Showing papers on "Phased array published in 1996"

Optical phased array technology

Abstract: Optical phased arrays represent an enabling new technology that makes possible simple affordable, lightweight, optical sensors offering very precise stabilization, random-access pointing programmable multiple simultaneous beams, a dynamic focus/defocus capability, and moderate to excellent optical power handling capability. These new arrays steer or otherwise operate on an already formed beam. A phase profile is imposed on an optical beam as it is either transmitted through or reflected from the phase shifter array. The imposed phase profile steers, focuses, fans out, or corrects phase aberrations on the beam. The array of optical phase shifters is realized through lithographic patterning of an electrical addressing network on the superstrate of a liquid crystal waveplate. Refractive index changes sufficiently large to realize full-wave differential phase shifts can be effected using low (<10 V) voltages applied to the liquid crystal phase plate electrodes. High efficiency large-angle steering with phased arrays requires phase shifter spacing on the order of a wavelength or less; consequently addressing issues make 1-D optical arrays much more practical than 2-D arrays. Orthogonal oriented 1-D phased arrays are used to deflect a beam in both dimensions. Optical phased arrays with apertures on the order of 4 cm by 4 cm have been fabricated for steering green, red, 1.06 /spl mu/m, and 10.6 /spl mu/m radiation. System concepts that include a passive acquisition sensor as well as a laser radar are presented.

Large angular dispersion by a virtually imaged phased array and its application to a wavelength demultiplexer.

Abstract: A new scheme that shows large angular dispersion is proposed and demonstrated. The key idea to this method is a virtually imaged phased array (VIPA). The angular dispersion of a VIPA is 10–20 times larger than those of common diffraction gratings, which have blaze angles of ~30 deg. With the VIPA, wavelength demultiplexing for 10 channels with 0.8-nm spacing is achieved. Low polarization-state dependence (~0.1 dB) is also confirmed.

Phased array ultrasound system and method for cardiac ablation

Abstract: An ultrasound system and method for performing relatively non-invasive cardiac ablation on a patient. The system of the present invention includes a plurality of ultrasound transducers forming a phased array that is to be located externally of the patient. The array a focused beam of sufficient energy to ablate a predetermined cardiac tissue volume. The system is capable of refocusing the beam so that acoustical aberrations encountered by the beam, as it is transmitted through inhomogeneous body tissues between the array and the treatment volume, are taken into account and will not impede operation of the system. To refocus the beam, the system includes a senor which senses the phase distribution caused by the aberrations allowing a controller to calculate a compensating driving phase distribution and accordingly drive the array. The system also allows for real time correction of the beam's position enabling the beam to follow a moving myocardial target volume.

Balanced antipodal Vivaldi antenna for wide bandwidth phased arrays

Abstract: The Vivaldi antenna, a form of tapered slot radiator, has been shown to produce good performance over a wide bandwidth, limited only by the traditionally used slotline to microstrip feed transition. The authors present a new antenna, the balanced antipodal Vivaldi, which incorporates an ultrawide bandwidth transition and overcomes the poor polarisation performance of the antipodal form. Good performance over a 1 to 40 frequency range has been obtained. The use of the antenna in a linear phased array has also been investigated using elements constructed on high permittivity substrate. Wideband wide angle scanning with good cross-polarisation levels is obtained.

High-efficiency liquid-crystal optical phased-array beam steering

Abstract: Efficient, electrically tunable, agile, inertialess, near-diffraction-limited one-dimensional optical beam steering is demonstrated at the infrared wavelength of 10.6 microm with a liquid-crystal phased array.

Optimizing the radiation pattern of sparse periodic linear arrays

Abstract: We have developed a method for designing sparse periodic arrays. Grating lobes in the two-way radiation pattern are avoided by using different element spacings on transmission and reception. The transmit and receive aperture functions are selected such that the convolution of the aperture functions produces a desired effective aperture. A desired effective aperture is simply an aperture with an appropriate width, element spacing, and shape such that the Fourier transform of this function gives the desired two-way radiation pattern. If a synthetic aperture approach is used, an exact solution to the problem is possible. However, for conventional imaging, often only an approximation of the desired effective aperture can be found. Different strategies for obtaining these approximate solutions are described. The radiation pattern of a sparse array designed using the effective aperture concept is compared experimentally with the radiation patterns of a dense array, and sparse arrays with periodic and random element spacing. We show that the number of elements in a 128-element linear array can be reduced by at least four times with little degradation of the beam forming properties of the array.

