Showing papers on "Phased array published in 1994"

Adaptive transmitting antenna arrays with feedback

Abstract: We address the problem of transmitting multiple cochannel signals from an antenna array to several receivers so that each receiver gets its intended signal with minimum crosstalk from the remaining signals. In addition to the usual "information" mode, we propose a "probing" mode during which probing signals received at the mobiles are fed back to the transmitter. These probing signals are used to identify an unknown propagation environment, enabling the transmitter to form the necessary transmission beampatterns. >

Phased array antenna system including a coplanar waveguide feed arrangement

Abstract: The disclosure relates to a phased array antenna for microwave and millimeter wave applications, using either microstrip line, coplanar waveguide, or other construction techniques incorporating a solid dielectric transmission line. A continuously variable phase delay structure which is used to control the beam pattern of the phased array antenna can be applied to the construction of resonant frequency tunable coplanar waveguide antennas and impedance tunable quarter-wave transformers. A thin film of barium strontium titanate (Bax Sr1-x TiO3) or other nonlinear material such as PbZrx Ti1-x O3 (PZT), LiNbO3, etc. is deposited upon the coplanar waveguide, and/or the patch antenna element. The dielectric constant of the thin film can be made to vary significantly by applying a DC voltage to the thin film. The propagation constant of a transmission line is directly proportional to the square root of the effective dielectric constant (assuming a lossless dielectric). In an array of multiple antenna elements provided with the feed structure using the disclosed transmission lines, the direction of the resultant main beam of the array can be made to vary over a complete half-sphere with only two adjustable DC voltages applied to the dielectric thin films.

Phased array antenna system using polarization phase shifting

Abstract: A circularly polarized phased array antenna system for both reception and transmission applications includes a plurality of planar radiating (or receiving) elements, a switching matrix for each radiating element, a beamforming network and a transmit/receive module. Each planar element includes 4×N radially disposed segments that may be selectively connected with the four modes of a circularly polarized signal such that two opposing segments function as the two respective arms of a dipole radiating element and two orthogonal such dipoles function as a crossed pair of dipoles for receiving or transmitting the circularly polarized signal. The switching matrix and the beamforming network cooperate to determine the polarization phase of the radiating element by commutating the four modes of the circularly polarized signal to any four orthogonal segments of the radiating element. The polarization sense may be changed between right-hand and left-hand circular either within the bandforming network, or by causing the switching network to reverse the two signal modes connected across one of the dipoles. If N is greater than 1, then by electrically connecting up to N-1 nearby segments to thereby increase the effective angle subtended by each arm, the bandwidth may be increased while still permitting the radiating element's polarization phase to be determined in increments equal to the angle subtended by one segment; by selectively using either an odd or even number of segments to define the effective angle subtended by each dipole arm, the relative phase of that element may be determined in increments equal to half the angle subtended by one segment.

Blind estimation of multiple co-channel digital signals using an antenna array

Abstract: Proposes a novel approach for separating and estimating multiple co-channel digital signals using an antenna array. The spatial response of the array is unknown. The authors exploit the temporal structure of the digital signals to simultaneously determine the array response and the bit sequence for each signal. Uniqueness of the estimates is established for signals with BPSK modulation format. This new approach is applicable to an unknown array geometry and propagation environment, which is particularly useful in digital mobile communications. Simulation results demonstrate its promising performance. >

Reconstructions of phase contrast, phased array multicoil data

Abstract: We present a reconstruction method for phased array multicoil data that is compatible with phase contrast MR angiography. The proposed algorithm can produce either complex difference or phase difference angiograms. Directional flow and quantitative information are preserved with the phase difference reconstruction. The proposed method is computationally efficient and avoids intercoil cancellation errors near the velocity aliasing boundary. Feasibility of the method is demonstrated on human scans.

