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Aerospace and Electronic Systems, IEEE Transactions on

Issue 3 • Date July 1997

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Displaying Results 1 - 25 of 39
  • Doppler ambiguity resolution using multiple PRF

    Publication Year: 1997 , Page(s): 738 - 751
    Cited by:  Papers (13)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2082 KB)  

    An algorithm for velocity ambiguity resolution in coherent pulsed Doppler radar using multiple pulse repetition frequencies (PRF) is presented. It relies on the choice of particular values for the PRFs. The folded frequency of the target signal is obtained by averaging the folded frequency estimates for each PRF, and a quasi maximum likelihood criterion is maximized for ambiguity order estimation. The fast implementation of this nonambiguous estimation procedure is based on the fast Fourier transform (FFT), The proposed waveform allows full exploitation of any (even) number of PRFs, which appears to be important for estimation improvement. The effects of the waveform parameters and the folded frequency estimation variance on the performance of the ambiguity order estimation procedure are evaluated theoretically and through computer simulations. Mean square error (MSE) curves are given to assess the Doppler frequency estimation accuracy. Finally, the new method is compared with a classical technique and the implementation of the algorithm in a clutter environment is addressed. View full abstract»

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  • Fuzzy logic applications to multisensor-multitarget correlation

    Publication Year: 1997 , Page(s): 752 - 769
    Cited by:  Papers (22)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4376 KB)  

    A consistent tactical picture requires data fusion technology to combine and propagate information received from diverse objects and usually vague situations. The information may be contained in two types of data; numerical data received from sensor measurements, and linguistic data obtained from human operators and domain experts. In real world situations, the numerical data may be noisy, inconsistent, and incomplete, and the linguistic information is imprecise and vague. To deal with these two types of data simultaneously, fuzzy sets and fuzzy logic provide a methodology to obtain an approximate but consistent tactical picture in a timely manner for very complex or ill-defined engineering problems. A functional paradigm for fuzzy data fusion is presented. It consists of four basic elements: (1) fuzzification of crisp elements, (2) fuzzy knowledge base derived from numerical input/output relations and humans, (3) fuzzy inference mechanism based on a class of fuzzy logic, (4) defuzzification of fuzzy outputs into crisp outputs for use by a plant. For real-time practical systems, the on-line determination of a fuzzy membership function from a given set of crisp inputs is vital. To this end, a methodology for estimating an optimal membership function from crisp input data has been implemented. This is based on the possibility/probability consistency principle as proposed by L.A. Zadeh. A relationship between the fuzzy membership function and the confidence level of statistical input data has been developed and it serves as a design parameter for fuzzification. This technique has been applied to a two-dimensional multisensor-multitarget tracking system. Fuzzy system performance evaluations have been presented. With simulated data in the laboratory environment, the simulation has been performed to evaluate the Mission Avionics Sensor Synergism (MASS) Systems. These results show better performance for the data correlation function using the fuzzy logic techniques. View full abstract»

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  • Geolocation of a known altitude object from TDOA and FDOA measurements

    Publication Year: 1997 , Page(s): 770 - 783
    Cited by:  Papers (22)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1387 KB)  

    Most satellite systems for locating an object on Earth use only time difference of arrival (TDOA) measurements. When there are relative motions between an emitter and receivers, frequency difference of arrival (FDOA) measurements can be used as well. Often, the altitude of an object is known (it is zero, for example) or can be measured with an altimeter. Two sets of geolocation solutions are proposed which exploit the altitude constraint to improve the localization accuracy. One is for TDOAs alone and the other for the combination of TDOA and FDOA measurements. The additional complexity by imposing the constraint is a one-dimensional Newton's search and the rooting of a polynomial. The covariance matrices of the new estimators are derived under a small measurement noise assumption and shown to attain the constrained Cramer-Rao lower bound (CRLB). When there is a bias error in the assumed altitude, using the altitude constraint will introduce a bias to the solution. Since applying the constraint decreases the variance, there is a tradeoff between variance and bias in the mean square error (MSE). The maximum allowable altitude error such that the constraint solution will remain superior to the unconstraint is given. Simulation results are included to corroborate the theoretical development. View full abstract»

