Showing papers on "Phased array published in 1983"

Beam Steering with Linear Arrays

Abstract: The principles and techniques of real-time imaging with phased array ultrasound scanners are reviewed. Topics include 1) the geometric optics of beam steering and focusing with a linear array in the transmit and receive modes; 2) limitations on image data acquisition due to ultrasound propagation velocity; 3) optical diffraction theory for linear arrays including effects of amplitude grating lobes. Limitations on the image quality of phased array imaging systems are also discussed, including 1) nonideal response of array transducers; 2) target ambiguities caused by phase error grating lobes; 3) refraction errors; 4) delay line design. Finally, an analysis is presented of current techniques for improving ultrasound image quality using phased array methods including phase compensation, spatial compounding, frequency compounding, and parallel processing.

Decoupled Kalman filters for phased array radar tracking

Abstract: Kalman filters have been used in numerous phased array radars to track satellites, reentry vehicles, and missiles. This paper considers the design of these filters to reduce computational requirements, ill-conditioning, and the effects of nonlinearities. Several special coordinate systems used to represent the Kalman filter error covariance matrix are described. These covariance coordinates facilitate the approximate decoupling required for practical filter design. A tutorial discussion and analysis of ill-conditioning in Kalman filters is used to motivate these design considerations. This analysis also explains several well-known phenomena reported in the literature. In addition, a discussion of nonlinearities and methods to mitigate their ill effects is included.

Adaptive clutter suppression for airborne phased array radars

Abstract: The problem of clutter suppression is more serious for airborne than for ground-based radars because the ground returns become Doppler coloured owing to platform motion. Therefore the clutter power depends on both the azimuth and the Doppler frequency. Such two-dimensional spectra can only be suppressed by two-dimensional filters, which require sampling of the echo field in both space and time. This is verified by a phased array radar using coherent pulse trains. The platform motion causes of the clutter background to change with time, and any change of the platform velocity results in a change of the Doppler characteristics of the clutter retunrs. Therefore the two-dimensional filter has to be adaptive. The paper presents some new results on optimum adaptive clutter suppression. For comparison, a suboptimum approach (beamformer plus adaptive temporal filter) is presented. It turns out that the favourable properties of the optimum space-time clutter filter can hardly be achieved by any suboptimum subtitute.

Ultrasonic endoscope having elongated array mounted in manner allowing it to remain flexible

Abstract: The invention is a fiber-optic endoscope which has an elongated ultrasonic array, such as a linear array or a phased array. The array is mounted on either the distal portion of the bending section (not under operator control) portion of the endoscopic tube or on the proximal portion of bendable portion of the tube. Thus, the present invention includes both a fiber-optic endoscope and an ultrasonic transducer. Yet, the presence of the ultrasonic transducer does not interfere with the operation of the placement of the fiber-optic probe.

Multifrequency HF radar observations of currents and current shears

Abstract: Techniques have been developed for using high-frequency (HF) surface-wave radar to measure ocean currents and vertical current shears in the upper 1 or 2 m of the ocean surface. An HF radar can precisely measure the phase velocity and direction of propagation of ocean waves whose wavelength is one.half the radar wavelength. In the absence of a current, the speed of the waves is given by the still-water dispersion relation. An underlying current will modify this speed. The radar measures the actual phase velocity through a Doppler shift, and the wavelength of the ocean wave is known through the first-order Bragg scattering relation, so a difference between observed and theoretical stillwater phase velocity can be calculated. In addition, longer ocean waves are affected by currents at deeper depths than are shorter ocean waves. By measuring the phase velocity at several different wavelengths, it is possible to measure a vertical current shear in the top 1 or 2 m of the ocean surface. This is a measurement that is very difficult to make by any other means. A portable coherent pulsed-Doppler HF radar system was developed at Stanford and used in several experiments, both on land on the California coast and on board a ship during the Joint Air-Sca Interaction (JASIN) experiment. The land-based experiments demonstrated that a current could be measured by an HF radar, and that its value agreed well with that measured by in-situ drifting spar buoys. In addition, there was evidence of a vertical current shear, both from the radar measurements and from the buoy measurements. The JASIN experiment was an attempt to apply these techniques to the measurement of surface current and current shear in the open ocean. The radar system was installed on board a ship, along with a receiving antenna consisting of a steerable phased array of eight wide-band loops. The steerable antenna was quite rugged and performed as expected. It produced antenna patterns consistent with the physical aperture of the array. The wind velocity during the JASIN experiment was quite low, so wind- and wave-generated currents were quite small. Nevertheless, there is some evidence of a current shear. Its magnitude is small and near the resolution limit of the radar, but it appears to be somewhat higher than estimates based on either the wind or wave conditions alone, but less than the estimates based on the sum of the two components.