Array pattern nulling by element position perturbations using a genetic algorithm

Abstract: . t geneti- algorithm has been used for null steering in phased and :,daptive arrays. It has been shown that it is possible to steer the tray nul ls precisely to the required interference directions and to chieve ny prescribed null depths . A comparison with the results brained from the analytic anlution shows the advatages of using he genetic algorithm for null steering in linear array patterns. fntroduc ion: Nu :. steering in adaptive arrays can be achieved by element ,position perturbations [1 -3]. This technique is based on the assn ; sption. of. relatively smell element position perturbations so that r a analytic solution can be formulated . Results were given for displ tcemects of the elements both along , and normal to, the axis of Cu array . In this Letter , we report the use of a genetic algorithm (4) in the realisation of adaptive nulling by element position perturbations. The use of F. genetic algorithm removes the restrictions imposed on the array element displacements in order to obtain the linear analytic solution . The results presented show that it is possible to steer the array nulls precisely to the required interference dire Lions and to achieve prescribed null depths.

Phased array antenna analysis with the hybrid finite element method

Abstract: A new analysis technique for infinite phased array antennas was developed and demonstrated. It consists of the finite element method (FEM) in combination with integral equation radiation conditions and a novel periodic boundary condition for 3-D FEM grids. Accurate modeling of rectangular, circular and circular-coaxial feeds is accomplished by enforcing continuity between the FEM solution and several waveguide modes across an aperture in the array's ground plane. The radiation condition above the array is enforced by a periodic integral equation in the form of a Floquet mode summation, thus reducing the solution to that of a single array unit cell. The periodic boundary condition at unit cell side walls is enforced through a matrix transformation. That mathematically "folds" opposing side walls onto each other with a phase shift appropriate to the array lattice and scan angle. The unit cell electric field is expanded in vector finite elements. Galerkin's method is used to cast the problem as a matrix equation, which is solved by the conjugate gradient method. A general-purpose computer code was developed and validated for cases of open-ended waveguides, microstrip patches, clad monopoles and printed flared notches, showing that the analysis method is accurate and versatile. >

Benchmark problem for beam pointing control of phased array radar against maneuvering targets

Abstract: Presents a benchmark problem for tracking maneuvering targets. The benchmark problem involves beam pointing control of a phased array (agile beam) radar against highly maneuvering targets. A testbed simulation program that includes the effects of target amplitude fluctuations, beamshape, missed detections, finite resolution, target maneuvers, and track loss is described. Limits on the position and maneuverability of the targets are given along with descriptions of six target trajectories. The "best" tracking algorithm is the one that requires the minimum number of radar dwells while satisfying a constraint of 4% on the maximum number of lost tracks.

New stacked microstrip antenna with large bandwidth and high gain

Abstract: A new radiating element is presented, which can provide simultaneously a large bandwidth and high gain. It consists of four identical patches uniformly displayed within a rectangular aperture (2*2) and fed electromagnetically by a driven patch etched on a lower substrate. It is shown that a good coupling with the parasitic patches is obtained, causing a large bandwidth, and the resonance modes of each patch are excited in phase, giving a high gain.

Wideband interference suppressor in a phased array radar

Abstract: A phased array radar antenna uses time-steering subarray notch weightings to produce a wideband notch in the direction of interference for Electronic-Counter-Measure (ECM) interference suppression. A predetermined set of subarray notch weightings, each set being identical for each subarray, is stored in controllers each of which is coupled to a plurality of phase shifters and attenuators for feeding radiating elements of the antenna. Interference suppressors operate from a plurality of controllers to produce a subarray pattern having a notch in the direction of interference. Beamformers then combine outputs of all time-steering subarrays in the antenna so as to produce an antenna pattern having a wideband notch in the direction of interference.

Antenna array of radiators with plural orthogonal ports

Abstract: A phased array antenna (10A, 10B, 10C) is constructed of an array of radiators (24), each of which has a radiating aperture, a first port (26) and a second port (26). The first port introduces a first radiation with a first polarization, and the second port introduces a second radiation with a second polarization which is orthogonal to the first polarization. Individual transmitting amplifiers, in the case of a transmitting array, or individual receiving amplifiers (16A), in the case of a receiving array, are connected to the ports of each of the radiators. The amplifiers associated with the first ports of the respective radiators are connected, in turn, to phase shifters (18A) and attenuators (20A) which constitute a first beamformer for forming a set of one or more beams of radiation. The amplifiers (16A) associated with the second ports of the respective radiators are connected, in turn, to phase shifters (18A) and attenuators (20A) which constitute a second beamformer for forming a set of one or more beams of radiation. The two beamformers operate independently of each other so as to permit separately weighted polarization signals of the antenna to be programmed electronically for various polarizations such as right and left circular polarization or horizontal and vertical polarization. Also, the separately polarized waves associated with the first ports and the second ports permit dual polarization frequency reuse transmission.

