Showing papers in "IEEE Transactions on Aerospace and Electronic Systems in 1981"
TL;DR: In this paper, the observability requirements for bearings-only target motion analysis (TMA) were rigorously established by solving a third-order nonlinear differential equation, and closed form expressions were developed and subsequently used to specify necessary and sufficient conditions on own-ship motion that insure a uniquetracking solution.
Abstract: The observability requirements for bearings-only target motion analysis (TMA) are rigorously established by solving a third-order nonlinear differential equation. Closed form expressions are developed and subsequently used to specify necessary and sufficient conditions on own-ship motion that insure a uniquetracking solution. It is shown that for certain types of maneuvers the estimation process remains unobservable, even when the associated bearing rate is nonzero. Such maneuvers are frequently overlooked in heuristic discussions of TMA observability, which may account for some common misconceptions regarding the characteristics of acceptable own-ship motion.
377 citations
TL;DR: A method is presented for correcting the gain and phase imbalances and the bias errors of the in-phase and quadrature channels of a coherent signal processor by means of coefficients which are derived from measurements of a test signal.
Abstract: A method is presented for correcting the gain and phase imbalances and the bias errors of the in-phase and quadrature channels of a coherent signal processor [1] by means of coefficients which are derived from measurements of a test signal. The residual errors after correction depend upon the signal-to-noise ratio (S/N) of the test signal and the degree of filtering used in deriving the correction coefficients.
175 citations
TL;DR: In this article, a vertically scanned-beam synthetic aperture system (SCANSAR) is proposed as a solution to the ambiguity limitation of spaceborne synthetic aperture radar systems, where the potential length of synthetic aperture must be shared between beam positions, so the along track resolution is poorer; a direct tradeoff exists between resolution and swath width.
Abstract: Spaceborne synthetic aperture radar systems are severely constrained to a narrow swath by ambiguity limitations. Here a vertically scanned-beam synthetic aperture system (SCANSAR) is proposed as a solution to this problem. The potential length of synthetic aperture must be shared between beam positions, so the along-track resolution is poorer; a direct tradeoff exists between resolution and swath width. The length of the real aperture is independently traded against the number of scanning positions. Design curves and equations are presented for spaceborne SCANSARs for altitudes between 400 and 1400 km and inner angles of incidence between 20° and 40°. When the real antenna is approximately square, it may also be used for a microwave radiometer. The combined radiometer and synthetic-aperture (RADISAR) should be useful for those applications where the poorer resolution of the radiometer is useful for some purposes, but the finer resolution of the radar is needed for others.
166 citations
TL;DR: In this article, a comprehensive theory of interferometry from a system viewpoint with particular emphasis on the ambiguity resolution problem is developed, and a concept of acceptance criterion designed to reduce processing of erroneous measurements is developed.
Abstract: A comprehensive theory of interferometry from a system viewpoint with particular emphasis on the ambiguity resolution problem is developed. The derived error equations include contributions from all system uncertainties, i.e., phase measurement, frequency, and element phase center position errors in three dimensions. The direction-of-arrival errors are inversely proportional to the interferometer baseline and it is customary to make the baseline large enough to meet the accuracy requirements. A system with a baseline greater than a half-wavelength results in the well known direction-of-arrival ambiguity problem with the addition of a third element to each baseline being a common method for resolving the ambiguity. It is shown that contrary to previous thinking there are many equally optimal positions for adding the third element to resolve the ambiguity. In addition, it is shown how the measurement made to resolve the ambiguity can also be applied to increase the accuracy of the angle-of-arrival measurement. A central result is the derivation of expressions specifying the probability of correct resolution of ambiguities as a function of system parameters and system errors. Moreover the concept of an acceptance criterion designed to reduce processing of erroneous measurements is developed. Narrowing the criterion reduces the percentage of data accepted for processing, but increases the probability of correct ambiguity resolution. This is analogous to the relationship between the probability of detection and the probability of false alarm in radar theory.
129 citations
TL;DR: It is shown that bandlimiting the new codes prior to pulse compression acts as a waveform amplitude weighting which has the effect of increasing the mainlobe to sidelobe ratios.
Abstract: A new class of symmetric radar pulse compression polyphase codes is introduced which is compatible with digital signal processing. These codes share many of the useful properties of the Frank polyphase code. In contrast with the Frank code, the new codes are not subject to mainlobe to sidelobe ratio degradation caused by bandlimiting prior to sampling and digital pulse compression. It is shown that bandlimiting the new codes prior to pulse compression acts as a waveform amplitude weighting which has the effect of increasing the mainlobe to sidelobe ratios.