Phased array antenna with temperature compensating capability

Abstract: Generally, a variation of temperature at the installation site causes a phased array antenna radiation pattern to degrade. This paper describes the temperature characteristics of various components of the phased array antenna and degradations of the radiation pattern originating from temperature variations. It is effective to measure the phase distribution on the aperture and correct it, as the occasion demands, to prevent such degradations. Also, we propose a simple and effective algorithm for the measurement of the current distribution on the aperture, and present the evaluation test results of a phased array antenna with temperature compensation obtained by applying the algorithm.

Noninvasive real-time multipoint temperature control for ultrasound phased array treatments

Abstract: A method for noninvasively estimating spatiotemporal temperature changes in samples using diagnostic ultrasound, and using these as inputs to a multipoint ultrasound phased array temperature controller, is presented in this paper. This method is based on a linear relationship between the apparent tissue echo pattern displacements and temperature, as seen along A-lines acquired with diagnostic ultrasound when the sample is heated by external heating fields. The proportionality constant between echo displacement and temperature is determined by the local change in speed of sound due to temperature and the linear coefficient of thermal expansion of the material. Accurate estimation of the displacements and proportionality constant yields accurate calibrated high-resolution (1 mm spatial, sub-/spl deg/C) noninvasive sample temperature estimates. These are used as inputs to a multipoint temperature controller, capable of controlling ultrasound phased array treatments in real-time. Phantom and in vitro results show that the noninvasively estimated temperature values can effectively be used to control ultrasound hyperthermia treatments, almost replacing invasive thermocouple measurements. The mathematical background and assumptions of the noninvasive temperature estimator and the controller are presented in this paper, together with experimental results showing estimator and controller performance and limitations. To the best of our knowledge, this paper presents the first demonstration of real-time treatment control based entirely on noninvasive temperature estimates.

Method and apparatus for adaptive transmission beam forming in a wireless communication system

Abstract: A method for forming an adaptive phased array transmission beam pattern at a base station without any knowledge of array geometry or mobile feedback is described. The approach is immune to the problems which plague methods which attempt to identify received angles of arrival from the mobile and map this information to an optimum transmit beam pattern. In addition, this approach does not suffer the capacity penalty and mobile handset complexity increase associated with mobile feedback. Estimates of the receive vector propagation channels are used to estimate transmit vector channel covariance matrices which form objectives and constraints in quadratic optimization problems leading to optimum beam former solutions for the single user case, and multiple user case. The new invention in capable of substantial frequency re-use capacity improvement in a multiple user cellular network.

Simulation studies promote technological development of radiofrequency phased array hyperthermia.

Abstract: A treatment planning program package for radiofrequency hyperthermia has been developed. It consists of software modules for processing three-dimensional computerized tomography (CT) data sets, manual segmentation, generation of tetrahedral grids, numerical calculation and optimisation of three-dimensional E field distributions using a volume surface integral equation algorithm as well as temperature distributions using an adaptive multilevel finite-elements code, and graphical tools for simultaneous representation of CT data and simulation results. Heat treatments are limited by hot spots in healthy tissues caused by E field maxima at electrical interfaces (bone/muscle). In order to reduce or avoid hot spots suitable objective functions are derived from power deposition patterns and temperature distributions, and are utilised to optimise antenna parameters (phases, amplitudes). The simulation and optimisation tools have been applied to estimate the improvements that could be reached by upgrades of the clinically used SIGMA-60 applicator (consisting of a single ring of four antenna pairs). The investigated upgrades are increased number of antennas and channels (triple-ring of 3 x 8 antennas and variation of antenna inclination. Significant improvement of index temperatures (1-2 degrees C) is achieved by upgrading the single ring to a triple ring with free phase selection for every antenna or antenna pair. Antenna amplitudes and inclinations proved as less important parameters.