Phased array based radar system for vehicular collision avoidance

Abstract: A phased array based radar and vehicular safety warning system for collision avoidance, including a phased array based radar, a controlling processor, and a warning system that also provides a warning to the driver of the equipped vehicle as well as drivers of other, non-equipped automobiles involved in an unsafe driving condition. The phased array radar includes a flexible antenna array that may be mounted conformally on existing automobiles without detracting from their design curvature. In one embodiment a pair of phased array radar antenna may be oriented towards opposing sides of an equipped automobile to provide warning surveillance of vehicles laterally approaching the equipped auto from the sides. In another embodiment a phased array radar antenna is oriented to the rear of the equipped automobile to provide warning surveillance of vehicles following the equipped auto too closely, and for warning of unsafe lane changes. In still another alternative embodiment a pair of phased array radar antenna having 180° fields of view may be installed in a pod mounted on the roof of the equipped automobile to provide 360° warning surveillance coverage.

Infinite phased arrays of cavity-backed patches

Abstract: An analysis of the radiation properties of infinite phased arrays of probe-fed circular microstrip patches backed by circular cavities using a rigorous Green's function/Galerkin's method is presented. The effect of substrate thickness on both scan volume and bandwidth performance is considered. Results are compared to those of infinite arrays of conventional probe-fed circular patch antennas. >

Multi-frequency band phased-array antenna using multiple layered dipole arrays

Abstract: A multiple layer dipole array that provides for a multi-frequency band phased array antenna. Several layers of dipole pair arrays, each tuned to a different frequency band, are stacked relative to each other along the transmission/reception direction. The highest frequency array is in front of the next lowest frequency array and so forth. Due to the frequency selective property of the arrays, incident high frequency signals are completely absorbed by the highest frequency array. In regard to incident low frequency signals, the insertion loss due to higher frequency arrays is small resulting in good performance of the lower frequency arrays. The multi-frequency band phased array antenna may use active or driven dipole pairs, or parasitic elements that form the multiple layer dipoles. The multiple layer dipole array of the present invention may employ corporate feed circuit boards and a corporate feed power divider, using strip transmission line circuits, for example. The multiple layer dipole phased array of the present invention may also employ a feed-through lens arrangement to simplify the feed network.

Spacecraft antennas and beam steering methods for satellite communciation system

Abstract: An advanced active element phased array satellite antenna is disclosed. Incorporating these novel antenna systems on a constellation of low Earth orbit spacecraft, allows phone customers worldwide to communicate through a system whose switching intelligence resides on orbit, bypassing traditional land-based networks, and offering a revolutionary expansion of communications potential. The present invention utilizes electronic beam steering is utilized to provide extremely high gain signals. In one preferred embodiment, a satellite (S) includes an Earth-facing array (10) of hexagonal antenna facets (12), mated together along their sides to form a slightly flattened, hemispherical shell. The antenna array (10) is connected to two rectilinear, unfurled, solar panels (P). The antennas (10) transmit and receive signals from terrestrial units located within the footprints (14) of the beams (11). Another embodiment (34) uses deployable, folding panels (41) which maximize panel surface area for a given weight and launch vehicle container volume. The panels (41) are stacked upon a central plate (39) along the depth axis of the container in accordion fold layers and are separately deployed radially from the center (C) of the central plate (39). The contour of the deployed panels permit the antenna beam footprints (14) to cover the desired area.

