Showing papers on "Phased array published in 1991"

High-speed ultrasound volumetric imaging system. I. Transducer design and beam steering

Abstract: Transducer design and phased array beam steering are developed for a volumetric ultrasound scanner that enables the 3-D visualization of dynamic structures in real time. The authors describe the design considerations and preliminary evaluation of a high-speed, online volumetric ultrasound imaging system that uses the principles of pulse-echo, phased array scanning with a 2-D array transducer. Several 2-D array designs are analyzed for resolution and main lobe-side lobe ratio by simulation using 2-D fast Fourier transform methods. Fabrication techniques are described for 2-D array transducer. Experimental measurements of pulse-echo point spread responses for 2-D arrays agree with the simulations. Measurements of pulse-echo sensitivity, bandwidth, and crosstalk are included. >

The first demonstration of an optically steered microwave phased array antenna using true-time-delay

Abstract: The concept of true-time-delay steering for phased array antennas and its advantage over phase shifters in broadband applications are described with particular emphasis on the potential advantages offered by fiber-optic delay lines. The system architecture of the phased array antenna and the design and performance of the fiber-optic time-shifter networks in the antenna are described. The radiation patterns of the phased array antenna at L and X bands are presented. Using semiconductor laser switching to implement the delay times, the absence of beam squint in the antenna pattern and its frequency was switched from L to X band is demonstrated. >

Millimeter-wave design of wide-band aperture-coupled stacked microstrip antennas

Abstract: K-band aperture-coupled stacked microstrip antennas are studied and numerical results based on the solution of integral equations solved in the spectral domain are presented. The effects of varying physical parameters of the structure are investigated with the goal of designing millimeter-wave wideband microstrip antennas. Antennas with different characteristics are then analyzed and compared with experimental data. Bandwidths in excess of 20% are obtained and applications to phased array antennas are discussed. >

Volume imaging with MR phased arrays

Abstract: A volume MR phased array was constructed with two coils placed anteriorly and two coils posteriorly. Data acquired simultaneously from the four coils on a phantom were combined into a single image having a signal-to-noise ratio 80% better than that from the body coil. Additional comparisons of the four-coil phased array with a two-coil phased array and a Helmholtz pair having the same overall dimensions show how variations of signal amplitude and phase in the individual coils affect the composite SNR. Images of the male and female pelvis demonstrate how the improved SNR can be used to reduce the number of excitations, decrease the field of view, increase the echo time, or reduce the slice thickness. © 1991 Academic Press. Inc.

A spherical-section ultrasound phased array applicator for deep localized hyperthermia

Abstract: Computer data are presented for a nonplanar phased-array proposed as an applicator for deep, localized hyperthermia. The array provides precise control over the heating pattern in three dimensions. The array elements form a rectangular lattice on a section of a sphere so that the array has a natural focus at its geometric center when all its elements are driven in phase. When compared to a planar array with similar dimensions, the spherical-section array provides higher focal intensity gain. The relative grating-lobe level (with respect to the focus) is lower for scanned foci synthesized with this array (compared to a planar array with equal center-to-center spacing and number of elements). The spherical-section array has been simulated for use as a spot-scanning applicator as well as an applicator producing directly synthesized heating patterns. >

Null steering in phased arrays by controlling the element positions

Abstract: Null steering methods usually involve costly and complicated amplitude and/or phase control systems. A technique is presented for null steering based on the element position perturbations. The technique frees the phase shifters to be used solely for steering the main beam toward the direction of the desired signal. It also removes the limitations of the other techniques by independently steering the main beam and the nulls to arbitrary independent directions. This technique is also capable of obtaining sidelobe cancellation and wideband signal rejection. >

Linear conformal antenna array for scanning near end-fire in one direction

Abstract: A linear conformal array antenna consisting of double-ridged waveguide elements which are all tapered in the E-plane or the H-plane. The array of waveguide elements is fed by a Gent lens whose amplitude and phase characteristics can be adjusted to cause the waveguide element array to produce a desired radiation pattern. The linear array antenna, which has been tapered in the E-plane, can be operated to scan an electromagnetic endfire beam in one predetermined direction with a maximum scan loss of 3 dB. The array of waveguide elements can be substantially conformal with the fuselage of an airborne craft carrying the linear array antenna, thereby reducing aerodynamic drag and radar cross section. The linear array antenna has a bandwidth that is greater than an octave wide.

