Showing papers in "IEEE Transactions on Aerospace and Electronic Systems in 1980"
TL;DR: In this paper, an aircraft is imaged from both a straight flight and a turn with recognizable results, showing that two phases exist in the radar return, one being gross velocity induced, the other being interscatterer interference within the target itself.
Abstract: Imaging from ground-based (stationary) radars of moving targets is often possible by utilizing a "synthetic aperture" developed from the target motion itself. The theory and experimental results associated with such processing are addressed. An aircraft is imaged from both a straight flight and a turn with recognizable results. Analysis shows that two-phase components exist in the radar return, one being gross velocity induced, the other being interscatterer interference within the target itself. The former phase must be removed prior to imaging and techniques are developed for this task. Preprocessing, range curvature, range alignment, motion compensation, and presumming are all addressed prior to presenting the experimental results. Coherence processing intervals, range collapsing, and range realignment are all examined during the processing aspects of the paper.
752Â citations
TL;DR: In this article, the effects of various system aberrations are investigated and experimental results from a microwave test range which demonstrate the image improvement are presented, along with an analysis of the three-dimensional radar/object geometry with separate source and receiver locations.
Abstract: During the integration time required to obtain fine Dopplerfrequency resolution in a range-Doppler imaging radar, a point on a rotating object may move through several range and Doppler resolution cells and produce a smeared image. This motion can be compensated by storing the appropriately processed return pulse, and the angular coordinates are determined by the angular coordinates of the radar antenna. The resulting stored data represents the three-dimensional Fourier transform of the object reflectivity density, and hence can be processed by an inverse Fourier transformation. Also included is an analysis of the three-dimensional radar/object geometry with separate source and receiver locations. The effects of various system aberrations are investigated and experimental results from a microwave test range which demonstrate the image improvement are presented.
652Â citations
TL;DR: The effects of aliasing (including pseudoaliasing), picket-fence effect, and leakage in the fast Fourier transform (FFT) are presented.
Abstract: The effects of aliasing (including pseudoaliasing), picket-fence effect, and leakage in the fast Fourier transform (FFT) are presented. A computer program was written to perform the FFT analysis of known inputs. The program has the capability of detecting aliasing by calculating an "aliasing coefficient" (Q), and will increase the sampling frequency and the number of points in the input sequence if aliasing occurs. The term "pseudoaliasing" is a phenomenon which is similar to aliasing (or fold-over) but related to the effects of picket fence and leakage. The "leakage coefficient" (ri) is a quantitative measure of the deviation from the fundamental frequency component with respect to the sampling frequency, when the input sequence has only one frequency component.
265Â citations
TL;DR: Satellite constellations having rosette (flowerlike) orbital patterns are described which exhibit better worldwide coverage properties thanconstellations previously reported in U.S. literature and offer a promising alternative to the use of geostationary satellites.
Abstract: Satellite constellations having rosette (flowerlike) orbital patterns are described which exhibit better worldwide coverage properties than constellations previously reported in U.S. literature. The best rosettes with 5-15 satellites are identified and evaluated relative to prior results. In most cases, the best results are obtained by placing one satellite in each of N separate planes and by using inclined rather than polar orbits. Coverage properties of these constellations are analyzed in terms of the largest possible great circle range between an observer anywhere on the Earth's surface and the nearest subsatellite point. When evaluated in this manner, coverage properties are invariant with deployment altitude. As deployment altitude is reduced, however, higher order constellations must be used to maintain a fixed minimum viewing angle. Coverage properties are also invariant with deployment orientation relative to Earth coordinates, although specific orientations can cause the satellite patterns to appear quasi-stationary. Thus these constellations offer a promising alternative to the use of geostationary satellites. Rosette constellations can also be used to guarantee multiple satellite visibility on a continuous worldwide basis. It is shown that 5, 7, 9, and 11 satellites are the minimum numbers required for single, double, triple, and quadruple visibility, respectively. Examples of rosette constellations which achieve these bounds are given.
226Â citations
TL;DR: In this article, the authors present analytical results for a square law detector and a Swerling case 1 fluctuating target, supplemented by simulation results for non-fluctuating target and envelope and logarithmic detector laws.