Experimental demonstration of a phased-array antenna optically controlled with phase and time delays

Abstract: The experimental demonstration and the far-field pattern characterization of an optically controlled phased-array antenna are described. It operates between 2.5 and 3.5 GHz and is made of 16 radiating elements. The optical control uses a two-dimensional architecture based on free-space propagation and on polarization switching by N spatial light modulators of p × p pixels. It provides 2N−1 time-delay values and an analog control of the 0 to 2π phase for each of the p × p signals feeding the antenna (N = 5, p = 4).

Sparse random ultrasound phased array for focal surgery

Abstract: Ultrasound phased arrays offer several advantages over single focused transducer technology, enabling electronically programmable synthesis of focal size and shape, as well as position. While phased arrays have been employed for medical diagnostic and therapeutic (hyperthermia) applications, there remain fundamental problems associated with their use for surgery. These problems stem largely from the small size of each array element dictated by the wavelength employed at surgical application frequencies (2-4 MHz), the array aperture size required for the desired focal characteristics, and the number of array elements and electronic drive channels required to provide RF energy to the entire array. The present work involves the theoretical and experimental examination of novel ultrasound phased arrays consisting of array elements larger than one wavelength, minimizing the number of elements in an aperture through a combination of geometric focusing, directive beams, and sparse random placement of array elements, for tissue ablation applications. A hexagonally packed array consisting of 108 8-mm-diameter circular elements mounted on a spherical shell was modeled theoretically and a prototype array was constructed to examine the feasibility of sparse random array configurations for focal surgery. A randomly selected subset of elements of the prototype test array (64 of 108 available channels) was driven at 2.1 MHz with a 64-channel digitally controlled RF drive system. The performance of the prototype array was evaluated by comparing field data obtained from theoretical modeling to that obtained experimentally via hydrophone scanning. The results of that comparison, along with total acoustic power measurements, suggest that the use of sparse random phased arrays for focal surgery is feasible, and that the nature of array packing is an important determinant to observed performance.

Multiband phased-array antenna with interleaved tapered-elements and waveguide radiators

Abstract: Multiband, multibeam, phased array antennas are required for today's multi-function radar and communication applications. These types of antennas play a major role in the shipboard and airborne environment, where space is limited. A single antenna is now asked to perform multiple functions, including long-range surveillance, navigation, weapons control, tracking and recognition, and electronic warfare support measures. A phased array antenna capable of covering several different frequency bands in a common aperture is highly desirable, and is currently being pursued for many of these applications. A number of multiband radar antenna configurations have been proposed in the past. An ultra-wideband phased array antenna design using interleaved waveguide elements and wideband tapered elements is presented. This phased array antenna can operate over at least three frequency bands. Numerical results of the aperture match for both types of radiators, including mutual interaction, are presented.

Intensity correction of phased‐array surface coil images

Abstract: Phased-array coils distribute the high signal-to-noise ratio (SNR) performance of their small component surface coils over the larger area covered by the entire array. The inhomogeneous sensitivity profiles of the component surface coils result in images with very high signal near the phased-array and decreased signal far from the array. This paper presents a postprocessing algorithm for correcting these coil-related intensity variations. The algorithm's performance was evaluated by correcting images of volunteers acquired with several different receive-only phased-array surface coils.