Phased array inspection of cylindrical objects

Abstract: A first array (A) of ultrasonic transducers transmits ultrasonic shear waves circumferentially around an examined cylindrical object (110). A second array (B) transmits ultrasonic shear waves axially along the examined object. Triggering pulses from a triggering amplifier (22) are switched by a multiplexer (24) to each individual transducer of the first and second arrays. As one of the transducers assumes the role of a transmitting transducer and transmits an ultrasonic wave, the other transducers of the first and second arrays assume a receiving mode to receive reflected ultrasonic components. A wave travel timer (26) measures the duration for an ultrasonic wave to be transmitted from the transmitting transducer to a defect and for a reflected component to propagate from the defect to the receiving transducer. A microprocessor (20) tri-angulates or otherwise computes the location and orientation of a reflective defect from the measured travel time, the spatial relationship of the transmitting and receiving transducers, and the direction of propagation of the transmitted ultrasonic wave.

A new technique for reducing radar response to signals entering antenna sidelobes

Abstract: A new technique for reducing a radar's response to undesired signals entering a radar's sidelobes is described and analyzed theoretically. This technique involves moving a phased array antenna's phase center to Doppler shift sidelobe signals out of the radar receiver's passband.

Design of a Simplified Delay System for Ultrasound Phased Array Imaging

Abstract: A novel technique for implementing the dynamically vari- able delay system, required for electronic sector scanning in ultrasound phased-array imaging equipments, has been recently introduced. The technique is based on separate and independent processing of the car- rier and of the envelope of the echo pulses. Carrier phasing is accom- plished by electronic phase-shifters, while envelope delay is varied by delay lines. This latter function, however, can be performed using dw Crete delays in increments much larger than those required by previous techniques. Extensive computer simulations of the array directivity pattern have been performed to evaluate the effect of a coarse delay quantization. Based on the simulation results, the design of a delay sys- tem exhibiting a dramatic simplifkation over alternative techniques is described.

Dual band phased antenna array using wideband element with diplexer

Abstract: A dual band, phased array antenna especially adaptable for tactical radar capable of performing search, track and identification in a hostile jamming environment The dual band array antenna is essentially two antennas sharing a common antenna aperture The two antennas possess separate feed system and beam steering control Thus, the beams for each frequency band can be steered independently and simultaneously This design utilizes an ultra-wide band radiating element which can operate over approximately an octave bandwidth encompassing two adjacent microwave bands In particular, the dual band signals can be received efficiently by the radiating element A dual band coaxial-to-waveguide transition can be used to carry the signals to a diplexer The dual band signals are separated at the diplexer and can be processed in separate feed networks The advantages of this dual band phased array technique include not only good impedance characteristics but also the absence of grating lobe formation and cross coupling problems

Phased-array sound pickup apparatus

Abstract: A phased-array sound pickup apparatus has an array of directional microphones having individual directivity patterns equally oriented in a given direction. The directivity patterns of the microphones combine into the main lobe of the array. A plurality of variable delay circuits are connected to be responsive respectively to individual signals from the microphones for providing incremental delays to the individual signals and combining the delayed signals for delivery as an output of the apparatus. A delay control circuit is coupled to the variable delay circuits for generating a delay control signal for controlling the amount of the incremental delays to cause the main lobe to be steered at an angle to the given direction as a function of the delay control signal.