Abstract: Curves are presented showing the additional constant false-alarm rate (CFAR) loss which results when a "greatest of" logic is imple mented between the leading and lagging sets of reference cells. Thee analytical results for a square law detector and a Swerling case 1 fluctuating target are supplemented by simulation results for a nonfluctuating target, and envelope and logarithmic detector laws.
211Â citations
TL;DR: It is shown that the number of independent vector measurements required for the matrix estimator can be decreased by up to a factor of two.
Abstract: The optimum weights for an adaptive processor are determined by solving a particular matrix equation. When, as is usually true in practice, the covariance matrix is unknown, a matrix estimator is required. Estimating the matrix can be computationally burden some. Methods of decreasing the computational burden by exploiting persymmetric symmetries are discussed. It is shown that the number of independent vector measurements required for the estimator can be decreased by up to a factor of two.
177Â citations
TL;DR: In this paper, it is shown that if the true signal direction is not known exactly or if the data containing the interference are corrupted by a desired signal, then more samples are required to ensure that the estimated weighting vector gives a near optimal performance.
Abstract: Digital control of adaptive arrays has been shown to be a feasible alternative to analog feedback-loop control. As the eigenvalue spread of the correlation matrix no longer controls the speed of adaption, one merely has to ensure that enough samples have been taken so that the matrix estimate is close to the true matrix. While previous studies have assumed ideal conditions, it is shown here that if the true signal direction is not known exactly or if the data containing the interference are corrupted by a desired signal, then more samples are required to ensure that the estimated weighting vector gives a near optimal performance.
112Â citations
TL;DR: In this article, a discrete time model for simulation of the dynamics of samarium cobalt-type permanent magnet brushless dc machines is presented, which includes modeling of the interaction between these machines and their attached power conditioners.
Abstract: A discrete time model for simulation of the dynamics of samarium cobalt-type permanent magnet brushless dc machines is presented. The similation model includes modeling of the interaction between these machines and their attached power conditioners. These are transistorized conditioner units. This model is part of an overall discrete-time analysis of the dynamic performance of electromechanical actuators, which was conducted as part of prototype development of such actuators studied and built for NASA-Johnson Space Center as a prospective alternative to hydraulic actuators presently used in shuttle orbiter applications. The resulting numerical simulations of the various machine and power conditioner current and voltage waveforms gave excellent correlation to the actual waveforms collected from actual hardware experimental testing. These results, numerical and experimental, are presented here for machine motoring, regeneration and dynamic braking modes. Application of the resulting model to the determination of machine current and torque profiles during closed-loop actuator operation were also analyzed and the results are given here. These results are given in light of an overall view of the actuator system components. The applicability of this method of analysis to design optimization and trouble-shooting in such prototype development is also discussed in light of the results at hand.
110Â citations
TL;DR: In this article, linear programming techniques were used to determine the optimal filter weights for minimizing the peak range sidelobes of a binary phase-coded waveform, and the resulting filter was compared with the filter obtained by use of the least square approximation to the ideal inverse filter.
Abstract: Linear programming techniques are utilized to determine the optimal filter weights for minimizing the peak range sidelobes of a binary phase-coded waveform. The resulting filter is compared with the filter obtained by use of the least square approximation to the ideal inverse filter. For a test case using the 13-element Barker code the linear programming filter is found to have peak sidelobes as much as 5 dB lower than the least squares filter of the same length.
108Â citations
TL;DR: In this paper, a procedure for the design of a pair of sensitivity discriminating Luenberger observers for instrument failure detection (IFD) is presented, which permits detection of instrument malfunctions with reduced sensitivity to process parameter variations.
Abstract: A procedure is presented for the design of a pair of sensitivity discriminating Luenberger observers for instrument failure detection (IFD). The proposed IFD scheme permits detection of instrument malfunctions with reduced sensitivity to process parameter variations. The efficiency of detecting instrument malfunctions and the influence of parameter variations are illustrated with an example.
92Â citations
TL;DR: In this article, the performance of a steered beam adaptive array as a function of the beam pointing error is examined, and it is shown that the beam point error that can be tolerated is essentially a question of dynamic range.
