与空时二维自适应滤波兼容的单脉冲测角新方法

针对机载相控阵雷达系统提出了一种空时二维自适应单脉冲测角方法 ,当存在阵元和通道幅相误差时它仍具有较高的测角精度。还给出了一种稳健的自适应和、差波束增益归一化方法 ,并讨论了所提方法的简化兼容实现方案。最后给出了基于高保真雷达杂波模拟数据的仿真实验结果     

机载雷达中的单脉冲技术

 本文总结机载雷达中单脉冲技术的研究和应用,着重讨论幅度比较系统的关键技术,给出有关数据。 机载雷达中的单脉冲技术着眼于抗干扰性能和特殊应用。这些应用包括空对地测距、角分辨力改进、地形防撞。本文阐述了这些特殊应用。     

相控阵雷达导引头波束稳定技术研究

 相控阵雷达导引头已成为新型空空导弹制导系统的首选,相控阵雷达导引头应用在空空导弹上需要首先解决导引头波束稳定的技术难题。本文基于波束指向在惯性空间不变性原理提出一种相控阵雷达导引头波束稳定算法,对影响相控阵雷达导引头隔离度性能的主要因素进行了仿真分析。仿真结果表明:该算法可以实现相控阵雷达导引头波束惯性空间指向稳定并且满足工程应用要求;通过减小速率陀螺数据周期和波束控制周期,及引入速率陀螺传输延时补偿算法可以提高导引头的隔离度性能。     

An Analysis of Wide-Band Microwave Monopulse Direction-Finding Techniques

This paper presents the concept, theory of operation, characteris tic equations, and error analysis of four wide-band monopulse techniques. The basic techniques described, which include pure amplitude monopulse, phase and amplitude monopulse (two-and three-channel configurations), and pure phase monopulse interferometer, are particularly applicable to monopulse direction finding systems that require frequency coverage over several octaves and open-loop angle bearing of several degrees. Sufficient detail and working formulas are included to permit a trade-off analysis to be made between the direction-finding techniques for selection in specific hardware applications.     

Satellite Tracking Simultaneous-Lobing Monopulse Receiving System with Polarization Diversity Capability

A 136-MHz to 10-GHz simultaneous-lobing monopulse receiving system, utilizing polarization diversity in both coherent (phase-lock) and noncoherent (nonphase-lock) operational modes, has been developed for the National Aeronautics and Space Administration (NASA) Space Tracking and Data Acquisition Network (STADAN). This sum-and-difference monopulse system, called APDAR (Advanced Polarization Diversity Autotrack Receiver), utilizes a maximalratio polarization diversity combining technique that matches the receiving antenna polarization to the incoming variable polarization from a spin-stabilized or tumbling satellite. Autotrack performance becomes independent of the incoming polarization orientation by continuous in-phase addition of the carrier-signal components from orthogonal antenna elements. This technique relies upon the principle that fading does not occur simultaneously on oppositely polarized receiving channels. APDAR results in improved autotrack performance by eliminating adverse effects of severe (over 30-dB) cross-polarization fading. The predetection diversity combining technique employed provides an average 3-dB signal-to-noise (SNR) improvement. This paper describes a series of 136-MHz satellite tracking tests and analyzes a maximal-ratio predetection diversity combiner, a three-loop phase-lock loop system, and a frequency-switched radiometer.     

Monopulse Resolution of Interferometric Ambiguities

Ambiguities in interferometers with high angular accuracy must be resolved to achieve a practical system design. A new technique for ambiguity resolution is described and is based on monopulse circuitry used with the interferometric elements. The overall angular accuracy of the system is achieved by the interferometer; the angular accuracy of the monopulse subsystem is used to resolve interferometric ambiguities. An expression for the probability of correct ambiguity resolution is derived as a function of element size and monopulse accuracy which indicates that high probability of ambiguity resolution results when the size of the interferometric elements are a fraction of the interferometric baseline. Finally, a comparison between conventional monopulse and interferometric system designs is made for the three principal parameters, signal sensitivity, angular accuracy, and field of view, that dictate the appropriate choice for a particular application. Interferometric systems are more appropriate than monopulse systems for those applications in which angular accuracy and field of view are more important than signal sensitivity.     

Monopulse Radars Excited by Gaussian Signals

This paper presents the theoretical probability densities of the outputs of both an amplitude-comparison monopulse radar and a phase-comparison monopulse radar when the monopulse radars are excited by Gaussian signals plus Gaussian noises. These probability densities are useful for studying the responses of monopulse radars to noise excitations. For example: Noise excitations arise when the monopulse radars are ?viewing? a noise source or a radar target consisting of randomly moving scatterers. The probability densities also serve as useful approximations for characterizing the outputs of monopulse radars when sinusoidal signals plus Gaussian noises excite the monopulse radars. Some special cases of the probability densities are presented in graphs.     