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  • Detection of chi-square fluctuating targets in arbitrary clutter

    Publication Year: 1997 , Page(s): 784 - 794
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1587 KB)  

    In a recent paper, general expressions were derived for the density and cumulative probability functions of the amplitude of a linear matched-filter output given a nonfluctuating target in a clutter-limited environment. These expressions were based on the clutter amplitude density function. The results are extended to calculate the cumulative probability function of the output of a linear matched filter used to detect a chi-square fluctuating target in a clutter-limited environment. The resulting method is applied to a common radar clutter model, and experimental sonar data. View full abstract»

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  • Extracting multiple frequencies from phase-only data

    Publication Year: 1997 , Page(s): 795 - 801
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1259 KB)  

    The problem of extracting multiple frequencies from phase-only data is addressed. Multiple frequency estimation is accomplished by reconstructing the Fourier transform of the complex-valued time signal and then finding peaks in the frequency domain. We present a set of conditions under which a discrete-time complex sequence can be completely specified by its phase-only information. Two candidate multiple frequency estimation schemes are introduced, one based on a closed-form least-squares inverse, the other an iterative reconstruction algorithm. The uniqueness of the closed-form solution and the convergence of the iterative scheme have been proven under certain conditions. Several examples are given, including the case where the phase is quantized as would happen in an analog-to-digital (A/D) converter. Extensions to the multidimensional case, and to the case of real-part only reconstruction are straightforward. View full abstract»

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  • Automatic stereo processing of high resolution radar imagery

    Publication Year: 1997 , Page(s): 802 - 812
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (7826 KB)  

    Previously reported experiments with stereoscopic viewing of high resolution radar pictures demonstrated improvements in detection sensitivity up to 7 dB. This paper presents continued research into automatic algorithmic techniques for employing stereo information. A simple two-stage model for a human observer is proposed, and here we investigate the utility of an existing automatic stereo processor technique in application to radar imagery. It is shown that results obtained with the automatic processor very closely resemble those obtained through actual stereo viewing of radar pictures. View full abstract»

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  • TMA from bearings and multipath time delays

    Publication Year: 1997 , Page(s): 813 - 824
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1368 KB)  

    A novel approach for target motion analysis (TMA), which uses conventional passive bearing together with multipath time-delay measurements is examined. This so-called "Multipath TMA" offers two tactical advantages over the classical bearings-only TMA: no requirement for any ownship maneuver, and a good performance in terms of estimation error achieved in a shorter time. Both known and unknown multipath cases are addressed. Finally, Monte-Carlo simulations and at-sea trials demonstrate the practical efficiency of such a multipath TMA. View full abstract»

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  • Detection and range/Doppler estimation for colocated sensors

    Publication Year: 1997 , Page(s): 825 - 834
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1488 KB)  

    The problem of multisensor detection and high resolution signal state estimation using joint maximum a posteriori detection and high order nonlinear filtering techniques is addressed. The model-based fusion approach offers the potential for increased target resolution in range/Doppler/azimuth space. The approach employs joint detection/estimation filters (JDEF) for target detection and localization. The JDEF approach segments the aggregate nonlinear model over the entire target resolution space into a number of localized nonlinear models by partitioning the resolution space into a number of resolution subcells. This partitioning leads to extremely accurate state estimation. The proposed JDEF approach has a built-in capability for automatic data alignment from multiple sensors, and can be used for centralized, decentralized, and distributed data fusion. View full abstract»

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  • Optimal nonlinear filtering in GPS/INS integration

    Publication Year: 1997 , Page(s): 835 - 850
    Cited by:  Papers (36)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1754 KB)  

    The application of optimal nonlinear/non-Gaussian filtering to the problem of INS/GPS integration in critical situations is described. This approach is made possible by a new technique called particle filtering, and exhibits superior performance when compared with classical suboptimal techniques such as extended Kalman filtering. Particle filtering theory is introduced and GPS/INS integration simulation results are discussed. View full abstract»

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  • Optimizing Murty's ranked assignment method

    Publication Year: 1997 , Page(s): 851 - 862
    Cited by:  Papers (12)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2243 KB)  