126 citations
TL;DR: The size and position of spurious peaks in the autocorrelation functions are discussed and the results are extended to narrowband ambiguity functions.
Abstract: Time-frequency hop codes are developed based upon the theory of linear congruences. These codes can be used for multiuser radar and asynchronous spread spectrum communications systems. A uniform upper bound is placed on the cross-correlation function between any two elements of the code set. The upper bound is minimized by choice of time-bandwidth product and is shown to diminish as 2/N, where N is the number of elements in the code set. The size and position of spurious peaks in the autocorrelation functions are discussed. The results are extended to narrowband ambiguity functions.
123 citations
TL;DR: In this paper, an interactive filter system is developed that provides an improved estimate of target motion states by conditioning kinematic filter estimates on target aspect angle data, and a novel statistical model for aircraft target normal acceleration is also developed to represent better the unknown target acceleration.
Abstract: A new approach to estimating motion of a highly maneuverable aircraft target in an air-to-air tracking scenario is presented. An interactive filter system is developed that provides an improved estimate of target motion states by conditioning kinematic filter estimates on target aspect angle data. Pattern recognition techniques used with an electrooptical tracker are presumed to provide this target aspect information. A target orientation filter processes the aspect angle measurements by statistically weighting measured aspect angles with the current best estimate of target kinematics. The aerodynamic lift equation is used to relate approximate angle of attack to target velocity and acceleration. A novel statistical model for aircraft target normal acceleration is also developed to represent better the unknown target accelerations. Simulation results of realistic three-dimensional scenarios are presented to evaluate the performance of the interactive filter system.
119 citations
TL;DR: In this article, closed-form steady-state equations are derived for the half-bridge series resonant converter with a rectified (dc) load, and normalized curves for various currents and voltages are then plotted as a function of the circuit parameters.
Abstract: Closed-form steady-state equations are derived for the halfbridge series resonant converter with a rectified (dc) load. Normalized curves for various currents and voltages are then plotted as a function of the circuit parameters. Experimental results based on a 10-kHz converter are presented for comparison with the calculations.
96 citations
TL;DR: A closed-form steady-state solution is presented for a three-state tracking filter with continuous position measurements and exponentially correlated target acceleration.
Abstract: A closed-form steady-state solution is presented for a three-state tracking filter with continuous position measurements and exponentially correlated target acceleration. Some other related closed-form solutions are discussed, and some comparative performance data is presented for the discrete measurement case.
85 citations
TL;DR: The application of importance sampling to the efficient simulation of low-probability events is discussed and a procedure is given for handling the case of multiple inputs where each is from a different statistical process.
Abstract: The application of importance sampling to the efficient simulation of low-probability events is discussed. Several examples are given to illustrate how the technique works for processes involving single and multiple statistical inputs. A procedure is also given for handling the case of multiple inputs where each is from a different statistical process.
78 citations
TL;DR: A new current injected equivalent circuit approach (CIECA) to modeling switching dc-dc converter power stages is developed, which results in either a set of equations which completely describe input and out-put properties or an equivalent linear circuit model valid at small signal, low frequency levels.
Abstract: A new current injected equivalent circuit approach (CIECA) to modeling switching dc-dc converter power stages is developed, which starts with the current injected approach and results in either a set of equations which completely describe input and out-put properties or an equivalent linear circuit model valid at small signal, low frequency levels. This approach to modeling switching dc-dc converter power stages has the merits but not the demerits of both the electronic equivalent circuit state space average approach and the current injected control type approach, namely, 1) the modeling is very clear and is simple whether the converter operates in continuous or discontinuous inductor conduction modes, 2) the modeling results in an equivalent circuit which is very close to the actual converter, and 3) the equivalent circuit can be used directly in the computer for theoretical predictions like SPICE, etc.
TL;DR: In this paper, the authors investigated the tradeoffs between volume removal, number of component signals, and the time-bandwidth product, and concluded that the signals must be frequency hop pulse trains.