Phased array beam controller using integrated electro-optic circuits

Abstract: A photonic device for controlling phased array beam direction includes an electro-optic substrate; a plurality of waveguides formed in the substrate, each of which is capable of simultaneously propagating light signals with orthogonal polarizations; an input waveguide for inputting into each one of the plurality of waveguides a pair of copropagating polarized light signals having orthogonal polarizations and different frequencies; a plurality of electrodes on the substrate configured to phase shift the signals traveling through each waveguide by a different amount in response to a common applied voltage, thereby creating phase shifted polarized signals; and means for combining the phase shifted polarized signals within each one of the waveguides and propagating these combined signal to an antenna element The basic operating principle of the invention is based on the differential phase shift between optical waves of orthogonal polarizations traveling in an electro-optic optical waveguide This differential phase shift is directly proportional to the voltage applied to a control electrode and to the length of that electrode If the two optical waves are slightly offset in optical frequency, they produce a beat frequency when photodetected whose phase shift equals the optical differential phase shift An array of such phase shifters forms the basis for the photonic beam controller of the invention

Low-cost communication phased-array antenna

Abstract: A phased-array antenna structure is provided that includes an antenna waveguide structure (404) with a plurality of waveguides (406). The antenna waveguide structure propagates the received or transmitted electromagnetic (EM) signals within the plurality of waveguides to a corresponding active array module (408). Each active array module amplifies and adjusts the phase of a received or transmitted EM signal. The active array modules are coupled to an interconnect structure (416) that provides EM signal propagation paths, as well as power and digital signal paths, to and from the active array modules. A plate (420) is coupled to the interconnect structure and the antenna waveguide structure to support the antenna waveguide structure, the electronic modules, and the interconnect structure, thereby forming a rigid unit and keeping the electronic modules in alignment with their corresponding waveguides in the antenna waveguide structure. The plate also includes waveguides for propagating the EM signals from the interconnect structure to the antenna output. The active array modules each include an integrated polarizer for selectably operating with either right-hand circularly polarized signals or left-hand polarized signals. The polarizer, amplifiers and phase shifters are mounted on a substrate in each active array module, with the substrate disposed in a position normal to the propagation of the EM signals in the corresponding waveguide of the antenna waveguide structure, resulting in a planar configuration. Further, each active array module includes a waveguide as an integral part of the active array module.

Feasibility of using ultrasound phased arrays for MRI monitored noninvasive surgery

Abstract: The purpose of this paper was to evaluate the in vivo feasibility of using phased arrays for MRI guided ultrasound surgery. Two different array concepts were investigated: a spherically curved concentric ring array to move the focus along the central axis and a spherically curved 16 square element array to make the focus larger. Rabbit thigh muscles were exposed in vivo in a 1.5 T MRI scanner to evaluate the array performance. The results showed that both of the arrays performed as expected, and the focus could be moved and enlarged. In addition, adequate power could be delivered from the arrays to necrose in vivo muscle tissue in 10 s. This study was the first implementation of phased arrays for MRI guided ultrasound surgery. The results demonstrate that phased arrays have significant potential for noninvasive tissue coagulation.

A novel multiwavelength optically controlled phased array antenna with a programmable dispersion matrix

Abstract: We propose and demonstrate a "programmable-dispersion" matrix (PDM) for a novel multiwavelength optically controlled phased array antenna (MWOCPAA). The PDM, when employed in conjunction with a multiwavelength source, generates all the time delays for the entire array. In this multiwavelength control scheme, an optical wavelength-to-array element correspondence is established and there is no splitting loss associated with signal distribution to array elements. The time delays are controlled by the dispersion of the PDM which can be programmed by optical switches. Experimental results demonstrating the feasibility of the MWOCPAA are presented. Broadband linear RF phase shift is measured among various wavelength channels.

Voltage controlled ferroelectric lens phased arrays

Abstract: Phased array antennas can steer transmitted and received signals without mechanically rotating the antenna. Each radiating element of a phased array is normally connected to a phase shifter, which determines the phase of the signal at each element to form a beam at the desired angle. The most commonly used phase shifters are ferrite and diode phase shifters. Phase shifters using ferroelectric materials have been proposed previously. A typical phased array may have several thousand elements and is very expensive. Therefore, reducing the cost and complexity of the phase shifters and the phase shifter controls is an important consideration in the design of phased arrays. The phased array described uniquely incorporates bulk phase shifting, the array does not contain individual phase shifting, using a ferroelectric material along with simpler phase shift control. Bulk phase shifting using diodes has been proposed and developed in the Radant lens. The lens described uses a voltage controlled ferroelectric, which introduces an analog phase shift rather than a digital phase shift as in the Radant lens. The ferroelectric lens has further advantages of smaller lens thickness, higher power handling, simpler beam steering controls, and it uses less power to control the phase shift compared to the Radant lens. Thus, it can potentially lead to low cost phased arrays.

