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One of the few electronic attack techniques that can deceive radars in angle is cross-eye jamming, which mimics the naturally-occurring phenomenon glint. The extreme tolerance requirements of cross-eye jamming mean that a retrodirective implementation is required, but published measurements of cross-eye jamming either ignore the retrodirective implementation or only simulate it. The implementation of a retrodirective cross-eye jammer and its testing against a monopulse radar are described. A procedure for calibrating the jammer is outlined and is shown to be effective by achieving large angular errors. The measured results agree well with the extended analysis of cross-eye jamming and confirm that the implemented jammer is retrodirective. Specifically, the ability of a cross-eye jammer to generate an indicated angle that never becomes zero, thereby potentially breaking a tracking lock, is confirmed. [ABSTRACT FROM AUTHOR]

This article proposes an accurate clutter synthesis method for a dynamic radar under various environmental conditions. Previous clutter synthesis methods mostly rely on empirical clutter models fitting the measurement results obtained from the limited conditions of observations. Inherently, these models have difficulties synthesizing clutter for unexplored environments and operational conditions. The method presented in this article overcomes this limitation by creating and summing the clutter patch by patch. The clutters of individual patches are synthesized by the clutter model corresponding to each patch's specific conditions, such as the grazing angle, ground texture, and wind velocity. It enables one to synthesize clutter signals under various observation scenarios accurately. For example, this work demonstrates the synthesis of clutter signals from heterogeneous textures for an aircraft radar on a mission. Also, the clutter signals for a monopulse radar are synthesized and included in the radar simulation to evaluate the performance of a detection algorithm. Potentially, this method can be utilized to design a robust radar algorithm against the clutter environment of interests. For a given condition of measurement, it is shown that the synthesized clutters agree well with the actual measured data in their statistical characteristics. The program is freely available through the open code. [ABSTRACT FROM AUTHOR]

Diversity smoothing has been widely used for angle estimation with multiple input multiple output (MIMO) radar in the presence of coherent or correlated targets, and the parameter identifiability is an interesting issue. Previous works have shown sufficient conditions for some special cases, such as the coherent targets with conventional MIMO radar, and the array size are derived as a function of the target number and target structure. In this article, we further introduce the interelement spacings to build a complete parameter identifiability scheme. For monostatic MIMO radars, the antenna numbers and interelement spacings of transmit and receive arrays are derived as functions of the target number and the target structure. The optimization models are built to calculate the maximum number of detectable targets for a given target structure. Additionally, the conditions for the bistatic MIMO radar are derived from two-dimension viewpoint. It is shown that the new results improve upon previous spatial smoothing or diversity smoothing methods and recover them in special cases. Simulation results are presented that corroborate our theoretical findings. [ABSTRACT FROM AUTHOR]

Randomized stepped-frequency (RSF) radar, which transmits pulses with random carrier frequencies in a coherent processing interval, has an excellent electronic counter-countermeasures performance and the ability to generate the high-range-resolution profiles (HRRPs) of target with a narrow bandwidth receiver. Due to the random nature, the choice of carrier frequencies in RSF radar is usually an undersampling of available frequencies, which make the HRRP generated by matched filtering suffer from high noise-like sidelobes. In this article, we take the sinc-envelopes formed by linear-frequency-modulation pulses as well as RSF phases into account, and propose a novel (or generalized) range sidelobe suppression filters design method for RSF chirp waveform based on convex optimization (the model is transformed into a second-order cone program). By using these filters, the target HRRP with much lower sidelobes can be obtained, and the performance can be traded with the instantaneous bandwidth of the receiver, which provides a new idea for solving the sidelobe problem in RSF radar. [ABSTRACT FROM AUTHOR]

The effect of the radar skin return from the platform on which a cross-eye jammer is mounted is significant in many practical cross-eye jamming scenarios. However, all published analyses of skin-return affected cross-eye jamming have significant limitations. These limitations are addressed by deriving equations for the distribution of the cross-eye gain in the presence of skin return. The values of these results are demonstrated by using them to gain insight into how skin return affects cross-eye jamming. [ABSTRACT FROM AUTHOR]