Abstract: High-efficiency multicomponent signals for maximization of signalto-noise ratio are investigated. Maximization of signal-to-noise ratio in colored noise requires control of volume distribution of the signal ambiguity function and transmission of unity efficiency signals. Signal efficiency is defined as the ratio of average power to the peak power. It is concluded that the signals must be frequency hop pulse trains. Quadratic congruences are chosen to place the components in time-frequency space. The number-theoretic properties of these signals provide bounds on the position and amplitude of the various peaks of the signal ambiguity function. The tradeoffs are shown between volume removal, number of component signals, and the time-bandwidth product.
TL;DR: Two popular algorithms for nonlinearly constrained optimization are utilized to design the power converter: the sequential unconstrained minimization technique, SUMT Version 4; and the ALAG penalty function technique, ALAG5.
Abstract: A practical optimization approach for power converters is established which allows conception of a design to meet all powercircuit performance requirements and concurrently to optimize a defined quantity such as weight or losses. In addition to facilitating a cost effective design, the computer-aided approach provides a means to readily assess a) the weight-efficiency tradeoff, b) impacts of converter requirements and component characteristics on a given design, and c) optimum power-system configurations. The following two popular algorithms for nonlinearly constrained optimization are utilized to design the power converter: 1) the sequential unconstrained minimization technique, SUMT Version 4; 2) the ALAG penalty function technique, ALAG5. These algorithms are compared, and suggestions are made for improving the efficiency of the optimization algorithms for power converter design.
TL;DR: Weibull-distributed ground clutter of cultivated land was measured using an L-band long-range air-route surveillance radar (ARSR) having a 3.0?s pulsewidth and a 1.23° beamwidth at very low grazing angles between 0.21° and 0.32° as discussed by the authors.
Abstract: Weibull-distributed ground clutter of cultivated land was measured using an L-band long-range air-route surveillance radar (ARSR) having a 3.0 ?s pulsewidth and a 1.23° beamwidth at very low grazing angles between 0.21° and 0.32°. It is shown that the shape parameter of the Weibull distribution varied from c = 1.507 to c = 2.0, corresponding to the Rayleigh distribution.
TL;DR: In this paper, a simple extended Kalman filter was designed to track targets using outputs from a forward-looking infrared (FLIR) sensor as measurements, which exploits knowledge unused by current correlation trackers to yield enhanced performance.
Abstract: A simple extended Kalman filter has been designed to track targets using outputs from a forward-looking infrared (FLIR) sensor as measurements. It exploits knowledge unused by current correlation trackers ? size, shape, and motion characteristics of target, and atmospheric jitter spectral description ? to yield enhanced performance. In order to track air-to-air missiles at close range, it incorportateson-line adaptation to target shape effects, changing target motion characteristics, and maximum signal intensity. It is shown to possess considerable performance potential for highly maneuverable targets despite background clutter.
TL;DR: A technique is discussed for the design of multiple access frequency hopping patterns which will allow a number of users to communicate reliably over a limited bandwidth in the presence of Doppler and timing asynchronies.
Abstract: A technique is discussed for the design of multiple access frequency hopping patterns which will allow a number of users to communicate reliably over a limited bandwidth in the presence of Doppler and timing asynchronies. The patterns are based on a subset of the Reed-Solomon codewords. They possess nearly flat ambiguity and cross-ambiguity functions and thus could be useful as discrete radar signals. In addition the structure of the patterns permits a straightforward Implementation.
TL;DR: In this paper, the feasibility of using the indicated quadrature angle of arrival of a monopulse radar to discriminate a single target from multiple targets, separated in angle within a radar resolution cell, is investigated.
Abstract: The feasibility of using the indicated quadrature angle of arrival of a monopulse radar to discriminate a single target from multiple targets, separated in angle within a radar resolution cell, is investigated. The analysis is performed for steady (fixed) and Rayleigh fluctuating targets which cover a broad range of target characteristics. In both cases, the interfering signals due to noise and clutter in the sum and difference monopulse channels are assumed to be independent, zero-mean Gaussian processes. Detection and false alarm probabilities are evaluated analytically and the receiver operating characteristics are obtained for both fixed and fluctuating target cases. It is shown that multiple targets can be discriminated from a single target condition by integrating the indicated monopulse quadrature angle of arrival from several independent pulses. It is also shown that the probability of detecting multiple targets increases as the fluctuation in the target radar cross section decreases, approaching the fixed amplitude case in the limit.
