Showing papers on "Phased array published in 1995"

Synthetic aperture imaging for small scale systems

Abstract: Multi-element synthetic aperture imaging methods suitable for applications with severe cost and size limitations are explored. Array apertures are synthesized using an active multi-element receive subaperture and a multi-element transmit subaperture defocused to emulate a single-element spatial response with high acoustic power. Echo signals are recorded independently by individual elements of the receive subaperture. Each method uses different spatial frequencies and acquisition strategies for imaging, and therefore different sets of active transmit/receive element combinations. Following acquisition, image points are reconstructed using the complete data set with full dynamic focus on both transmit and receive. Various factors affecting image quality have been evaluated and compared to conventional imagers through measurements with a 3.5 MHz, 128-element transducer array on different gel phantoms. Multielement synthetic aperture methods achieve higher electronic signal to noise ratio and better contrast resolution than conventional synthetic aperture techniques, approaching conventional phased array performance. >

Optically generated true-time delay in phased-array antennas

Abstract: This tutorial review paper deals with various methods for solving a basic problem of wideband phased arrays, i.e. beam squinting, using optical technologies. The problem of beam squinting in phased arrays is analyzed and the concept of true-time delay is introduced. The advantages of realizing variable delay lines by optical rather than by microwave means are reviewed, together with principles of operation. Among the techniques described are switched-path length delay lines, fiber stretchers, tunable lasers with highly dispersive fiber, and coherent techniques incorporating dispersive delay. Recent experimental results are discussed in the light of practical system requirements. >

The SIR-C/X-SAR Synthetic Aperture Radar system

Abstract: The Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) was a joint United States/German/Italian space agency imaging radar system successfully flown aboard the shuttle Endeavor in April 1994 and again in September/October 1994. The multifaceted SIR-C/X-SAR represents a major technological step forward in radar remote sensing and is the first spaceborne multifrequency, polarimetric SAR. The United States developed SIR-C operated at L- and C-band, each with quad polarization. The SIR-C antenna was an active phased array, with the capability for electronic beam steering and multiple swath width illumination. The German/Italian X-SAR operated at X-band with a single polarization using a slotted waveguide antenna, mechanically steerable in elevation. SIR-C and X-SAR were designed to operate synchronously, collecting data over common sites synchronously. A total of 143 hours (93 terabits) of SAR data were recorded on tape. >

Polarization diversity phased array cellular base station and associated methods

Abstract: A base station includes first and second antenna arrays for receiving first and second rotational polarizations, and a polarization diversity receiver connected to the first and second antenna arrays for processing respective first and second receive signals from a mobile station to generate an enhanced quality output receive signal based upon polarization diversity reception. Polarization isolation between the transmit and receive antenna elements may also provided by having a first plurality of transmit antenna elements for the second polarization mounted on a substrate carrying the first receive antenna elements. The second antenna array includes a second plurality of antenna elements of second polarization on a substrate carrying the second receive antenna elements. To achieve polarization diversity gain at the mobile station, the base station preferably further includes an alternating polarization transmitter for alternately transmitting signals at respective alternating first and second rotational polarizations. Method aspects of the invention are also disclosed.

A blind adaptive transmit antenna algorithm for wireless communication

Abstract: A method is proposed for forming an adaptive phased array transmission beam pattern at a base station without any knowledge of array geometry, path angles or mobile feedback. Estimates of receive vector channels are used to form a transmit weight vector optimization problem. The authors provide closed form solutions for both the single user case and the multiple user case. They show through simulation of a multiple user cellular network that the cooperative transmission network algorithm is capable of improving network frequency re-use capacity by a factor of 5 to 8.

Analog reflection topology building blocks for adaptive microwave signal processing applications

Abstract: The synthesis and realization of an analog-phase shifter, delay line, attenuator, and group delay synthesizer-are presented. These variable control devices are all implemented using the same generic single stage reflection topology. The optimum conditions of operation have been determined and the corresponding group delay behaviors have been investigated to produce simple design equations. As proof-of-concepts, monolithic technology has been used to realize an X-band, phase shifter, delay line, and attenuator. Hybrid technology has been used to realize an L-band, group-delay synthesizer. Because of the high levels of performance measured, these control devices are ideally suited for use as general building blocks in adaptive signal processing applications, including large phased array applications. >

Phased array detectors and an automated intensity-correction algorithm for high-resolution MR imaging of the human brain.