This paper investigates the problem of angle measuring of the target in the presence of jammings with planar arrays. The relationship between the quiescent monopulse ratios and azimuth/elevation is first studied. On this basis, the distortion of the surface of the conventional minimum variance distortionless response monopulse ratio is analyzed. In order to avoid such distortion and approximate the adaptive monopulse ratio surface to the quiescent one, an adaptive monopulse approach with joint linear constraints on both the azimuth and elevation is proposed. Simulation results demonstrate that the proposed approach is capable of attaining a high angle measuring accuracy in the presence of mainlobe jammer. [ABSTRACT FROM AUTHOR]

When a monopulse radar is subjected to main-lobe barrage interference, the target and the interference source are both located within the 3 dB beamwidth of the radar; the target returns are subsumed by the interference, which results in incorrect detection, erroneous angle measurements, and tracking error. Based on a hybrid polarimetric monopulse radar with six channels, a new approach is presented for estimating the target angle from a single snapshot in the presence of main-lobe barrage interference. By means of polarization filtering and polarization synthesis of signals from multiple channels with two orthogonal polarizations, a new pair of sum and difference signals is formed that represents the angle difference between the target and the interference source. After standard monopulse processing of these new signals and additional compensation, the estimate of the target angle is derived with low computational complexity. [ABSTRACT FROM AUTHOR]

The monopulse angle-estimation technique used in digital beamforming radars is investigated from the perspective of optimizing the angle accuracy. Specifically, a digital difference beamforming taper is proposed in this paper to optimize the monopulse angle accuracy. For a fully digitized array radar with an amplitude-tapered antenna aperture for sum beampattern with low sidelobes, the monopulse angle accuracy obtained using the proposed difference taper coincides with the Cramer–Rao lower bound. The derivation of the monopulse angle accuracy with the proposed difference taper is presented and an improvement of the accuracy over the conventional monopulse accuracy is proved theoretically. The results of computer simulations using a uniform linear array is included to highlight the accuracy improvement by a factor of 1.16 (over the conventional monopulse), which is equivalent to a 1.3 dB reduction in the signal-to-noise ratio for the requisite angle accuracy. [ABSTRACT FROM AUTHOR]

In the presence of the interference from a main-lobe direction, the monopulse measurements always get erroneous angle estimates. By polarization filtering, the interference can be suppressed. However, an error from the cross-polarization of the target and the unpolarized component of the interference is introduced in the monopulse processing. To effectively extract the angle of the extended target accurately after polarization filtering, duplex polarization filtering and polarization filtering extractor based on a covariance matrix are developed. In addition, it can be found that the variance of the angle estimates varies when the polarizations of the target and the interference fluctuate, which degrades the performance of the tracking filter. For this problem, an adaptive fixed-gain filter for stabilizing the variance of the target angle estimates is proposed. [ABSTRACT FROM AUTHOR]

Tracking low-elevation targets over a smooth surface is challenging because of the multipath effect. The symmetrical difference pattern monopulse is proposed for low-angle tracking with array radar. At first, the optimal symmetrical difference pattern is designed. The proposed monopulse is implemented using symmetrical sum and difference patterns by digital beam forming. The monopulse ratio derived from the symmetrical sum and difference patterns is not affected by the multipath effect. Then, the performance of the symmetrical difference pattern monopulse is evaluated by simulations in terms of the signal-to-noise ratio, target elevation, and complex reflection coefficient. Field data sets acquired from a VHF array radar are used for validation. It is found that the measurement error is still less than 1/30th of a beamwidth when the target elevation is less than a quarter of a beamwidth. The proposed monopulse scheme is suitable for VHF array radar, for which the multipath effect is serious. [ABSTRACT FROM AUTHOR]

The paper analyzes how a sensor array's direction-finding accuracy may be degraded by any stochastic uncertainty in the sensors? complex value gains, modeled here as complex value Gaussian random variables. This analysis is via the derivation of the hybrid Cramer-Rao bound (HCRB) of the azimuth-elevation direction-of-arrival estimates. This HCRB is analytically shown to be inversely proportional to a multiplicative factor equal to one plus the variance of the sensors' gain uncertainty. This finding applies to any array grid geometry. The maximum a posteriori (MAP) estimator corresponding to this uncertain gain data model is also derived. Monte Carlo simulations demonstrate that this estimator approaches the lower bound derived. [ABSTRACT FROM PUBLISHER]