Liquid crystal-based optical time delay units for phased array antennas

Abstract: Novel two-dimensional (2-D) spatial light modulator (SLM)-based optical time delay units (OTDU's) using freespace/solid optics and fiber delays are introduced for phased array antenna and wideband signal processing applications. In particular, the mature nematic liquid crystal (NLC) SLM technology is considered for the proposed architectures. A 1/spl times/2 optical switch is demonstrated using a parallel-rub birefringent-mode NLC cell, a bulk optics cube polarizing beamsplitter, and a sheet polarizer. Switch measurements taken at 633 nm show a >3400:1 or >35 dB output port optical isolation. The 1/spl times/2 NLC switch is used to build a 1-bit, 3.33-ns-duration, free-space OTDU using mirrors and total internal reflection corner prisms. The unit demonstrated a >30 dB optical (or >60 dB electrical) signal-to-noise ratio for both delay and no-delay positions. A 1500 pixel NLC SLM is built, and a 128:1 or 21 dB on/off isolation is demonstrated limited by the digital drive electronics of thin-film transistor (TFT)-based pixel control. >

Ultrasound imaging system using line splicing and parallel receive beam formation

Abstract: In a phased array ultrasound imaging system, a high quality image is obtained by a combination of line splicing and parallel receive beamforming. Two transmit pulses, one focused in the near field and one focused in the far field, are transmitted sequentially at each steering angle. The transmitted ultrasound energy is preferably focused both in azimuth and in elevation. Ultrasound echos are simultaneously received along two receive scan lines spaced angularly on opposite sides of each transmit scan line. Signals received in response to the near field and far field transmit pulses are spliced together to provide signals that represent a high quality image throughout the region of interest. Image artifacts are reduced by blending the received signals near the splice between the near field and the far field, by dynamically steering the receive scan lines to reduce the effect of line warping, and by weighted averaging of adjacent scan lines.

Dynamic focusing in ultrasound hyperthermia treatments using implantable hydrophone arrays

Abstract: A prototype 16-element needle hydrophone array has been designed, fabricated and characterized. The primary use of this array is to provide acoustic feedback during ultrasound hyperthermia treatments. This feedback can be used to compensate for patient motion and tissue inhomogeneities by controlling the phased array driving patterns. It can also be used in adaptive dynamic focusing, a procedure which enables the phased array to focus at points away from specified control points. The hydrophone array consists of a PVDF sheet, which covers a silicon substrate carrier that contains the signal electrodes of the individual acoustic sensors. A complete description of the hydrophone array and its characteristics is given in this paper. The aberration correction and motion compensation algorithms are also described, and some experimental results are shown. Finally, a Taylor series based adaptive dynamic focusing method for phased arrays based on a set of discrete hydrophone array measurements is described. This algorithm does not require any prior knowledge of the applicator geometry and all the parameters needed for correction can be measured directly at the hydrophone array sensor locations. >

Design and experimental evaluation of an intracavitary ultrasound phased array system for hyperthermia

Abstract: For evaluating the feasibility of treating prostate cancer, a 64-element linear ultrasound phased array applicator for intracavitary hyperthermia was designed and constructed. A 64-channel ultrasound driving system including amplifiers, phase shifters, and RF power meters was also developed to drive the array. The design of the array and driving equipment are presented, as are the results of acoustical field measurements and in vitro perfused phantom studies performed with the array. Several techniques for heating realistically sized tumor volumes were also investigated, including single focus scanning and two techniques for producing multiple stationary foci. The results show that the operation of the array correlated closely with the theoretical model. When producing a single stationary focus, the array was able to increase tissue temperature by 12/spl deg/C in vitro in perfused phantom. With some minor improvements in array design, intracavitary phased arrays could be evaluated in a clinical environment. >

FD-TD analysis of Vivaldi flared horn antennas and arrays

Abstract: This paper summarizes a detailed computational study of Vivaldi flared horn antenna designs including single element, double element crossed-pair subarray elements, and linear arrays using the finite-difference time-domain (FD-TD) method. FD-TD, which numerically solves Maxwell's time dependent curl equations, accounts for the complex geometrical and electrical characteristics associated with this antenna design and array implementation. Validations have been made relative to a moment method (MM) model of an electrically large linearly tapered slot antenna. Also, good correlation is shown to exist in the primary features of the antenna patterns between computed and measured data for all cases. This work has achieved a number firsts for the FD-TD methodology. It represents the first "exact" computational model of a single quad Vivaldi slot antenna; the first "exact" computational model of a phased array of Vivaldi quad elements; and the first FD-TD model to demonstrate grating lobes for a phased array antenna of any sort. Lastly, this research represents an extensive study of the largest grid-based antenna models conducted to date. >