Practical Phased Array Antenna Systems

Abstract: Electronic scanning radar systems (ESRS) design and architecture antenna array fundamentals Antenna array fundamentals phased array elements array feeds case study - design of air defence ESRS compact, constrained feed phased array for AN/SPY-1 limited scan arrays limited scan arrays computer control of a multifunction radar computer control of a multifunction radar.

Two-dimensional optical architecture for time-delay beam forming in a phased-array antenna

Abstract: We propose and experimentally demonstrate a new two-dimensional optical architecture based on polarization switching by N spatial light modulators that provides 2N time delays to a phased-array antenna of p × p radiating elements. Moreover the 0 to 2π phase of the microwave signals is optically controlled by a liquid-crystal spatial light modulator that operates in the birefringent mode. The microwave signal originates from the coherent detection of a dual-frequency laser beam obtained with an acousto-optic frequency shifter. Preliminary experimental results obtained at a microwave frequency f = 1.85 GHz are presented.

Synthetic aperture ultrasonic imaging system using a minimum or reduced redundancy phased array

Abstract: A synthetic aperture ultrasonic imaging system for imaging a target with a resolution limited by a designated aperture. A phased array of nonuniformly spaced ultrasound transducers having an average inter-transducer spacing which is greater than a λ/2 Nyquist spacing for the transducers is used for imaging in a manner so as to either obtain a desired point spread function which is unattainable by a single image taken by the nonuniformly spaced transducers or to provide coarray equivalence to a phased array of transducers which are uniformly spaced at the λ/2 Nyquist spacing for the designated aperture. Coarray equivalence makes possible the technique of applying amplitude weightings to each of the nonuniformly spaced ultrasound transducers during transmit and receive modes and by forming a number of component images which when added together form a sum image substantially equivalent to a single image formed by a scan beam of the uniformly spaced transducers with the designated aperture. The complex values of the resulting component images are then added on a point by point basis, preserving phase, such that a point spread function of the sum image is substantially equivalent to the desired point spread function of the single image formed by the uniformly spaced transducers with the designated ape STATEMENT OF GOVERNMENT INTEREST This invention was made with government support under contract N00014-89-J-1538 awarded by the Department of the Navy. The government has certain rights in the invention.

Plasma reflectors for electronic beam steering in radar systems

Abstract: The author describes investigations into methods of generating a planar plasma for use as a reflector for radar waves. The use of the plasma reflector could allow electronic beam steering at frequencies above what is generally viable for phased arrays. Three aspects of the planar plasma production are investigated: localization of the plasma, main plasma production, and long-term viability of the system. Possible applications include ship-based antennas at X-band, airborne antennas at 94 GHz, and space-based antennas at 60 GHz. The author discusses system considerations for the three potential radar configurations. Results and potential small-scale experiments to test various aspects of the concept are discussed. >

Transmit/receive module technology for X-band active array radar

Abstract: Phased array radar system developments using X-band transmit/receive (T/R) module technology are summarized. Requirements are developed from systems concepts for fighter aircraft radar applications. Factors influencing system performance are discussed in terms of the allowable tradeoffs that must be considered for deployable systems. T/R module architectures are investigated in light of the system derived performance requirements. These module requirements are reduced to the individual circuit function level, and examples of circuits developed to meet these requirements are presented. Critical T/R module technologies are discussed in view of the latest developments in microwave active and control devices, manufacturing assembly processes and equipment, package materials and fabrication processes, and test automation. Module developments during the past 25 years are discussed chronologically and described in terms of the performance characteristics attained. Test requirements unique to module integration and aperture-level performance verification are highlighted. Module price targets are derived from affordability constraints imposed by the fighter aircraft radar application. >