Phased-array sound pickup apparatus having no unwanted response pattern

Abstract: In a phased-array sound pickup apparatus microphones are divided into a first and second subarrays, the microphones of the first subarray having individual unidirectional response patterns oriented on one side of the normal to the array and the microphones of the second subarray having their response patterns oriented on the other side of the normal so that the array's main lobe assumes different orientation from the orientation of the microphone's individual response patterns so that the array's unwanted back lobe falls outside of the microphone's response patterns. The microphones may be grouped into a plurality of pairs and the signals from the paired microphones are mixed so that different individual response patterns are generated in correlation with the array's main front lobe to cause the unwanted back lobe to occur outside of the individual response patterns.

Focused array hyperthermia applicator: Theory and experiment

Abstract: Recent research has shown that treatment of tumors with localized heat (42 - 45 degrees Celsius) can cause partial or even complete tumor regression. Heating with microwave energy may prove to be a viable clinical procedure. A promising approach to microwave hyperthermia applicator design is to use phased array antennas to rapidly scan an arbitrary tumor volume with a minimal diameter beam or heating spot.

Coupled amplifier module feed networks for phased array antennas

Abstract: A beam-steering feed network for use with linear and planar phased-array enna systems which includes a phase divider system for producing a plurality of incrementally phased IF signals. The phase divider system includes a plurality of coupled amplifier phase divider modules coupled together to form a network. The network is coupled to receive at least two boundary signals having different phase angles. The phase angle difference between the boundary signals is divided by the phase divider modules in the network. Each module produces an output signal having a phase angle differing from that of the output signals of the immediately adjacent modules in the network by a phase angle gradient. The system thus divides the phase angle difference between the boundary signals into a plurality of incrementally phased output signals.

Phase-only optimization for the generation of wide deterministic nulls in the radiation pattern of phased arrays

Abstract: Some analytical and experimental results of the phase-only optimization of each array element for the generation of wide deterministic nulls in the sidelobe region of the radiation pattern of a phased-array antenna are presented. The technique derives from the adaptive null-steering theory and is applied in the radar field to the spatial filtering of strong clutter echoes or jammers. A wide deterministic null has been realized in the elevation pattern of a phased-array antenna, with electronic scanning in elevation, without any hardware change; the calculated performances are compared to the measured data.

Optoelectronically switched phase shifter for radar and satellite phased array antennas

Abstract: This invention utilizes an opto-electronic matrix switch to select a set of fixed value phase shifters. Signals which are selectively phase shifted by this apparatus may be introduced into the signal path of each antenna element of a phased array antenna. In one embodiment the input signal is converted into an intensity modulated optical signal which is then split between paths of different length to provide different delays and hence different phase shifts. The matrix then selects a particular set of the phase shifted signals which are converted back to electrical signals and fed to the antenna array elements.

Method for tuning a phased array antenna

Abstract: During installation or maintenance of a phased array antenna system in which the transmission line to each element includes an adjustable phase shift device, it is required that the effective electrical lengths of the lines be adjusted to be equal, or alternatively that the phase errors be determined and stored as correction data for use during normal operation. One way of doing this is to phase modulate by ±90° the phase shift device of one element at a time, while applying a test signal to all elements. The signal is radiated by the array, received via a test antenna, and supplied to an envelope detector. If the element is out of tune, the envelope has different amplitudes at +90° and -90° of the modulation. The element is tuned by adjusting the length of its transmission line or the adjustment of its phase shift device to obtain a null at the amplitude detector. In an improved technique, to reduce certain errors, sum tuning is used, in which the ±90° phase modulation is applied to all of the phase shift devices, except for that of the element being tuned.