    We describe an implementation of an algorithm due to Murty for determining a ranked set of solutions to assignment problems. The intended use of the algorithm is in the context of multitarget tracking, where it has been shown that real-time multitarget tracking is feasible for some problems, but many other uses of the algorithm are also possible. The following three optimizations are discussed: (1) inheriting dual variables and partial solutions during partitioning, (2) sorting subproblems by lower cost bounds before solving, and (3) partitioning in an optimized order. When used to find the 100 best solutions to random 100×100 assignment problems, these optimizations produce a speedup of over a factor of 20, finding all 100 solutions in about 0.6 s. For a random cost matrix, the average time complexity for finding k solutions to random N×N problems appears to be nearly linear in both k and N, for sufficiently large k. View full abstract»

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  • Bias compensation and tracking with monopulse radars in the presence of multi path

    Publication Year: 1997 , Page(s): 863 - 882
    Cited by:  Papers (15)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2029 KB)  

    The problem of tracking targets in the presence of reflections from sea or ground is addressed. Both types of reflections (specular and diffuse) are considered. Specular reflection causes large peak errors followed by an approximately constant bias in the monopulse ratio, while diffuse reflection has random variations which on the average generate a bias in the monopulse ratio. Expressions for the average error (bias) in the monopulse ratio due to specular and diffuse reflections and the corresponding variance in the presence of noise in the radar channels are derived. A maximum maneuver-based filter and a multiple model estimator are used for tracking. Simulation results for five scenarios, typical of sea skimmers, with Swerling III fluctuating radar cross sections (RCSs) indicate the significance and efficiency of the technique developed in this paper-a 65% reduction of the rms error in the target height estimate. View full abstract»

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  • Multiple hypothesis track maintenance with possibly unresolved measurements

    Publication Year: 1997 , Page(s): 883 - 892
    Cited by:  Papers (52)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1179 KB)  

    In surveillance problems dense clutter/dense target situations call for refined data association and tracking techniques. In addition, closely spaced targets may exist which are not resolved. This phenomenon has to be considered explicitly in the tracking algorithm. We concentrate on two targets which temporarily move in close formation and derive a generalization of MHT methods on the basis of a simple resolution model. View full abstract»

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  • Effects of ionospheric scintillation on differential demodulation of GPS data

    Publication Year: 1997 , Page(s): 893 - 902
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    Global Positioning System (GPS) receivers that must operate under fading propagation conditions can use differential phase-shift keying (DPSK) and reference bits to reliably demodulate GPS data. The demodulation performance of such receivers is analyzed for nonfading and Rayleigh fading channels. Theoretical results derived here are compared with measured error rates taken during scintillation testing of a prototype GPS/DPSK receiver. View full abstract»

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  • MMAE/MMAC control for bending with multiple uncertain parameters

    Publication Year: 1997 , Page(s): 903 - 912
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1542 KB)  

    A moving-bank multiple model estimator/controller (MMAE/MMAC) based on linear system, quadratic cost, and Gaussian noise (LQG) assumptions is used to quell unwanted vibrations in a simulated large flexible space structure. The structure, known as the Space Integrated Controls Experiment (SPICE), exists at Phillips Laboratory, Kirtland Air Force Base, New Mexico. The structure consists of a large platform and a smaller platform connected by a tripod of flexible legs. The purpose of the control system is to maintain a very precise line-of-sight (LOS) vector through the center of the spacecraft. Kalman filtering, used to estimate the position and velocity of the bending modes of the structure, and LQG control techniques are the primary design tools used in the MMAE/MMAC algorithms. Implementing a parallel bank of filters increases robustness when uncertainties exist in the system model, here specifically allowing adaptation to uncertain and changing undamped natural frequencies of the bending modes of the structure. A moving-bank algorithm is utilized to reduce the computational loading. The MMAE/MMAC design provides a well-suited method of estimating variations in the vector of undamped natural frequencies and quelling vibrations in the structure. The MMAE/MMAC was able to track numerous parameter changes and jumps while providing adequate control for the structure. View full abstract»

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  • PWM converter with low stresses and zero capacitive turn-on losses