TL;DR: In this article, the maximum likelihood estimates of the elevation angles of two closely spaced targets within the beamwidth were considered for an array divided into three subapertures, and a simple closed form solution was found whose accuracy compares favorably to the conventional maximum likelihood estimate which uses all the individual elements.
Abstract: The maximum likelihood estimates of the elevation angles of two closely spaced targets within the beamwidth is considered. For an array divided into three subapertures, a simple, closed form solution is found whose accuracy compares favorably to the maximum likelihood estimate which uses all the individual elements. Simulation results are presented for the case of a radar target located over a smooth reflecting surface.
TL;DR: In this article, concatenated sequences are suggested and developed for use in spread spectrum (SS) systems, and it has been shown that a processing gain of 60 is obtainable with a 15 × 4 concatenation sequence which requires three tapped delay lines (TDL), two of length 15 and one of 4.
Abstract: Concatenated sequences are suggested and developed for use in spread spectrum (SS) systems. Special receiver realization is discussed and it is shown that the concatenated sequences offer great advantage in reducing the size of the matched filter correlators (MFC) in the SS receiver. Experimental systems have been built using concatenated sequences and their performance is reported here. It has been shown that a processing gain of 60 is obtainable with a 15 × 4 concatenated sequence which requires three tapped delay lines (TDL), two of length 15 and one of 4. Thus a total of only 34 delay units (with a nonlinear interface network, only 19 delay units) are required. Teleprinter signals can be transmitted over telephone channels using a bandwidth (BW) expansion of 60 with an input signal-to-noise ratio (SNR) of only -5.1 dB, resulting in a character- error-rate of 1 in 103. Techniques have been developed to reduce the sidelobe levels in the aperiodic autocorrelation functions (ACF) of the pseudonoise (PN) codes. For 15 length and 7 length PN sequences, sidelobes are reduced by 9 dB and 9.4 dB, respectively, using transversal filters. Application of the SS systems to the problem of multiaccessing and antijamming are discussed.
TL;DR: In this paper, the tracking accuracies for the radial component of motion are computed for a track-while-scan radar system which obtains position and rate data during the dwell time on a target.
Abstract: Tracking accuracies for the radial component of motion are computed for a track-while-scan radar system which obtains position and rate data during the dwell time on a target These results will be of interest to persons developing trackers for pulse Doppler surveillance radars. The normalized accuracies, computed for a two state Kalman tracking filter with white noise maneuver capability, are shown to depend upon two parameters, r = 4?0/?aT2 and s = ?dT/?0. The symbols ?0 and ?d are the position and rate measurement accuracies, respectively, ?a is the standard deviation of the white noise maneuver process and T is the antenna scan time. The scalar tracking filter equations are derived and numerical results are presented. Lower steady state tracking errors plus the earlier attainment of steady state accuracies are the direct consequence of incorporating the rate measurements into the tracking filter.
TL;DR: In this article, the selection of the optimum features for aircraft classification from radar returns was studied, and a constraint was imposed that a minimum number of simultaneous frequencies be used for classification.
Abstract: The selection of the optimum features for aircraft classification from radar returns was studied. A constraint was imposed that a minimum number of simultaneous frequencies be used. The results indicate that a high reliability of classification is achievable with only two frequencies, and even a single frequency can provide over 95 percent reliability if both phase and amplitude at two orthogonal polarizations are used. The data set tested involved eight military aircraft whose sizes varied over a three-to-one range.
TL;DR: It is found that a filter based on the technique of statistical linearization performs better than the extended Kalman in this application, believed to be the first application of the statistically linearized filter to a practical dynamics problem.
Abstract: Several filters are applied to the problem of state estimation from inertial measurements of reentry drag. This is a highly nonlinear problem of practical significance. It is found that a filter based on the technique of statistical linearization performs better than the extended Kalman in this application. This is believed to be the first application of the statistically linearized filter to a practical dynamics problem. A sensitivity analysis is performed to demonstrate the relative insensitivity of this filter to modeling errors and approximations.
TL;DR: In this article, it was shown that the ambiguity volume is asymptotically conserved as the signal approaches the narrowband case, which is a lower bound for the volume of the wideband ambiguity function.
Abstract: It is shown that the volume under the wideband ambiguity function is close to the square of the signal energy. The ambiguity volume is asymptotically conserved as the signal approaches the narrowband case. The narrowband ambiguity volume is a lower bound for the volume of the wideband ambiguity function.
