptive weights and to form the beamformer output, performance can be sensitive to extremely small movements of the array. In particular, simple closed-form expressions are derived for the limiting angular displacements of linear arrays which can be tolerated without significant performance degradation during the time taken to acquire sufficient data to update the weights.