The simultaneous use of multiple retrodirective cross-eye jammers is analyzed for both the case where the jammer loops point in different directions and when they point in the same direction. In both cases, the use of multiple cross-eye jammer loops is shown to lead to significantly increased angular errors in the threat radar under certain conditions. Alternatively, the sum-channel return can be increased to reduce the jammer-to-signal ratio requirements for each jammer loop. [ABSTRACT FROM PUBLISHER]

Due to the additional degrees of freedom, multiple-element cross-eye jamming (MCJ) can reduce tolerance sensitivity and increase the effective sector angle. In this paper, we investigate multiple-element retrodirective cross-eye jamming (MRCJ) based on the retrodirective linear array. The monopulse error and cross-eye gain are derived via trigonometric approximations. Moreover, excellent performances of MRCJ in terms of induced angular error and tolerance requirements are demonstrated in simulation results. [ABSTRACT FROM PUBLISHER]

This paper presents an important improvement on Sherman?s method for angle estimation of two unresolved targets when using monopulse radar. The graphical or numerical solution for the 6th-order polynomial equation is replaced with a quadratic equation that has exact algebraic solutions for nonfluctuating or slowly fluctuating targets. The proposed method can also estimate the angle for a single target without ambiguity and can estimate the angles when two targets are positioned at the same azimuth or elevation angle, in contrast with previous techniques. The proposed method is validated using simulations. [ABSTRACT FROM AUTHOR]

In the area of array signal processing, direction of arrival (DoA) estimation is a widely studied topic. In this estimation process the noise subspace of the received signal covariance matrix is often utilized and obtained through numerical methods. We explicitly derive an algebraic expression of the noise subspace when the number of signal sources present is less than the number of elements of a uniform linear array (ULA). This expression of the noise subspace is then used to formulate a constrained minimization problem to obtain the DoAs of all the sources in a scene in the presence of spatially white noise of identical power. This noise subspace-based estimation (NISE) algorithm iteratively solves for each source's DoA, potentially yielding (depending on the number of iterations) lower complexity than existing DoA estimation algorithms, such as fast root-MUSIC (FRM), while exhibiting performance advantages for a low number of time samples and low signal-to-noise ratio (SNR). The convergence of NISE is then proven mathematically. In addition it is shown how NISE can readily incorporate prior knowledge into the DoA estimation process. [ABSTRACT FROM AUTHOR]

Sparse arrays are of great interest in practical applications owing to their enlarged array apertures, which enable us to achieve better performance in direction finding. A kind of linear sparse arrays (LSpAs) composed of multiple uniform linear subarrays (ULSAs) with gain/phase uncertainties is considered. The problem of direction-of-arrival (DOA) estimation using such kinds of arrays is addressed. In particular two different cases are studied. In the first case all ULSAs are well calibrated, whereas there are unknown gains/phases among them. Using a new ESPRIT-like method, we show that the DOAs can be estimated in closed form. Interestingly, it is found that the unknown gains/phases can also be estimated in closed form by taking advantage of the subspace principle. In the second case we consider a more general situation where some of the ULSAs themselves are suffering from unknown sensor gain/phase responses. Again, we exploit the ESPRIT algorithm and propose a new approach to DOA and gain/phase estimation using this class of arrays. In our proposed methods the unknown parameters (i.e., DOAs and gains/phases) are estimated in closed form without performing spectral search. Representative numerical results are demonstrated to assess the effectiveness of the methods. [ABSTRACT FROM AUTHOR]

It is desirable to limit the apparent target to one side of a retrodirective cross-eye jammer despite the variation caused by platform skin return. The relationship between the jammer parameters and the jammer-to-signal ratio (JSR) to ensure that this occurs is investigated. When this relationship is not satisfied, the proportion of the apparent targets generated on the opposite side of the jammer is determined. [ABSTRACT FROM AUTHOR]