Abstract: Two- and four-coil phased array detectors were developed to increase the sensitivity and resolution of MR imaging of the human brain cortex, especially for detecting cortical dysplasias in pediatric epilepsy patients. An automated intensity correction algorithm based on an edge-completed, low-pass filtered image was used to correct the image intensity for the inhomogenous reception profile of the coils. Seven phased array coils were constructed and tested. The sensitivity of these coils was up to 600% higher at the surface of the cortex than that achieved with a conventional head coil and up to 30% greater at the center of the head. The sensitivity obtained was comparable with that of a conventional small surface coil, but extended over the larger dimensions of the array and previously inaccessible areas such as the top of the head. The advantages of the improved sensitivity are demonstrated with high resolution images of the brain.

Adaptive beam forming for transmitter operation 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.

Direction finding and "smart antennas" using software radio architectures

Abstract: Operational tests and demonstrations of systems based on software radios are currently being performed in the 800 MHz mobile cellular radio band. These field trials are for mobile unit geolocation systems and adaptive phased array "smart antenna" applications. The geolocation system trials are in response to the demand for high confidence geolocation of mobile units for enhanced emergency 911 service and for use in the US Department of Transportation's Intelligent Vehicle Highway System (NHS) initiative. The smart antenna array application addresses the cellular service providers' need for more user channel capacity and/or geographic coverage from existing base station installations. Software radio architectures were selected because of their ability to provide superior performance at low life cycle cost. These systems use 4 to 8 wideband coherent channels and fully characterize the arriving RF energy to either geolocate the emitter or to maximize the carrier-to-interference ratio. >

Phased array antenna management system and calibration method

Abstract: A management system and calibration method for use with a phased array antenna that increases its robustness to component changes or failures. The present invention employs a system level measurement of amplitude and phase, conducted during nodal operation, to determine on an element by element basis, the tracking performance of individual chains that for the antennas. This amplitude and phase information is employed to compensate the each chain for the measured error. The present system and method measures the amplitude and phase of individual element chains utilizing probe carriers. The required correction coefficients for each chain is determined from the measured amplitude and phase data, and each individual element chain is individually compensated to remedy the amplitude and phase errors. The present system and method generates a probe carrier that is applied to each element chain along with normal communication signal waveforms. The probe carrier is sufficiently small (narrow bandwidth, low power, or encoded) so that it does not significantly degrade system operation. The relative amplitude and phase of the probe carrier, as applied to an element chain, is measured. By switching the probe carrier in time sequence between each chain, the differential amplitude and phase characteristics of each of the chains is determined. This also serves to detect component failures in a chain. Each chain includes commandable amplitude and phase weighting networks. Once the differential amplitude and phase tracing characteristics of the antenna re characterized, the individual weighting networks are commanded to settings that compensate for the measured values.

Photonic wideband array antennas

Abstract: Presents an introduction to the optical control of array antennas by using fiber optic links for remote control and a photonic time shift network for wide instantaneous bandwidth. An overview of the development of a wideband conformal array designed for airborne surveillance radars is given. The paper covers the system design and the performance of an L-band (850-1400 MHz) M-element array controlled by photonics. Packaging techniques of the photonic components and the array aperture are discussed. The wideband performance of the system is highlighted. A nano-second impulse response has been measured to demonstrate a 50% instantaneous bandwidth (550 MHz, 30 cm range resolution) for target ID and imaging. A built-in signal injection technique based on time-domain impulse measurement was used to calibrate the wideband components in the time-shift beamforming network. >

Phased array cellular base station and associated methods for enhanced power efficiency

Abstract: A base station includes a radio channel generating circuit for generating a plurality of individual radio channel signals each at a different frequency from one another, and a plurality of individual phased array antennas operatively connected to the radio channel generating circuit so that each individual phased array antenna transmits only one individual radio channel signal at a time. Each of the phased array antennas preferably includes a substrate and a plurality of radiating elements mounted thereon in a predetermined pattern. Each radiating element is readily provided by a stripline, and the substrate is preferably a circuit board. Accordingly, another feature of the base station according to the invention is that power radiated by each phased array antenna can be selectively controlled to reduce possible interference while maintaining communications with respective mobile units that are both near and far from the base station. A switch may be provided between the radio channel generating circuit and the phased array antennas to facilitate cell splitting. Method aspects for operating the base station are also disclosed.