Phased array for optical beam control

Abstract: An optical beam scanner incorporating an array of beam deflection elements commonly controlled to steer an optical beam impingent on the array is described. The beam steering elements are arranged in the array as individually controlled elements and the deflection of the beam is accomplished by setting the phase tilt and the phase offset of each element according to a calculation which removes modulo 2π phase shift from the required position relative to a flat plane. Thus, the array elements can be thin and need only supply about 2 radians of phase shift. These elements may be incorporated in a planar array using beam deflection elements such as liquid crystal beam deflectors by choosing a drive scheme representing either a blazed array or a flat piston array. Operation may be designed for a large range of light wavelengths and the system may efficiently accommodate a combination of the blazed and flat piston techniques to obtain beam deflection characteristics otherwise unavailable by the exclusive use of each individual technique. By use of the liquid crystal phased array approach, rapid, high accuracy, large area beam deflection is possible without the necessity of any moving parts and with low power drive requirements. Phased arrays of the type described above may be arranged in successive parallel planes with a common beam axis to provide two-dimensional beam deflection.

Optoelectronic wide bandwidth photonic beamsteering phased array

Abstract: A transmit/receive circuit for each of the antenna elements of a radar phased array including an optical fiber true time delay circuit responsive to an electrical RF signal for providing an optical signal having a controlled time delay, an optical fiber for propagating the time delay controlled optical signal, an optical detector circuit responsive to the propagated time delay controlled optical signal for providing a time delay controlled electrical signal, transmit circuitry responsive to the time delay controlled electrical signal for providing to the associated antenna element a transmit signal based on the time delay controlled electrical signal, and receive circuitry responsive to the time delay controlled electrical signal and the signal received by the associated antenna element. A first RF switch selectively couples the time delay controlled electrical signal to the transmit circuit during transmit times, and to the receive circuit during receive times; and a second RF switch couples the associated antenna element to the transmit circuit during transmit times, and to the receive circuit during receive times. The receive circuit further includes analog-to-digital conversion circuitry whose sample timing is controlled so as to provide for time alignment of the received signal relative to the received signals of the other transmit/receive circuits of the phased array. Alternatively, such time alignment is provided pursuant to processing of the sampled receive signals from the transmit/receive circuits of the phased array.

Ultra-wideband beamforming in sparse arrays

Abstract: Transient radiated fields caused by impulsively excited apertures and aperture response caused by incident impulsive waves has been the subject of considerable research in acoustics. This research is also of importance to wideband radar. Medical ultrasound steered phased arrays use transmitted pulses consisting of from one to three cycles of a damped sinusoid, which is similar to certain ultra-wideband radar systems. Related studies applied to wide-band radar transmitting a single cycle of a sine wave indicate that it may be possible to construct a steered phased array radar with ultra high resolution using very sparse array apertures. In narrowband phased arrays, grating lobe considerations require that the array elements be placed close together. In contrast, very sparse, utra high resolution wide band arrays may be constructed without incurring grating lobe problems.

Beamforming structure for modular phased array antennas

Abstract: A combination of doubly folded parallel plate beam combiners or dividers, configured to produce a desired composite beam for use in arrays of antenna elements. The doubly folded combiner or divider functions to expand a transmitted beam, or contract a received beam, in one selected plane. In a transmit mode, a single beam can be expanded first in one direction by a first divider, then expanded in a perpendicular direction by a stack of additional dividers coupled to the first. Optional phase shifting circuits provide beam steering as desired. Second and other additional beams can be processed in the same manner, to produce a composite output of multiple beams for transmission by an antenna array. Another aspect of the invention involves the use of a beam forming structure of this type in conjunction with an array of transmit/receive microwave modules providing amplification and phase shifting functions, and an array of printed circuit antenna elements. With appropriate phase shifting controls, a composite beam transmitted or received by the array or antenna elements can be steered independently in azimuth and elevation, using much less complex control circuitry than a conventional phased array antenna system.