Experimental demonstration of an optical phased array antenna for laser space communications

Abstract: The feasibility of an optical phased array antenna applicable for spaceborne laser communications was experimentally demonstrated. Heterodyne optical phase-locked loops provide for a defined phase relationship between the collimated output beams of three single-mode fibers. In the far field the beams interfere with a measured efficiency of 99%. The main lobe of the interference pattern can be moved by phase shifting the subaperture output beams. The setup permitted agile beam steering within an angular range of 1 mr and a response time of 0.7 ms. We propose an operational optical phased array antenna fed by seven lasers, featuring high transmit power and redundance.

Dual band phased array antenna apparatus having compact hardware

Abstract: In a dual band array antenna apparatus having a plurality of first phased array antenna elements for a low frequency and a plurality of second phased array antenna elements for a high frequency, one transceiver module is provided for a number of the phased array first antenna elements, and microstrip lines of the first phased array antenna elements are changed to obtain a desired phase distribution at the first phased array antenna elements Also, one transceiver module is provided for each of the second phased array antenna elements

Ultra wideband phased array antenna.

Abstract: An ultra wideband (UWB) phased array antenna using a frequency-multiplexing, space-fed lens with a UWB feed horn achieves multi-octave bandwidth. The lens includes two UWB radiating apertures with relatively narrow band phase shifters connecting corresponding radiating elements of the arrays. Each aperture multiplexes the incoming UWB signal into separate frequency bands so that the phase shifters need only be tuned to these narrower frequency bands, and are set to form a beam in the desired direction. For wide instantaneous bandwidth operation, the beams from the various frequency bands are collimated in the same direction. For multi-mode operation, the beams corresponding to the various frequency bands are formed in different directions. The phase shifters need have a maximum phase shift of 360 degrees.

Development and field demonstration of a hardware-compressive fiber-optic true-time-delay steering system for phased-array antennas

Abstract: We describe the design, fabrication, testing, and antenna-range demonstration of a photonic wavelength-multiplexed true-time-delay steering system for use with broadband phased-array antennas. The prototype system is based on a unique hardware-compressive architecture and can drive 16 antenna elements over the 0.35–2.1-GHz band with 6-bit angular resolution over a ±45° scan angle.

Phased array radar antenna with two-stage time delay units

Abstract: A phased array antenna having two stages of time steering control that achieve system performance requirements at minimum cost. The first-stage which is traditionally located at the subarray level, is a multi-bit time delay unit that has a sufficient number of bits to meet the system's range resolution requirements. The second-stage located at the radiating element level, is a single-bit time delay unit that meets the system's two-way instantaneous bandwidth requirements. This combination of first-stage and second-stage time steering control minimizes the number of subarrays required to achieve the system performance requirements.

Floquet-based FDTD analysis of two-dimensional phased array antennas

Abstract: The finite-difference time-domain method with Floquet boundary conditions has been used to calculate the radiation characteristics of one- and two-dimensional phased array antennas for different scan angles in E- and H-planes. Considerable savings in computer memory and computation time are realized since only the central 3 elements for a l-D array and 3/spl times/3 elements for a 2-D array are to be modeled. >

Phased arrays of probe-fed stacked microstrip patches

Abstract: This paper presents calculated and measured results for infinite phased arrays of probe-fed stacked rectangular and circular microstrip patches. A numerical model is described that is based on a rigorous Green's function/Galerkin solution. In this solution, the connection of one or more vertical probe feeds to each patch is accurately modeled using a special attachment mode basis function, which is derived from the corresponding cavity model solution. Numerical results for both linearly and circularly polarized arrays are obtained. Measured results from a waveguide simulator are also presented and used to validate the numerical model. >

Synthesis of antenna patterns with imposed near-field nulls

Abstract: A pattern synthesis method, which incorporates deterministic nulls in the radiative near-field of an array is presented. The problem is formulated as a constrained least-mean-square approximation and an exact solution is given. Both linear and planar arrays are considered.