High performance circularly polarized microstrip antenna

Abstract: A microstrip antenna for radiating circularly polarized electromagnetic waves comprising a cluster array (20) of at least four microstrip radiator elements (22a-22d), each of which is provided with dual orthogonal coplanar feeds in phase quadrature relation achieved by connection to an asymmetric T-junction power divider (30) impedance notched at resonance. The dual fed circularly polarized reference element is positioned with its axis at a 45° angle with respect to the unit cell axis. The other three dual fed elements in the unit cell are positioned and fed with a coplanar feed structure with sequential rotation and phasing to enhance the axial ratio and impedance matching performance over a wide bandwidth. The centers of the radiator elements are disposed at the corners of a square with each side of a length d in the range of 0.7 to 0.9 times the free space wavelength of the antenna radiation and the radiator elements reside in a square unit cell area of sides equal to 2d and thereby permit the array to be used as a phased array antenna for electronic scanning and is realizable in a high temperature superconducting thin film material for high efficiency.

SIR-C data quality and calibration results

Abstract: The SIR-C/X-SAR imaging radar took its first flight on the Space Shuttle Endeavour in April 1994 and flew for a second time in October 1994. This multifrequency radar has fully polarimetric capability at L- and C-band, and a single polarization at X-band (X-SAR). The Endeavour missions were designated the Space Radar Laboratory-1 (SRL-1) and -2 (SRL-2). Calibration of polarimetric L- and C-band data for all the different modes SIR-C offers is an especially complicated problem. The solution involves extensive analysis of pre-flight test data to come up with a model of the system, analysis of in-flight test data to determine the antenna pattern and gains of the system during operation, and analysis of data from over fourteen calibration sites distributed around the SIR-C/X-SAR orbit track. The SRL missions were the first time a multifrequency polarimetric imaging radar employing a phased array antenna has been flown in space. Calibration of SIR-C data products involved some unique technical problems given the complexity of the radar system. In this paper, the approach adopted for calibration of SIR-C data is described and the calibration performance of the data products is presented. >

SAR optimization in a phased array radiofrequency hyperthermia system

Abstract: RF deep hyperthermia systems make use of phased arrays of applicators in order to heat tumors selectively while maintaining healthy tissue at normal temperatures. A new method for the array synthesis is proposed based on the identification of targets to be heated (tumors) and targets to be prevented from excess electromagnetic radiation. The best array feed for each target is found from the solution of the eigenvector problem for a positive definite Hermitian matrix defined for that target. The optimal feed in a global sense then results from a trade-off of the best feeds of individual targets enforced through minimization of an objective function aimed at weighting the distances of the globally optimal feed from the feed vectors optimized for each target separately. An application to the heating of a pelvis is provided as an example.

Active noise control system using phased-array sensors

Abstract: An active noise control system is provided with a plurality of error sensor arrays (50, 77) which provide signals on lines (64-74, 90-100) to beam forming and beam steering logic (76) which cause the arrays (50, 77) to exhibit acoustic response profiles (104, 106), respectively. The profiles (104, 106) intersect in a predefined region (116) to be quieted. The logic (76) provides signals on lines (118), one for each region to be quieted, to active noise control (ANC) logic (20) which also receives inputs from feedforward sensing microphones (10) and provides output signals to acoustic speakers (24) which generate anti-noise (26) to cancel the noise in the quiet region (116). The quiet region (116) may be selectively positioned to any region in the room by steering the beams (104, 108). Alternatively, the system may have a plurality of distributed sensors which, when taken together, have an overall maximum (main lobe) acoustic response at a predetermined selectable quiet region.

Multiple beamwidth phased array

Abstract: A system for wireless communication between at least one first station and a plurality of second stations using a relay station is disclosed. The relay station contains, among other features, an antenna array and a multi-channel transponder. The antenna array has a plurality of antenna elements which are divided into two sets. The first set is used to provide transmission or reception using beams having a first beamwidth and the second set is used to provide transmission or reception using beams having a second beamwidth. The multi-channel transponder, which is connected to the antenna array and a feeder link antenna, receives feeder link signals from at least one of the first stations and converts the signals into drive signals for the antenna array elements. The multi-channel transponder has a first channel bandwidth for channels transponding signals for transmissions having the first beamwidth and a second channel bandwidth for channels transponding signals for transmissions having said second beamwith. The plurality of second stations is divided dynamically by a switching system into at least a first group that use the narrowest beamwidth and a second group that use the widest beamwidth, according to the path loss requirements for each group.