    Publication Year: 1997 , Page(s): 913 - 920
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1513 KB)  

    A buck converter operating at constant switching frequency, whose active switches and recovery diode commutate at zero-voltage-switching (ZVS), with zero capacitive turn-on losses, is proposed. By using the parasitic capacitances of the switches as resonant capacitors, multiresonance is created. The resonant stage takes place only after the resonant inductor has been discharged, thus avoiding a resonant current peak; the devices are subjected to the same stresses as their counterparts in conventional hard-switching converters. A high efficiency is obtained. View full abstract»

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  • Detecting near collisions for satellites

    Publication Year: 1997 , Page(s): 921 - 929
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (775 KB)  

    A highly efficient algorithm is presented for detecting near collisions involving satellites. Rather than examine all possible pairings of a satellite with another orbiting object, the new approach examines trajectories at a sequence of coarse time steps. Objects which are spatially isolated cannot be involved in a collision, and are discarded. The time steps, orbit calculations, and discarding are repeatedly refined until the only remaining objects experience near collisions. View full abstract»

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  • A maximum power transfer battery charger for electric vehicles

    Publication Year: 1997 , Page(s): 930 - 938
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1466 KB)  

    A battery charger is described that uses an on-line microcontroller to maximize its output power. This is done by always operating at either the maximum allowable input current or the thermal limit imposed by the charger itself. In this case the thermal limit is determined by the junction temperatures of the two main insulated gate bipolar transistors (IGBTs). Since direct measurement of these temperatures is impractical, they must be calculated by a computer algorithm that uses various on-line measurements. Experimental results for an 8 kW charger indicate a reduction in the bulk charging time of about 26% when used with a set of NiFe batteries. View full abstract»

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  • Frequency-controlled series-resonant converter with synchronous rectifier

    Publication Year: 1997 , Page(s): 939 - 948
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2070 KB)  

    This paper presents an analysis and experimental results for a frequency-controlled series-resonant dc-dc converter that consists of a Class-D zero-voltage-switching (ZVS) series-resonant inverter and a center-tapped synchronous rectifier. If the dc output voltage is low, the efficiency of the converter is dominated by the efficiency of the rectifier. Low on-resistance metal-oxide-semiconductor field-effect transistors (MOSFETs) are used in the rectifier instead of diodes because the forward voltage drop across the rectifying device is low, resulting in a high efficiency. The dc output voltage is regulated against variations in the load resistance and the dc input voltage by varying the operating frequency. Experimental results are presented for a converter with a dc input voltage of 150 V, an output voltage of 5 V, and a dc load resistance ranging from 0.5 to 5.5 R. The measured efficiency was 86% for a 50 W output and 89% for a 25 W output. The theoretical results were in good agreement with the measured results. View full abstract»

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  • Optimal pure proportional navigation for maneuvering targets

    Publication Year: 1997 , Page(s): 949 - 957
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1358 KB)  

    The optimal pure proportional navigation (PPN) guidance law with time-varying navigation gains is considered. Unlike the conventional optimal PPN approach where linearized model was assumed in the optimization process, this work exploits the exact nonlinear formulation of PPN to derive analytically the optimal time trajectory of the navigation gain to minimize a performance index which is a weighted sum of the final time and the integral of the squared acceleration. It is verified that the PPN scheme with constant navigation gain is not only optimal in the vicinity of the interception point, but also optimal for the whole trajectory, if the navigation constant is designed by the methodology proposed here. Based on the optimization results for nonmaneuvering targets, a recursive optimal PPN scheme is proposed for maneuvering targets, wherein the optimal navigation gain and time-to-go are predicted recursively during the interception, and trajectory and performance of the interceptor guided by optimal recursive PPN scheme are evaluated analytically. View full abstract»

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  • A relative navigation system for formation flight

    Publication Year: 1997 , Page(s): 958 - 967
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1329 KB)  