Design and optimization of an aperiodic ultrasound phased array for intracavitary prostate thermal therapies

Abstract: A 57 element aperiodic linear phased array was designed and constructed to investigate the feasibility of using transrectal ultrasound for the thermal therapeutic treatment of prostate cancer and benign prostatic hyperplasia. A method of reducing grating lobe levels by using optimized random distributions of unequally sized elements is introduced. Using this technique, array periodicity is avoided, making it feasible to use larger elements and hence fewer elements and amplifier channels, while still achieving acceptable power field patterns. Acoustic power field simulations determined that the grating lobe levels associated with selected aperiodic element distributions were approximately 30%–45% less than those associated with periodic element spacing and the same average element width. Or by using aperiodic rather than periodic element distributions, the average element width could be increased by approximately 20%–35% (∼λ/4.4), while maintaining a constant grating lobe level. Prior to construction of the 57 element array, the power capabilities of this type of array were demonstrated with a 16 element aperiodic phased array, which delivered over 28 W of acoustical power per cm of array length while focused. The power field patterns produced by the 57 element array closely matched the field patterns predicted by the theoretical model used in the simulations. The array produced acceptable power field patterns for foci at depths up to 5 cm and up to 2 cm off the center axis, in addition to producing multiple foci simultaneously. Based on the power capabilities and field patterns, this aperiodic array design has the potential to be incorporated into a clinical heating device as a means of delivering thermal therapies to the prostate and other target volumes close to body cavities.

Smart aperture antennas

Abstract: Recent studies have shown that reflector surface adaptation can achieve performance characteristics of the order of phase array antennas without their complexity and cost. This study develops a class of antennas capable of variable directivity (beam steering) and power density (beam shaping). The actuation for these antennas is employed by attaching polyvinylidene fluoride (PVDF) film to a metallized Mylar substrate. A voltage drop across the material will cause the material to expand or contract. This movement causes a moment to be developed in the structure which causes the structure to change shape. Several studies of flexible structures with PVDF films have shown that cylindrical antennas can achieve significant deflections and thereby offer beneficial changes to radiation patterns emanating from aperture antennas. In this study, relatively large curved actuators are modelled and a deflection - force relationship is developed. This relationship is then employed in simulations where the far-field radiation patterns of an aperture antenna are manipulated.

Recirculating photonic filter: a wavelength-selective time delay for phased-array antennas and wavelength code-division multiple access.

Abstract: A novel wavelength-selective photonic time-delay filter is proposed and demonstrated. The device consists of an optical phased-array waveguide grating in a recirculating feedback configuration. It can function as a true-time-delay generator for squint-free beam steering in optically controlled phased-array antennas and as an encoding–decoding filter for wavelength code-division multiple access.

VLSI systolic arrays for adaptive nulling [radar]

Abstract: Presents a case study of the design of a computationally intensive system to do adaptive nulling of interfering signals for a phased-array radar with many antenna elements. The goal of the design was to increase the computational horsepower available for this problem by about three orders of magnitude under the tight constraints of size, weight and power which are typical of an orbiting satellite. By combining the CORDIC rotation algorithm, systolic array concepts, Givens transformations, and restructurable VLSI, we built a system as small as a package of cigarettes, but capable of the equivalent of almost three billion operations per second. Our work was motivated by the severe limitations of size, weight and power which apply to computation aboard a spacecraft, although the same factors impose costs which are worth reducing in other circumstances. For an array of N antennas, the cost of the adaptive nulling computation grows as N/sup 3/, so simply using more resources when N is large is not practical. The architecture developed, called MUSE (matrix update systolic experiment) determines the nulling weights for N=64 antenna elements in a sidelobe cancelling configuration. After explaining the antenna nulling system, we discuss another DSP computation that might benefit from similar architecture, technology, or algorithms: the solution of Toeplitz linear equations.