Phased array spread spectrum system and method

Abstract: A phased array spread-spectrum system maximizes signal strength of a spread-spectrum signal with multipath. RF/IF section (21) receives a plurality of spread-spectrum signals. RF/IF section (22) receives a plurality of phased versions of the plurality of spread-spectrum signals. Digital delay devices (27, 28) delay the received spread-spectrum signals with respect to their phased versions by a plurality of delays. Summers (29, 30) combine the delayed spread-spectrum signals and their phased versions as a plurality of combined signals. Despreader (31) despreads the combined signals as a plurality of despread signals. Magnitude device (32) generates a plurality of magnitude values from the despread signals. Shift register (33) stores a plurality of previous-magnitude values and present-magnitude values previously and presently generated by the magnitude device (32). Comparator (34) compares the previous-magnitude values to the present-magnitude values and outputs a plurality of comparison signals. Digital delay devices (27, 28), responsive to the comparison signals, lengthen or shorten the plurality of delays.

Fibre grating time delay element for phased array antennas

Abstract: The authors have demonstrated an optical fibre grating based delay line which produces time delays in increments as small as 31 ps. The device could provide a true time delay component for a phased array antenna

Proton spectroscopic imaging of the human brain using phased array detectors.

Abstract: Two and four-coil phased array detectors have been developed to increase the sensitivity of proton spectroscopic imaging of the human brain. These include a quadrature figure-8 coil for the study of the vertex, several arrays of 2-4 small overlapping (6-8 cm diameter) circular coils and a combination figure-8 coil plus circular coil. These were constructed in our laboratory and tested to assess their utility for brain spectroscopy. Methods for optimally combining the data from the independent receivers based on the analytical coil maps or measured signal to noise ratios (SNRs) of the data were investigated. High spatial resolution (0.2-0.4 cm3 voxel size) two- or three-dimensional chemical shift images of normal brain were obtained in 17-minute acquisitions. These spatial resolutions are comparable to those previously obtained with conventional small surface coils, but the specialized detectors allow this sensitivity to be achieved for a larger region or for previously inaccessible areas such as the top of the head. The coverage and SNR increases demonstrated are similar to those obtained in magnetic resonance phased array imaging.

Time multiplexed digital ultrasound beamformer

Abstract: A phased array digital ultrasound beamformer for use with an ultrasound transducer array. The beamformer includes a processing channel for each element of the transducer array. Each processing channel includes a digitizing circuit for converting the received signal to digital samples and a time multiplexed digital delay circuit responsive to delay coefficients for delaying the digital samples by time multiplexed delays to produce delayed, time multiplexed samples for forming two or more receive beams. The ultrasound beamformer further includes a summing circuit for summing the delayed, time multiplexed digital samples from each processing channel to form a stream of time multiplexed output samples that is simultaneously representative of two or more receive beams. A coefficient generator supplies the delay coefficients to the time multiplexed delay circuit in each of the processing channels.

Subarray configurations for digital beamforming with low sidelobes and adaptive interference suppression

Abstract: The paper investigates how subarrays in a large phased array should be arranged. The aim is to form sum and difference beams with low sidelobes with and without adaptation against external interference. At each array element phase shifting and amplitude tapering for one beam with low sidelobes is assumed. The other beams (e.g. difference beams) have to be formed digitally at the subarray outputs. Problems with grating lobes are considered.

Control of the necrosed tissue volume during noninvasive ultrasound surgery using a 16‐element phased array

Abstract: Focused high‐power ultrasound beams are well suited for noninvasive local destruction of deep target volumes. In order to avoid cavitation and to utilize only thermal tissue damage, high frequencies (1–5 MHz) are used in ultrasonic surgery. However, the focal spots generated by sharply focused transducers become so small that only small tumors can be treated in a reasonable time. Phased arrayultrasound transducers can be employed to electronically scan a focal spot or to produce multiple foci in the desired region to increase the treated volume. In this article, theoretical and experimental studies of spherically curved square‐element phased arrays for use in ultrasonic surgery were performed. The simulation results were compared with experimental results from a 16‐element array. It was shown that the phased array could control the necrosed tissue volume by using closely spaced multiple foci. The phased array can also be used to enlarge a necrosed tissue volume in only one direction at a time, i.e., lateral or longitudinal. The spherically curved 16 square‐element phased array can produce useful results by varying the phase and amplitude setting. Four focal points can be easily generated with a distance of two or four wavelengths between the two closest peaks. The maximum necrosed tissue volume generated by the array can be up to sixteen times the volume induced by a similar spherical transducer. Therefore the treatment time could be reduced compared with single transducer treatment.