Radiation pattern computations for cylindrical-rectangular microstrip antennas

Abstract: Microstrip antennas may be mounted on spherical surfaces on some vehicles of practical interest such as missiles and satellites. One possible application, for example, might be to build phased array microstrip radiators on a spherical surface to give wide angle scan capability much like that of a Luneberg lens antenna. The cavity model method is used to obtain the electric field at the edge of the radiating patch. Then, the radiation field may be evaluated from the edge field for a given excitation current. A spherical-rectangular microstrip structure is studied. The study is based on the assumption that the thickness of the dielectric layer is much smaller than the radius of the ground sphere. Then, the radiation frequency for single mode radiation is defined and the radiation patterns for typical spherical-rectangular microstrip antennas are presented.

Dual space fed parallel plate lens antenna beamforming system

Abstract: A beamforming system for a linear phased array antenna system which can besed in a monopulse transceiver, comprising a pair of series connected parallel plate constrained unfocused lenses which provide a suitable amplitude taper for the linear array to yield a low sidelobe radiation pattern. Digital phase shifters are used for beam steering purposes and the unfocused lenses decorrelate the quantization errors caused by the use of such phase shifters.

Continuous ferrite aperture for electronic scanning antennas

Abstract: A radiating element (10) having a continuous aperture substantially greater than one half the center frequency wavelength for use in an electronically scanned phased array antenna operating in the range of 94 GHz. The new radiating element comprises a ferrite block (12) having a radiating aperture which measures 5 lambda by 5 lambda in contrast to the conventional discrete radiating element which measures one-half lambda by one-half lambda. A tapered magnetization (see lines 22) is applied to the continuous aperture ferrite block (12). The degree of phase shift can be varied by adjusting the slope of the tapered magnetization. This permits scanning of the continuous aperture pattern. When a plurality of such continuous aperture subarrays is used to form an antenna array (80 or 100), provision is made to adjust the phase at the center of each continuous aperture subarray with respect to the phase of the adjacent subarrays, thereby allowing scanning of the entire pattern of the phased array antenna (100).

Dual scan rate radar

Abstract: A dual scan rate radar system (DSR) including a phased array antenna, a tsmitter, a receiver and a control unit. Each rf pulse from the transmitter includes contiguous long-range and short-range pulses. The control unit adjusts the antenna so that the long-range pulse is transmitted into a slow beam at θ S and the short-range pulse is transmitted into a fast beam at θ F . The control unit also adjusts the antenna to receive the short-range pulse echos during a first part of the interpulse interval and the long-range pulse echos during a second part of the interpulse interval. The angles θ S and θ F are varied so that the slow and fast beam are scanned at dual rates R S and R F , respectively, where R S

Integrated modular phased array antenna

Abstract: A modular integrated multi-element phased array antenna. The antenna is comprised of a supporting structure having a plurality of slotted, ridged waveguide radiator elements longitudinally extending therein and a single series ridged waveguide feed structure, having a first and second plurality of waveguide channels formed therein. The feed structure is supported by at least a portion of the supporting structure and receives microwave energy from a source and then couples the energy to the first plurality of waveguide channels. The antenna is further comprised of a multi-element phase shifter module positioned in juxtaposition with the feed structure for receiving the microwave energy from each of the first plurality of waveguide channels. The phase shifted energy is coupled from the phase shifter module to each of the second plurality of waveguide channels. Means is also provided for coupling the phase shifted energy from each of the second plurality of waveguide channels to each of the waveguide radiator elements, whereby the phase shifted energy in the form of a desired microwave beam pattern is transmitted from the radiator elements to a desired location.

Means for aligning elevation beam pattern along an isodop in synthetic aperture mapping radar

Abstract: Using an electronically scanned phased array antenna, a technique is developed for aligning a broad elevation beam along an isodop for use in synthetic aperture mapping. A beam steering controller algorithm for practical implementation of the technique is described. Implementation is realized by means of a beam steering controller and the radar computer. The controller first finds the space stabilized row and column for a given phase shifter. A look-up table furnished by the radar controller provides a slope correction as a function of row. The slope is multiplied by the element column to give the correct linear phase function. This term is then subtracted from the term used to point the beam peak.