Abstract: The performance of a steered beam adaptive array as a function of the beam pointing error is examined. The purpose is to determine how close the steered beam has to be to the actual desired signal arrival angle for good performance. It is shown that the beam pointing error that can be tolerated is essentially a question of dynamic range. The greater the desired signal dynamic range that must be accommodated by the array, the more accurate the beam pointing angle must be.
TL;DR: In this paper, a new soft limiter model is proposed to change the knee sharpness while maintaining small signal linearity, and both instantaneous and bandpass limiter characteristics are discussed.
Abstract: Soft limiter models used in the past do not provide a convenient way of changing the knee sharpness while maintaining small signal linearity. A new model is described which does this. Both instantaneous characteristics and bandpass limiter characteristics are discussed. The model is also suitable for analyzing and simulating compressors, expanders, and detectors.
TL;DR: In this paper, the authors describe a special case where circular-projection radar data are coherently processed to yield both azimuth and range resoultion, using data obtained from the radar target scatter site (RAT SCAT) radar cross-section facility.
Abstract: In recent years synthetic-aperture radars (SAR) have proven to be very useful two-dimensional imaging tools in various fields. Based on the synthetic-aperture concepts, different imaging modes are possibe with various operating characteristics. We describe a special case where circular-projection radar data are coherently processed to yield both azimuth and range resoultion. Experiments are performed using data obtained from the radar target scatter site (RAT SCAT) radar cross-section facility. Fairly good results are obtained which illustrate the versatility of coherent syntheticaperture processing of pulse-to-pulse high-range-resolution radar returns. A discrete multifrequency stepped and pulsed waveform is the basic transmitted signal from which range-Doppler images are generated. The RAT SCAT turntable facility allows interesting model targets to be illuminated from which radar images can then be computed. One such application of the processing is described.
TL;DR: In this paper, the authors derived the location of the intercept point in target-centered coordinates (the counter-weapon aimpoint), analyzes the complicated behavior of range and bearing settings with attack geometry, and formulates the relations for determining whether any given attack can be countered under restrictions on speed or angle at which the counterweapon may be fired.
Abstract: Previous correspondence [1, 2] considered the problem of defending moving target by means of a counterweapon launched from the target to intercept the attacker, deriving relations between attacker-target ranges at counterweapon launch and at intercept of the attacker, and the speed capabilities of the counterweapon. The present correspondence derives the location of the intercept point in target-centered coordinates (the counterweapon aimpoint), analyzes the complicated behavior of range and bearing settings with attack geometry, and formulates the relations for determining whether any given attack can be countered under restrictions on speed or angle at which the counterweapon may be fired. Exhaustive analysis is not attempted. A simplified treatment portrays kinematic conditions which must exist if the target is to counter the attack before the target is impacted by the attacking vehicle, through the use of examples.
TL;DR: In this paper, a simplified version of the dedicated observer scheme is used to detect sensor faults in an operating automatic system by adding a random disturbance of moderate intensity, driven by a single sensor.
Abstract: Sensor faults are detected in an operating automatic system by a simplified version of the dedicated observer scheme Control inputs are augmented by a random disturbance of moderate intensity The dedicated observer in this case is a Kalman filter, driven by a single sensor This filter provides estimates of the outputs from the other, nonredundant, sensors A logical combination of these functionally redundant signals with the actual sensor signals provides prompt detection of incipient faults on all instruments without false alarms The scheme is applied to a simulation of the lateral axis control system of a hydrofoil boat in which four sensors are to be covered by the fault detection scheme Tests indicate that the scheme is robust with respect to variations in the intensity of the random disturbance
TL;DR: In this article, a continuously adaptive two-dimensional Kalman tracking filter for a low data rate track-while-scan (TWS) operation is introduced which enhances the tracking of maneuvering targets.
Abstract: A continuously adaptive two-dimensional Kalman tracking filter for a low data rate track-while-scan (TWS) operation is introduced which enhances the tracking of maneuvering targets. The track residuals in each coordinate, which are a measure of track quality, are sensed, normalized to unity variance, and then filtered in a single-pole filter. The magnitude Z of the output of this single-pole filter, when it exceeds a threshold Z1 is used to vary the maneuver noise spectral density q in the Kalman filter model in a continuous manner. This has the effect of increasing the tracking filter gains and containing the bias developed by the tracker due to the maneuvering target. The probability of maintaining track, with reasonably sized target gates, is thus increased, The operational characteristic of q versus Z assures that the tracker gains do not change unless there is high confidence that a maneuver is in progress.