Reversible time delay beamforming optical architecture for phased-array antennas

Abstract: A phased array antenna system has optical architecture comprising free space delay units and associated spatial light modulators compatible for operation with temporally incoherent or coherent laser light to produce signals having selected time delays to actuate antenna elements of an antenna array to transmit electromagnetic radiation at a selected beam angle from the phase array. The same optical architecture is used to process electromagnetic signals detected by the antenna array to produce an output signal for display or processing which corresponds to the radiation detected at the selected beam angle.

Experimental evaluation of a prototype cylindrical section ultrasound hyperthermia phased-array applicator

Abstract: A prototype 64-element, 75 degrees cylindrical-section ultrasonic phased-array hyperthermia applicator has been designed and constructed. The ability of this applicator to focus ultrasonic energy at its geometric focus is verified in a water medium. The array is then driven by excitation vectors obtained using the pseudoinverse pattern synthesis method to generate shifted-focus and multiple-focus field patterns. Experimental results of single and multiple-focus patterns at 500 kHz are given and are in good agreement with theory. The results indicate that the main beam in single-focus patterns is generally insensitive to errors in the phases and amplitudes of the particle velocities of the array elements. The effect of such errors is largely exhibited in the sidelobes which, for all practical purposes, remain at levels acceptable for hyperthermia. This is true for both the geometric focus and shifted foci. >

Modulation of phased-array semiconductor lasers at K-band frequencies

Abstract: The possibility of phase locking the lateral modes of a multiple-emitter semiconductor-laser phased array by modulating at the beat frequency of the lateral modes is presented. A rate equation model of a twin-emitter array is introduced and used to find the response of the optical output of the array to small sinusoidal modulations of the injection current. In-phase modulation of the emitters is found to be ineffectual, while modulating the emitters 180 degrees out of phase extended the responsivity well beyond the relaxation oscillation frequency to approximately the frequency associated with the rate of photon exchange between the coupled emitters. The rate equations were numerically integrated for several cases of interest to evaluate the stabilizing effect of strong modulation (entrainment). >

Dielectric flare notch radiator with separate transmit and receive ports

Abstract: A dielectric antipodal flared notch radiator (50) with separate transmit and receive ports (72,76) for phased array and active array antennas. A circulator (80) is integrated directly to the broadside coupled-strip transmission line portions (78,88) of the antipodal flared notch radiator without the use of baluns. The look-in impedance of the radiator element is improved as a result of the circulator and lack of a balun. By sandwiching the antipodal flared notch between two additional layers of dielectric (54,56), the device can be made a building block for broadband active array antennas.

Ultrasonic imaging system with multiple, dynamically focused transmit beams

Abstract: A phased array sector scanning (PASS) ultrasonic imaging system produces a steered transmit beam with an array of transducer elements that are driven with separate carrier frequencies. A receiver forms the echo signal into a receive beam steered in the same direction as the transmit beam and is dynamically focused. A transmit beam processor Fourier transforms this receive beam to produce a signals corresponding to the separate carrier frequencies which can be delayed to retrospectively dynamically focus the transmit beam or alter the direction in which it is steered.

Adaptive nulling hyperthermia array

Abstract: A hyperthermia array uses adaptive nulling with non-invasive auxiliary probes to reduce the electric field intensity at selected positions in the target body while maintaining a desired focus at a tumor thereby avoiding or reducing the occurrences of "hot spots" during ultrasonic or R.F. hyperthermia treatment. A hyperthermia applicator has an annular phased array of electric field radiators coupled to a source of electric radiation through a controllable transmit weighting network to control the phase and amplitude of the electric field radiation transmitted. The transmit weighting networks respond to feedback signals from a controller coupled to ele GOVERNMENT SUPPORT The invention described herein was supported in whole or in part by Contract No. F19628-90-C-0002 from the United States Air Force.

Fault isolation in a Butler matrix fed circular phased array antenna

Abstract: A method for monitoring a phased array antenna system to determine the existence of faulty components in the system and the location of such components in the system. More particularly, the invention relates to a Butler matrix-fed circular phased array antenna system wherein an individual one of the plurality of columns of the array which is faulty can be identified by comparison of a measured amplitude value to a predetermined level.

Optimization of the intensity gain of multiple-focus phased-array heating patterns.