Cost effective geosynchronous mobile satellite communication system

Abstract: A satellite communication system including one or more satellites (Figure 3) in geosynchronous orbit and inclined at a predetermined angle greater than 0° relative to earth, a preferred angle being about 28.5° for full earth coverage, there is a constellation of satellites. Each satellite has a multi-element phased array antenna (RL and FL) and transmit and receive circuits (Figure 10) selectively connected to said multi-element phased array antenna for providing spatially discriminated spot radiation beams on the earth's surface, and a steerable spaced/ground antenna and transmitter-receiver circuitry connected thereto. At least one gateway ground terminal (Figure 2) having means for performing all spacecraft command and control, including uplink phasing of said phased array antenna for directive satellite transmissions to desired user locations.

High density integrated ultrasonic phased array transducer and a method for making

Abstract: The present invention discloses a high density integrated ultrasonic phased array transducer and method for making. The high density integrated ultrasonic phased array includes a backfill material having an array of holes formed therein. Each of the holes are separated a predetermined distance apart from each other and have a predetermined hole depth. Each of the holes contain a conducting material deposited therein forming a high density interconnect with uniaxial conductivity. A piezoelectric ceramic material is bonded to the backfill material at a surface opposite the array of conducting holes. Matching layers are bonded to the piezoelectric ceramic material. The surface opposite the array of conducting holes is cut through a portion of the matching layers, the piezoelectric ceramic material, and the backfill material, forming an array of isolated individual elements each having multiple electrical connections therein.

Cancellation of diffuse jammer multipath by an airborne adaptive radar

Abstract: Airborne surveillance radars need to operate in an environment that can include the presence of ground clutter, standoff jammers, and diffuse jammer multipath. It is demonstrated here that a phased-array radar that employs adaptive spatial degrees of freedom, plus two different sets of adaptive temporal degrees of freedom can effectively cancel the aforementioned interference to an acceptable level. The two different sets of temporal taps required for each antenna element consist of one set spaced by the pulse repetition interval, so as to cancel ground clutter, and another spaced by about one-half of the reciprocal of the radar bandwidth, so as to cancel the diffuse jammer multipath which may enter through the main beam of the radar, as well as its sidelobes. Using the ideal covariance matrix, a simulation has been developed, and the necessary conditions for cancellation are analyzed and discussed. It is also shown that the cancellation can be performed either with the antenna elements or a set of beams, but that the beam space approach requires fewer space-time degrees of freedom for nearly the same level of cancellation as the element space approach. >

Benchmark problem for beam pointing control of phased array radar against maneuvering targets in the presence of ECM and false alarms

Abstract: This paper extends an earlier benchmark problem for beam pointing control of a phased array radar to include the effects of false alarms and ECM. Multiple waveforms are included in the benchmark problem so that the radar energy can be coordinated with the tracking algorithm. The ECM includes a standoff jammer broadcasting wideband noise and targets attempting range gate pull off. The paper presents the radar model, the ECM techniques, the target scenarios, and performance criteria for the benchmark problem.

Personal beam cellular communication system

Abstract: A cellular communication system is provided for transmitting a large number of highly directive personalized communication beams throughout an original geographic cell of the cellular communication system. The system advantageously utilizes a phased array antenna positioned at a center location of the cell in conjunction with a spread spectrum communications method which includes code division multiple access techniques for increasing user capacity. Each of the communication beams represents user signals assigned to specific users located within the original geographic cell and are adjustable in the user's directions. The total number of the communication beams may equal the number of users within the cell. An omnidirectional antenna is positioned in close proximity to the center location of the cell for transmitting and receiving an omnidirectional communication beam for communication with users located within approximately one half of a mile of the center location. A plurality of digital beam forming networks are employed for feeding the phased array antenna with the user signals forming the personalized communication beams.

New uniplanar transitions for circuit and antenna applications

Abstract: New uniplanar microstrip-to-slotline, microstrip-to-coplanar strips (PS) and microstrip-to-coplanar waveguide (CPW) transitions for MIC/MMIC and slotline antennas for phased array applications are described. Such transitions are compact and suitable to be used in an open environment inside a package or a multichip module. The transitions share the concept of using a balun which consists of two microstrip lines connected to a slotline through a pair of coupled microstrips. In this paper, the transitions are studied theoretically using the Finite Difference Time Domain (FDTD) technique and measured experimentally using an HP8510C Network Analyzer. For a back-to-back microstrip-to-slotline transition, an insertion loss of less than 1.3 dB per transition is achieved over a 49% bandwidth with a minimum of 0.6 dB around the design frequency.