In many radar applications extended targets appear together with point targets. An important problem in particular for tracking algorithms is to rapidly detect these extended targets and to determine their centroid and shape. In a previous paper we have developed and characterized estimators for the centroid and extension of an extended target based on the generalized monopulse ratio when the target is modeled as a number of independent Swerling I?II point scatterers. However, the Swerling I?II model is a very rough approximation for the behavior of a real complex target. The work presented here extends the statistical characterizations to mixtures of independent Swerling I?II point scatterers and deterministic Swerling 0 point scatterers which may, however, vary arbitrarily in time. Such a mixture of deterministic and stochastic scatter model is able to provide good approximations of real target radar cross sections. [ABSTRACT FROM AUTHOR]

Angular glint gives rise to random pointing errors, which can deteriorate the direction-of-arrival (DOA) estimation accuracy. In monopulse radars the glint manifests itself through a complex valued process known as the complex monopulse ratio (CMR). Physical and statistical properties of the glint are considered. It is proposed to use the Poynting vector formalism for the CMR physical interpretation. The complex probability density function (pdf) and correlation function of CMR are derived. [ABSTRACT FROM AUTHOR]

In many radar applications extended targets appear together with point targets. An important problem in particular for tracking algorithms is to rapidly detect these extended targets and to determine their centroid and shape. We present a detector for extended targets and maximum-likelihood (ML) estimators for the centroid and the extension which are based only on the outputs of the generalized monopulse ratio. The generalized monopulse ratio is based on the sum and difference beams generated from the digital outputs of arbitrary subarrays of a planar array. It is therefore applicable to various kinds of modern array antennas. The extended target is characterized by an ellipse in the azimuth-elevation plane. The statistical performance of the centroid and the extension estimators is characterized by analytically their mean and variance. Numerical simulations indicate that these statistical characterizations are accurate and that small extended targets can be detected early. The statistical performance measures can therefore also be used for parametric system studies. [ABSTRACT FROM AUTHOR]

Estimation of the direction of arrival (DOA) of a signal source by means of a monopulse estimation scheme is one of the oldest and most widely used high-precision techniques in operational tracking systems. Although the statistical performance of this estimation technique has been extensively investigated, it has never been analyzed from the viewpoint of the joint detection-estimation problem. As a consequence the historical form of the (detector-angle estimator) solution has become the usual form implemented in operational tracking systems and may restrict their accessible performance. Indeed, the application of the optimal detection theory reveals alternative (detector-angle estimator) solutions providing other relevant trade-offs in detection-estimation performances that are worth considering to optimize the performance of the tracking system according to the scenario. Both stochastic signal model (Rayleigh-type signal source) and deterministic signal model (signal source of unknown amplitude) have been investigated, leading to a novel but equally simple (detector-angle estimator) solution through which analytical statistical prediction has been derived. Comparison of detection-estimation performances of new and usual solutions is presented. [ABSTRACT FROM AUTHOR]

Detection and estimation of multiple unresolved targets with a monopulse radar is a challenging problem. For ideal single bin processing, it was shown in the literature that at most two unresolved targets can be extracted from the complex matched filter output signal. A new algorithm is developed to jointly detect and track more than two unresolved targets from a single detection with the help of tracking information. That is, the method involves the use of tracking information in the detection process. For this purpose, target states are transformed into detection parameter space, which involves high nonlinearities. In order to handle the nonlinearities, the particle filter, which has proven to be effective in nonlinear non-Gaussian estimation problems, is used as the basis of the closed loop system for tracking multiple unresolved targets. In addition to the standard particle filtering steps, the detection parameters corresponding to the predicted particles are evaluated using the nonlinear monopulse radar beam model. This in turn enables the evaluation of the likelihood of the monopulse signal given tracking data. Bayesian model selection is then used to find the correct detection event. The corresponding particle set is taken as the correct representation of the target posterior. A simulated amplitude comparison monopulse radar is used to generate the data and validate the joint detection and tracking of more than two unresolved targets. [ABSTRACT FROM AUTHOR]