TL;DR: A history of engineering education in the United States is described in this article, beginning with General Washington's general order in 1778 calling for the establishment of a school of engineering and concluding with a discussion of the general trends in engineering education today.
Abstract: A history of engineering education in the United States is described, beginning with General Washington's general order in 1778 calling for the establishment of a school of engineering and concluding with a discussion of the general trends in engineering education today. Emphasis is placed on the needs of a continually growing nation and on the ways in which engineering education has responded to these needs.
TL;DR: In this article, the authors presented data in normalized form, showing steady-state filtering and smoothing performance for optimum three-state estimators which assume exponentially correlated acceleration of the tracked object.
Abstract: Computed data is presented, in normalized form, showing steady-state filtering and smoothing performance for optimum three-state estimators which assume exponentially correlated acceleration of the tracked object. The data are useful for preliminary design, gain selection, and performance prediction.
TL;DR: In this paper, the authors attempt to approach the broad issues of IFFN (identification, friend, foe, neutral) of military targets via the techniques of NCTR (noncooperative target recognition), coupled with the systems approach called "sensor fusion".
Abstract: Fowler's Seventh Law for military systems [1] states: "Be wary of proposals for synergistic systems. Most of the time when you try to make 2 + 2 = 5, you end up with 3-and sometimes 1.9." We attempt to approach the broad issues of IFFN (identification, friend, foe, neutral) of military targets via the techniques of NCTR (noncooperative target recognition), coupled with the systems approach called "sensor fusion." Although the overall style of the paper is that of a tutorial, many of the results presented are original. In all cases where we make political obsrvations, they represent our personal opinions.
TL;DR: Phase shift for the ramp-comparator pulsewidth modulator between a continuous input control signal and the signal frequency component of the output is analyzed and it is shown that transport lag is not implicit to these PWM systems in general but rather depends upon the existence of explicit delays.
Abstract: Phase shift for the ramp-comparator pulsewidth modulator (PWM) between a continuous input control signal and the signal frequency component of the output is analyzed. It is shown that transport lag is not implicit to these PWM systems in general but rather depends upon the existence of explicit delays between the time at which a switching decision is made and the time at which that decision is executed.
TL;DR: An adaptive multibeam antenna, suitable for time-multiplexed, multichannel signals, is described here to permit successful communication and signal direction-of-arrival tracking in the presence of a large number of sidelobe interferers and a small number of main-beam interferers.
Abstract: Narrow-beam, low-sidelobe antennas may be used to enhance communication in the presence of sidelobe interferers. Protection against main-beam interferers as well can be obtained through the use of an adaptive multibeam antenna. Such an antenna, suitable for time-multiplexed, multichannel signals is described here. The objective is to permit successful communication and signal direction-of-arrival tracking in the presence of a large number of sidelobe interferers and a small number of main-beam interferers.
TL;DR: In this article, a converter topology is described that minimizes the task these components must perform and thereby achieves a significant improvement in power supply density, which can be used to reduce power consumption.
Abstract: Dramatic reductions in size and weight have been achieved in the area of signal and information processing. Power conditioning circuits have not kept pace, primarily due to the relatively slow proggress ress in the passive energy storage and transformation devices. A novel converter topology is described that minimizes the task these components must perform and thereby achieve a significant improvement in power supply density.
TL;DR: In this article, the steady state performance of the Frost power inversion array is evaluated, assuming constant rotational velocity of the external noise environment in the sin? domain, and approximate criteria are derived for weight vector and output power deviation from optimal values.
Abstract: The steady state performance of the Frost power inversion array is evaluated, assuming constant rotational velocity of the external noise environment in the sin ? domain. The weight vector is solved implicitly in terms of a linear matrix equation. Approximate criteria are derived for weight vector and output power deviation from optimal values, which are then applied to determine the maximum scan rate of a radar sidelobe canceler.
TL;DR: In this paper, an algebraic transformation method is used to reduce the order of the Riccati differential equation and to obtain explicit expressions for the filter gains (in terms of the interceptor /target separation range) which results in a substantial reduction of the computer burden involved in estimating the target states.