Monolithic millimeter-wave electronic scan antenna using Schottky barrier control and method for making same

Abstract: A millimeter-wave electronic scan, phased array antenna in a slotted dielectric waveguide having a semi-insulating core and at least one semi-conducting epitaxial layer. A controller affixed to the epitaxial layer is used to apply a bias voltage thereby varying the conductivity of the layer and influencing wave propagation in the guide to effect beam scanning.

The Performance of GaAs Lumped Element Phase Shifters at S and C Band

Abstract: The design and performance of an S-band analogue/digital phase shifter GaAs IC chip set, developed for use in a phased array radar transmitter, will be described. The circuits have been used to demonstrate successfully the feasibility of using GaAs IC technology in this application, at a frequency where the more conventional transmission line techniques cannot be used easily due to the large size of the circuit elements. The present circuits rely on the use of lumped components, to minimise the area of GaAs used. The extension of the techniques to higher frequencies (C-band) will also be discussed.

Two-dimensional imaging with a radio camera

Abstract: In the radio camera, adaptive control techniques self-cohere the antenna elements of a phased array, thereby permitting the system to be distorted and even time varying. By doing so, enormous antenna arrays can be constructed A two-dimensional (range-angle) radio camera imaging experiment is reported. A 39-m X-band (3-cm wavelength) array was formed on a cable strung between two towers, each 10 m high, on a hilltop. A pulsed microwave transmitter on the hilltop illuminated the vicinity of Phoenixville, PA, some 7 km distant. As the receiver was moved along the cable, echoes were recorded at random positions. The time-shared receiving array was highly distorted as well as time-varying, yet the radio camera processing produced nearly diffraction-limited images of three city blocks at a distance of 6.5 km in the town, and details of a power plant at a distance of 8.2 km. The use of two different pilot signals or beamforming sources for the self-synchronization process is demonstrated. One source is a corner reflector located in the town; the other is a target of opportunity located in the vicinity.

Element pattern approach to design of dielectric windows for conformal phased arrays

Abstract: Modal analysis is presented for the realized element gain E and H plane patterns for two-dimensional cylindrical arrays with a concentric dielectric sleeve. Numerical results indicate that a dielectric window in the near field of a conformal phased array may cause significant deterioration of the element pattern due to guided wave effects. If the window is inappropriately configured, this deterioration manifests itself in appearance of pronounced dips and of an excessive off-broadside ripple. A design method of dielectric windows for conformal arrays to reduce the guided wave effects is proposed. The method is validated by direct evaluation of the E and H plane element patterns for optimized window geometries.

Twin aperture phased array lens antenna

Abstract: A phased array lens antenna which includes a lens having two faces disposedubstantially at a right angle to each other. Transmit-receive modules which include phase-shifters are shared between the two lens faces. Two lens antennas positioned in back-to-back relationship about a ship superstructure scan 360°.

Phase insensitive detector for use in ultrasonic scanner and method

Abstract: Improved B-scan images are obtained in an ultrasonic scanner by means of a phase insensitive imaging system. Backscattered signals are detected by a phased array of detector elements. Signals from each detector element are full wave rectified, low pass filtered and are nonlinearly processed by power law compression. The compressed signals are summed and then expanded by an inverse power law function.

Phased array antenna

Abstract: A external feedback network (4, 5) for decreasing variations in a beam pointing angle of a scanning antenna array. A dedicated aperture manifold (4) is integral with the aperture (1) of the scanning antenna and provides a signal which represents the beam pointing angle. The signal is detected (13), decoded (15), and converted into digital data for averaging and processing by a central processing unit a (CPU). The processed data is then compared with a value stored in memory and any difference forms the basis of a correction signal. For application to a microwave landing system, the correction signal is used to adjust the start/stop time of the scanning commands of the antenna to remove the error without modifying the beam steering algorithm. A space-coupled monitor (6,7) may also be used independent of the feedback network to provide an alarm indication in response to any failure of the dedicated aperture manifold (4), the automatic stabilization circuitry (5) or the array system (1, 2, 8, 9, 11).