    A relative navigation system based on both the Inertial Navigation System (INS) and the Global Positioning System (GPS) is developed to support situational awareness during formation flight. The architecture of the system requires an INS/GPS integration across two aircraft via a data link. A fault-tolerant federated filter is used to estimate the relative INS errors based on relative GPS measurements and a range measurement obtained from the data link. The filter is constructed based on a reduced-order model of the relative INS error process. A method for analyzing the filter performance is presented. A case involving two helicopters in formation flight is studied under three different night trajectories to account for the effect of vehicle motion on the INS state transition matrix. The results of the covariance analysis are compared with actual night results over an instrumented test range. View full abstract»

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  • Development of GPS-based attitude determination algorithms

    Publication Year: 1997 , Page(s): 968 - 976
    Cited by:  Papers (13)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2687 KB)  

    This paper describes two Global Positioning System (GPS) based attitude determination algorithms which contain steps of integer ambiguity resolution and attitude computation. The first algorithm extends the ambiguity function method to account for the unique requirement of attitude determination. The second algorithm explores the artificial neural network approach to find the attitude. A test platform is set up for verifying these algorithms. View full abstract»

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  • Eigenanalysis for interference cancellation with minimum redundancy array structure

    Publication Year: 1997 , Page(s): 977 - 988
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    In a previous work, the principles of the eigenanalysis method for interference cancellation was studied for uniform regular array (URA) structure, wherein the array elements are equally spaced. The main objective of this paper is to extend the results of that work to adaptive arrays with different geometry termed "minimum redundancy array" (MRA). An efficient method is presented to solve the minimum variance optimization problem and explicit analytical solutions are derived for the optimal weight vector and output noise variance of the eigencanceler. Performance analysis of the general N-element array was first derived and used to extract the performance of MRA. URA is also considered as a special case. The closed-form equation depicts the minimum variance noise residue for the single interference case, while an interactive procedure is suggested for the two interferences case. If there are more than two interferences, we propose to use direct numerical calculation. View full abstract»

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  • Asymptotic distribution of the conditional signal-to-noise ratio in an eigenanalysis-based adaptive array

    Publication Year: 1997 , Page(s): 988 - 997
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (358 KB)  

    The statistical characterization of the conditioned signal-to-noise ratio (SNR) of the sample matrix inversion (SMI) method has been known for some time. An eigenanalysis-based detection method, referred to as the eigencanceler, has been shown to be a useful alternative to SMI, when the interference has low rank. In this work, the density function of the conditioned SNR is developed for the eigencanceler. The development is based on the asymptotic expansion of the distribution of the principal components of the covariance matrix. It is shown that, unlike the SMI method, the eigencanceler yields a conditional SNR distribution that is dependent on the covariance matrix, It is further shown that simpler, covariance matrix-independent approximations can be found for the large interference-to-noise case. The new distribution is shown to be in good agreement with the numerical data obtained from simulations. View full abstract»

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  • Blind identification and separation of convolutively mixed independent sources

    Publication Year: 1997 , Page(s): 997 - 1002
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (130 KB)  

    A trispectra method for solving the m-input n-output (n≥m) wideband blind identification and signal separation problem with unknown number of sources m is presented. The method is universal in the sense that it does not impose any restriction on the probability distribution of the input signals provided that they are non-Gaussian. A criterion, which states a sufficient condition for identification and separation, has been proved. An algorithm is also developed based on the criterion, whose efficiency is verified by the simulations. View full abstract»

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  • Optimal number of phased array faces and signal processors for horizon surveillance

    Publication Year: 1997 , Page(s): 1002 - 1006
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (243 KB)  

    The problem of the optimal number of phased array faces for performing 360° horizon surveillance is considered. Assuming the detection performance is the same in all beam positions and the total number of T/R modules is constant, it is shown that the optimal number of array faces is three. This is true whether the arrays are operating simultaneously or sequentially. A parametric analysis is performed between the number of array faces operating simultaneously and the associated cost of simultaneous operation in terms of the size of the array. View full abstract»

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Aims & Scope

IEEE Transactions on Aerospace and Electronic Systems focuses on the equipment, procedures, and techniques applicable to the organization, installation, and operation of functional systems designed to meet the high performance requirements of earth and space systems.

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Meet Our Editors

Editor-in-Chief
Lance Kaplan
Army Research Laboratory