Abstract: The problem of solving the matrix Riccati differential equation in the design of Kalman filters for the target tracking problem is considered. An algebraic transformation method is used to reduce the order of the Riccati differential equation and to obtain explicit expressions for the filter gains (in terms of the interceptor /target separation range) which results in a substantial reduction of the computer burden involved in estimating the target states. The applicability of the transform technique is demonstrated for the receiver thermal noise and the target glint noise cases.
TL;DR: A modification to the adaptive array under the directional constraint is proposed to improve its performance of rejecting wideband interference by analogy to the pattern synthesis of an antenna array, an additional quantity that corresponds to the derivative of the pattern is generated and combined with the standard feedback quantity to control the weights of the array.
Abstract: A modification to the adaptive array under the directional constraint [1] is proposed to improve its performance of rejecting wideband interference. By analogy to the pattern synthesis of an antenna array which produces a flat null in its radiation pattern, an additional quantity that corresponds to the derivative of the pattern is generated and combined with the standard feedback quantity to control the weights of the array. This composite system is tested by computer simulation experiments and the following points are demonstrated in contrast to the conventional, simple system: 1) faster adaptation against wideband interference, 2) remarkable improvement of the signal-to-noise ratio of the output, i. e., very small fluctuation.
TL;DR: In this paper, the effect of a common-mode choke on the noise suppression is discussed experimentally, and the effects of parasitic parameters on noise voltage and frequencies are clarified by means of a high-frequency equivalent circuit.
Abstract: Analytical and experimental considerations of the common-mode noise in a dc-to-dc connverterare discussed. Analyzing the mechanism of the common-mode noise generation by means of a high-frequency equivalent circuit, we estimate the output noise voltage generated during the transistor's turn-on time. This commonmode noise consists mainly of two frequency components distributed in several megahertz. The effects of parasitic parameters on the noise voltage and frequencies are clarified. In addition, the effect of a common-mode choke on the noise suppression is discussed experimentally.
TL;DR: In this article, a new technique is described by which radar tracks can be established and maintained in a dense multitarget environment, where targets may fly in formation, maneuver relative to each other, or be on crossing paths.
Abstract: A new technique is described by which radar tracks can be established and maintained in a dense multitarget environment. These targets may fly in formation, maneuver relative to each other, or be on crossing paths. They may fade and reappear, lose their resolution, or become resolved. If the formation members move apart, the formation track is split into separate tracks. Typical requirements for a formation tracking system are stated, followed by a discussion of the principles on which this design is based. The same logic applies both to single targets and to forma. tions. Finally, results from field tests are presented.
TL;DR: Differential Doppler measurements by a passive array are used to track an unstable continuous wave (CW) source moving in a ballistic trajectory, e.g., a projectile carrying a proximity fuse as discussed by the authors.
Abstract: Differential Doppler measurements by a passive array are used to track an unstable continuous wave (CW) source moving in a ballistic trajectory, e.g., a projectile carrying a proximity fuse. The ballistic equations of motion couple frequency measurements at various sections along the track with the track parameters at any arbitrary time, e.g., at impact. A nonlinear weighted leastsquare method is used to estimate the track parameters, and the resulting error covariance matrix is derived. A numerical example demonstrates the relative contributions of various frequency measurements to the estimation accuracy.
TL;DR: In this paper, the authors present an improved form of an adaptive array feedback loop which has the property that its time constants are fixed, which is an advantage over the well-known least mean square (LMS) loop, for which time constants depend on received signal power.
Abstract: This paper is concerned with the problem of time constants in adaptive arrays. The paper presents a improved form of an adaptive array feedback loop, which has the property that its time constants are fixed. This property is an advantage over the well-known least mean square (LMS) loop, for which time constants depend on received signal power. Fixed time constants are of interest because they simplify dynamic range problems for adaptive arrays in communication and radar systems.
TL;DR: Explicit expressions of range, velocity, and the angle between them, as functions of a radar Doppler shift and its first two derivatives are given in this article, where they are expressed as
Abstract: Explicit expressions of range, velocity, and the angle between them, as functions of a radar Doppler shift and its first two derivatives are given.