Abstract: A new technique for enhancing the intensity gain at the focal points in multiple-focus patterns is introduced. The new technique is shown to be effective in reducing the interference typically associated with multiple-focus patterns. This reduction in interference patterns allows multiple-focus scanning to generate highly localized heating. Simulation results indicate that multiple-focus scanning not only provides an alternative to single-focus scanning, but also achieves better localization in the heating pattern. The maximization of intensity gain of multiple-focus heating patterns significantly reduces the pre-focal-depth high-temperature regions that can be caused by single-focus scanning. This is shown by computer simulation of a two-dimensional cylindrical-section array (CSA2D) as a heating applicator. Two series of simulations are presented in which different scan trajectories were used to therapeutically heat a small deep-seated target volume. In every case the heating pattern was generated using ...

Novel phased array optical scanning device implemented using GaAs/AlGaAs technology

Abstract: A novel type of optical beam scanning device based on the same principle as a phased array radar has been made and demonstrated. This phased array optical scanning device consisted of a uniformly illuminated array of ten closely spaced, single mode GaAs/AlGaAs electrooptic waveguides, each of which was individually addressed to give more than 2π radians of optical phase control. This gave a line of ten point sources of light on a 3 μm pitch at the output face of the array. By independently phase shifting these light sources the output wavefront was controlled to scan a 2° wide beam through 20° in the far field.

Time domain filtering for NMR phased array imaging

Abstract: A method and apparatus for combining NMR response data of a sample from a plurality of closely spaced RF receiver coils of an NMR phased array in the time domain to form a composite NMR image wherein each of the RF receiver coils receives a different respective one of a plurality of NMR response signals, each of which is evoked from a portion of the sample within a field of view of a respective one of the receiver coils. The response signals are conditioned to develop a plurality of data point signals corresponding to the magnitude of each of the respective response signals from each of the receiver coils at successive time intervals. The data point signals are convolved by a time domain representation of a field map of the respective one of the receiver coils generating the corresponding one of the response signals. The convolved signals are combined on a time domain point-by-point basis to produce a time domain representation of the composite NMR image of the sample.

Dynamic transmit focusing of a steered ultrasonic beam

Abstract: A phased array sector scanning (PASS) ultrasonic imaging system produces a fixed focus, steered transmit beam with an array of transducer elements. A receiver forms the echo signals received from an ultrasonic energy reflecting object at the array elements into a receive beam steered in the same direction as the transmit beam and dynamically focused. A midprocessor in the receiver makes corrections to the receive beam samples to offset errors caused by the transmit beam being out of focus at all but its fixed focal range.

Transmit/receive time-delay beam-forming optical architecture for phased-array antennas

Abstract: A robust, compact, and efficient time-delay beam-forming optical architecture is introduced that operates in both the antenna transmit and receive modes.

Opto-electrical transmitter/receiver module

Abstract: A fiber optic transmitter/receiver module used for controlling multi-axis beam steering of each individual radiating element in a phased array antenna and which is an integral part of a reconfigurable fiber optic corporate feed concept. In the receive mode of operation an incoming signal is captured, amplified and converted into the light domain by means of optical heterodyning. The relative phase and amplitude of the signal would be controlled by optically adjusting the amplitude and phase of a local oscillator. The local oscillator is sent to each fiber optic transmitter/receiver module. In the transmit mode of operation a signal for transmission which is in the light domain is down converted into the electromagnetic domain using optical mixing techniques. Once again, the relative phase and amplitude of the transmission signal would be controlled by the local oscillator. The beam steering capability is accomplished by configuring the local oscillator for each element of the antenna with a specific amplitude and phase.

Multiband shared aperture array antenna system

Abstract: A lightweight phased array antenna systems that is conformable to an aircraft fuselage combines air-filled cavity-backed slots with printed circuit elements for operation in two or more frequency bands. The printed circuit elements are separated from a conductive ground plane in which the slots are cut by a dielectric honeycomb material. The slots and printed circuit elements are individually excitable by a multiband feed network and transmit/receive modules for operation in the UHF band and S band or L band, respectively.