This paper proposes a novel statistical prediction of monopulse errors [1] for a radar Swerling III-IV target embedded in noise or noise jamming where multiple observations are available. First, the study of the maximum likelihood estimator (MLE) of the complex monopulse ratio for a Swerling III-IV target embedded in spatially white noise allows us to extend the use of the MLE practical approximate form introduced by Mosca [2] for Swerling 0-I-II cases. Afterward, we derive analytical formulas for both the mean and variance of the MLE in approximate form conditioned by the usual detection step performed on the sum channel of a monopulse antenna. Last, we provide a comparison of target direction of arrival (DOA) estimation performance based on monopulse ratio estimation as a function of the Swerling model in the context of a multifunction radar. [ABSTRACT FROM AUTHOR]

A radio interferometer capable of azimuth-elevation direction finding for geosynchronous satellites has been developed. The interferometer has two small-diameter antennas and four movable planar mirrors. The movable mirrors reflect the microwaves from the satellite and guide them to the fixed receiving antennas. Two of the movable mirrors are mounted on a rotary arm, so that the baseline of the interferometer can rotate in the horizontal plane. This configuration enables the interferometer to eliminate phase-ambiguity problems and cable-phase errors, resulting in a direction finding accuracy of better than 0.01 deg in the Ku band. [ABSTRACT FROM AUTHOR]

Random-noise radar has been applied successfully to range measurement, velocity estimation and terrain/target imaging. For applications involving stationary targets, tong integration times and process averaging are easily tolerated. In situations where the target or radar platform moves at high speed, the impact of this relative motion on system design should be considered. This work addresses the statistical performance of a generic random-noise radar receiver and examines the inter-relationships between design parameters and performance tradeoffs. Complementing this examination, a random-noise monopulse system is also investigated as a possible architecture for real-time angle estimation. Simulations and numerical illustrations provide the basis of processor design and performance prediction. [ABSTRACT FROM AUTHOR]

A novel closed-form solution to resolve the directions of arrival (azimuth and elevation) of two sources using a single snapshot (monopulse) of four independent channels is presented. Both phase comparison monopulse and amplitude comparison monopulse are solved. Exceptions where the two targets cannot be resolved are also discussed. Numerical simulation result of a practical phased-array configuration validates the effectiveness of the new solution. [ABSTRACT FROM AUTHOR]

Examines the correlation between horizontal and vertical monopulse measurements. Use of the monopulse ratio to extract angle of arrival measurements in both azimuth and elevation angles; Accuracies of the measurement; Dependency of the monopulse ratios.

Presents moving target detection and imaging results for an X band spotlight synthetic aperture radar (SAR) system that utilizes an along-track monopulse configuration for its data collection. Along-track monopulse SAR system geometry in two-dimensional slant-range and cross-range domain; Signal subspace processing for moving target detection; Motion estimation and moving target imaging.

Discusses the development of an advanced processing technique which uses the maximum likelihood criterion to extract from a monopulse radar separate angle measurements for unresolved targets. Key aspects of closely spaced target tracking; Angle extractor for two unresolved Rayleigh targets; Derivation of likelihood function for Rayleigh targets.

Focuses on a study which presented expressions for the accuracy of monopulse angle estimation using two beams. Information on the Cramer-Rao lower bound (CRLB) for monopulse processing; Details on the CRLB for Azimuth using the M sensors; Conclusions.

Presents the approaches to the processing of unresolved measurements as two direction-of-arrival (DOA) measurements for tracking closely space targets rather than the conventional single DOA measurement of the centroid. Probability distribution of the monopulse measurements for unresolved Rayleigh targets; Development of the Cramer-Rao lower bounds for the DOA estimation of unresolved Rayleigh targets.

Describes a radar digital beamforming architecture and processing algorithm for nulling the signal from a mainlobe electronic jammer and multiple sidelobe electronic jammers while maintaining monopulse angle estimation accuracy on the target. Features of the architecture; Derivation of a scheme for combining the adaptive array and mainlobe canceller for monopulse processing; Mainlobe maintenance techniques.