TL;DR: In this article, the development of a solar pressure control system for three-axis attitude control of Earth-oriented spacecraft is presented, and a controller configuration consisting of two rotatable mirror-like surfaces, representing the minimum hardware implementation, is considered.
Abstract: The development of a solar pressure control system for three-axis attitude control of Earth-oriented spacecraft is presented. A controller configuration consisting of two rotatable mirrorlike surfaces, representing the minimum hardware implementation, is considered. Optimal control theory is applied to synthesize a feedback control law directly governing the differential rotation of the control surfaces. The system performance is evaluated through the response analysis of a satellite subject to destabilizing gravity gradient torques as well as external disturbances. Even under such adverse conditions, the results indicate a moderately sized controller to be quite effective in maintaining the desired Earth-pointing spacecraft orientation. The validity of the optimal control law is established for all times of the year, and the feasibility of implementing suboptimal control policies is also examined.
TL;DR: In this paper, the bit error probability for coherent phase-shift keying (CPSK) signaling was evaluated in the presence of Gaussian atmospheric noise and signal fading in a more reasonable representation of the communication channel.
Abstract: Recently the performance of digital communication systems in the presence of impulsive atmospheric noise has been evaluated assuming a noise model which is in excellent agreement with experimental results. We evaluate the bit error probability for coherent phase-shift keying (CPSK) signaling assuming the same atmospheric noise model but considering a more reasonable representation of the communication channel which accounts for the simultaneous presence of Gaussian (always present) atmospheric noise and signal fading.
TL;DR: The maximum likelihood method (with unresolved detections) does not appear to be implementable in real time without very high speed integrated circuit (VHSIC) technology, but it can be used as a standard to which more implementable methods can be compared.
Abstract: In a dense detection environment track-while-scan algorithms will introduce many false tracks when processing is performed on a scan-by-scan basis. The maximum likelihood solution involving all detections on all scans is formulated and evaluated for the initiation problem consisting of false alarms, missed detections, and unresolved detections. A comparison is made between the maximum likelihood solutions including and not including the resolution likelihood and it is shown that the resolution likelihood must be included if the data contain unresolved detections. While the maximum likelihood method (with unresolved detections) does not appear to be implementable in real time without very high speed integrated circuit (VHSIC) technology, it can be used as a standard to which more implementable methods can be compared.
TL;DR: A monopulse receiver exhibits three apparently distinct types of average response when the radar sees two jammers, two passive targets, or one of each; this variety of response types is analyzed and shown to be consistent.
Abstract: A monopulse receiver exhibits three apparently distinct types of average response when the radar sees two jammers, two passive targets, or one of each. This variety of response types is analyzed and shown to be consistent, i.e., the responses are shown to be special cases of a general formula which applies to two independent targets with uniformly distributed phase difference.
TL;DR: In this article, the nonlinear system concepts of nonlinear transfer functions are extended to nonlinear cross sections which may be used to quantitatively describe the characteristics of a nonlinear scatter.
Abstract: The nonlinear system concepts of nonlinear transfer functions are extended to nonlinear cross sections which may be used to quantitatively describe the characteristics of a nonlinear scatter. The concept of nonlinear cross sections is used to generalize the radar equation for nonlinear scattering objects.
TL;DR: In this article, a procedure is demonstrated for fitting gravity disturbance correlation functions with finite-dimensional state-space models, which is needed to design the Kalman filters used for gradiometer-aided inertial navigation.
Abstract: State-space models of gravity disturbance gradients are needed to design the Kalman filters used for gradiometer-aided inertial navigation. However, the physics of the gravity field guarantee that many of the cross-spectral densities of gravity disturbance gradients are nonrational. A procedure is demonstrated for fitting gravity disturbance correlation functions with finite-dimensional state-space models.
TL;DR: An effective relay management solution applicable to multiple terminal ground- to-ground or ground-to-air line-of-sight communication environments is described and computer simulation results show how a static or dynamically changing user geometry can be managed.
Abstract: An effective relay management solution applicable to multiple terminal ground-to-ground or ground-to-air line-of-sight communication environments is described. Algorithms are developed which enable terminals first to recognize the existence or availability of other terminals, and second, to self-organize a community of terminals rapidly into local nets without the need for a master control terminal. Computer simulation results show how a static or dynamically changing user geometry can be managed. Network connectivity is provided automatically and the system protects itself against the loss of a master user by not requiring one.