Intracavitary ultrasound phased arrays for noninvasive prostate surgery

Abstract: The feasibility of using intracavitary ultrasound phased arrays for thermal surgery of the prostate was investigated. A simulation study was performed which demonstrated the ability of phased arrays to generate necrosed tissue volumes over anatomically appropriate ranges (2-6 cm deep and >6 cm axially) and investigated the effects of varying frequency, sonication time, maximum temperature, and blood perfusion on the necrosed tissue volume. An advantage that phased arrays have over geometrically focused transducers is that they are able to electronically scan a single focus over a specified range very quickly. This study demonstrated that the necrosed tissue volume may be increased by more than a factor of 100 by using electronic scanning. Scan parameters that were investigated included foci spacing, scan width, perfusion, maximum temperature, and unequal weighting of the foci. An optimization was performed to select the foci weighting parameters such that a uniform thermal dose was achieved at the focal depth, providing a more uniformly heated target volume. Finally, the ability of linear ultrasound phased arrays to create necrosed tissue lesions was demonstrated experimentally in fresh beef liver using a single stationary focus and single focus scans generated by an aperiodic 0.83-MHz 57-element linear ultrasound phased array.

An efficient scheduling algorithm for a multifunction radar

Abstract: The new generation of air defence frigates has to be equipped with a high performance sensor suite to cope with the threat in future maritime scenarios. A multifunction radar (MFR) with a single rotating or multiple fixed phased array antennas is often the key element in this sensor suite because it can perform not only surveillance functions but also missile support. Since the MFR must be able to execute multiple functions concurrently, a scheduling mechanism is required that allocates the time and energy resources of the MFR to the radar functions in such a way that the overall performance of the sensor suite is optimized. This paper describes an efficient scheduling algorithm that is able to schedule the dwell requests of each function on the basis of their priority and transmission window. Some results are shown of the scheduling algorithm in a typical scenario in which a number of seaskimmers is engaged by semi-active surface-to-air missiles.

A study of various parameters of spherically curved phased arrays for noninvasive ultrasound surgery

Abstract: The spherically curved square element phased array design for ultrasound surgery was studied in several of its important aspects. A method for determining the spatial limitations of the multiple-foci region was developed for spherically curved phased arrays. The effects on the ultrasound fields of varying the phases and the amplitudes at control points were investigated. It was found that the phases and the magnitudes of control points have an impact on the ultrasound field distributions. The effects of multiple-foci spacing, pulse duration, and maximum temperature on the size and shape of necrosed tissue were investigated. For a spherically curved phased array with an 8 cm radius of curvature, an 8.8 x 8.8 cm2 projected area, and a 1.5 MHz operating frequency, the minimum number of phased array elements that could produce the largest acceptable necrosed tissue volume was 256. The tissue volume necrosed during the sonication could be increased to approximately 1 x 1 x 3 cm3 with this array.

Polymeric phased array wavelength multiplexer operating around 1550 nm

Abstract: A polymeric, optical fibre compatible, 8/spl times/8 phased array wavelength multiplexer with 400 GHz (3.2 nm) channel spacing, has been designed and realised for operation in the 1550 nm erbium doped fibre amplifier (EDFA) window. By using bending radii as small as 20 mm, the device measures only 64/spl times/4 mm. The fibre to fibre insertion loss in the passbands varies between 6.6 and 8.0 dB and the crosstalk is -25 dB.

An in-space wireless energy transmission experiment

Abstract: The concept for an orbiting power satellite capable of supplying the needs of several co-orbiting manufacturing satellites is similar to the central power station and distribution network found on Earth. An experiment for testing a portion of such an "Orbital Power and Light" space power utility system-a retrodirective phased array energy transmission system in space-is described. The experiment will demonstrate the ability of a wireless power transmission system to acquire and maintain a target in space. The experiment will consist of a planar phased array antenna on the Space Shuttle beaming to a target rectenna with a pilot guide beam on the free flying Wake Shield Facility (WSF).