Reports on the development of the conditional probability density function (pdf) for each monopulse measurement of a Rayleigh target. Methodology used in study; Use of the conditional pdf to develop the conditional Cramer-Rao Lower Bound (CRLB); Concluding remarks on the study.

Presents a Neyman-Pearson algorithm for generalized maximum likelihood (GML) detection of the presence of multiple unresolved Rayleigh targets. Requirements of the algorithm; Performance and application of the algorithm; What simulations results revealed about the GML detection algorithm.

Calculates the joint distribution of the real and imaginary parts of the monopulse ratio (MR) for a monopulse radar, with arbitrarily correlated Gaussian noise and non-zero means in the sum and difference channels. Discussion of the general case of Gaussian channel noise; Thresholding with zero means; Use of the general result to develop the marginal density for the real part of the MR for the special case of real correlation between the channels.

Addresses the problem of tracking targets in the presence of reflections from sea or ground. Information on specular and diffuse reflection; Reference to specular reflection; Expressions for the average error bias.

Examines the performance of direction finding (DF) using two kinds of active interferometers in minimal configurations. Information on the active interferometers used; Results of a study of the Cramer-Rao bound on the estimation error of the bearing of a silent, nonradiating target.

A 2003 paper by Zheng, Tseng, and Yu presented closed-form solutions for the angles of arrival of returns from two targets when using four-channel monopulse radar. In this comment, we present a mathematically equivalent algorithm developed by Karl Baur in the 1970s that has a marginally lower computational complexity. Baur's work has remained largely unknown, because it was published in German and never translated into English. [ABSTRACT FROM AUTHOR]

Experimental measurements that accurately simulate the effect of a retrodirective cross-eye jammer on a monopulse radar are described. The accuracy of a recently published extended analysis of retrodirective cross-eye jamming and the limitations of the conventional phase-front analysis of cross-eye jamming are illustrated by the experiments. [ABSTRACT FROM AUTHOR]

We propose a multiple input multiple output (MIMO) radar system with widely separated antennas that employs monopulse processing at each of the receivers. We use Capon beamforming to generate the two beams required for the monopulse processing. We also propose an algorithm for tracking a moving target using this system. This algorithm is simple and practical to implement. It efficiently combines the information present in the local estimates of the receivers. Since most modern tracking radars already use monopulse processing at the receiver, the proposed system does not need much additional hardware to be put to use. We simulated a realistic radar-target scenario to demonstrate that the spatial diversity offered by the use of multiple widely separated antennas gives significant improvement in performance when compared with conventional single input single output (SISO) monopulse radar systems. We also show that the proposed algorithm keeps track of rapidly maneuvering airborne and ground targets under hostile conditions like jamming. [ABSTRACT FROM AUTHOR]

The matching required between the two directions through a retrodirective cross-eye jammer is considered using both the traditional phase-front analysis and an extended analysis. The design parameters to achieve a specified tracking error are derived and an optimal design is proposed. The results for the extended analysis show that the tolerances required to induce large angular errors in a monopulse radar are not as strict as the traditional analysis suggests. [ABSTRACT FROM AUTHOR]

Monopulse is an established array processing technique for fast and accurate angle estimation. This technique has been generalized to space-time array processing of any dimension. The statistical performance of this generalized monopulse parameter estimation has been characterized for several target fluctuation models but not for all cases. This gap is filled by this paper. We derive the mean and variance of the complex and real and imaginary part of the averaged monopulse ratio for all Swerling target models, deterministic targets (Swerling 0 case), \chi^2 distributed targets with 4 degrees of freedom (Swerling 3 or 4 case) including a given detection threshold, for an arbitrary number of difference beams, and for an arbitrary number of noncoherent averaging of time snapshots. For completeness we give also the already known results for Rayleigh targets (Swerling 1 or 2 case) in the same notation. From these means and variances, the performance of all kinds of parameter estimates with the generalized monopulse formula can be calculated. Applications of these statistical descriptions are presented for planar arrays and adaptive beamforming and for space-time adaptive processing (STAP) for broadband interference suppression. From these examples some interesting conclusions can be drawn. [ABSTRACT FROM AUTHOR]