Monopulse-radar angle tracking in noise or noise jamming

In many monopulse radars, feedback in the angle-tracking servo system is taken to be directly proportional to the monopulse ratio. In those radars, monopulse measurements are conditioned on simultaneous occurrences of receiver sum-channel video exceeding a detection threshold: if a detection fails to occur, the measurement is ignored, and the angle-tracking servo is made to coast. Such conditioning is shown to be necessary in order that the noise power be finite in the servo feedback. The conditional mean value and conditional variance of the monopulse ratio are derived and quantified in terms of threshold level as well as signal-to-noise ratio. The formulation permits the noise covariance between receiver difference and sum channels to be complex rather than only real-valued, so that the sources of noise jamming are not required to be positioned in the receiving-antenna mainlobe and to be copolarized with the antenna response there. Nonfluctuating and Rayleigh-fluctuating target cases are considered and compared, and fluctuation loss is quantified     

Accuracy of angle estimation with monopulse processing using twobeams

Expressions are provided for the accuracy of monopulse angle estimation using two beams. It is shown that, if the signal angle is halfway between the angles of the beams, the Cramer-Rao lower bound (CRLB) for monopulse processing is almost as small as the CRLB obtained if the entire array of sensors is used. The monopulse CRLB is considerably poorer if the angle of the signal is equal to that of one of the two beams. The expressions in this correspondence are for a uniformly weighted linear array of M equally spaced sensors, for which N⩾M beams are formed     

An Application of Radiometric Techniques to Precision Angle Tracking Radar Systems

A new technique is described which provides for precision angle tracking of celestial radio sources with a conventional monopulse antenna receiving system. It is shown that this technique is readily adapted to angle tracking radars. The features of conventional monopulse operation are preserved while permitting precise angle tracking of noise sources when signal to noise ratios are much less than unity. Measurements, using a four-horn monopulse feed with a 28-foot parabolic reflector and a "monopulse radiometer" produced the characteristic monopulse angle detection functions when using the sun, the moon, and Cassiopeia A as boresight reference sources. Precision measurements were made to 8 arc second under varying weather conditions using 28-foot radio astronomy antennas. The accuracy of the measurements were limited by the antenna angle encoders, consequently no conclusions are drawn with regard to the absolute accuracy of the measurements. The celestial coordinates of four discrete radio sources and the equations for coordinate transformation to local elevation and azimuth are contained in the Appendixes.     

反向交叉眼对单脉冲雷达干扰效果分析及仿真验证

交叉眼干扰被认为是对单脉冲雷达干扰最有效的方式之一。基于雷达方程建立了隔离平台回波下的两点源反向交叉眼干扰模型，推导了交叉眼干扰欺骗角一般性公式，研究了干扰机发射天线间距、干扰平台旋转角和干扰机相对雷达之间距离等参数变化对角度欺骗效果的影响，并依据单脉冲雷达接收机获取角度的信息处理流程，建立了单脉冲雷达接收机仿真模型，对交叉眼数学模型的正确性和局限性进行了分析。研究结果表明：单脉冲雷达越靠近两点源交叉眼干扰机中心线、干扰机两发射天线间距越大、与干扰机距离越近时，角度欺骗效果越好；单脉冲雷达的欺骗角度随着与干扰机距离的接近呈指数式增大；数学模型和仿真模型计算的单脉冲雷达角度误差最大值随干扰机天线与雷达天线中心连线的夹角的增大呈指数化增长。研究可为交叉眼干扰工程设计作参考。     

Radar measurement extraction in the presence of sea-surface multipath

In the presence of sea-surface multipath monopulse radar signals from a low elevation target have three alternative paths in addition to the direct (radar-to-target) path due to reflections from the sea surface. The specular reflection causes significant signal fading. The diffuse reflection causes an approximately constant bias to the in-phase component of the monopulse ratio, which is the standard extractor of the direction of arrival (DOA) in the monopulse processing. The diffuse reflection also causes higher standard deviation to the in-phase component of the monopulse ratio. We propose a maximum likelihood (ML) angle extraction technique for low elevation targets of known average signal strength having a Rayleigh fluctuation. The results show that this method reduces the error of the estimated angle compared with the conventional monopulse ratio estimator. Subsequently, the ML angle extractor is modified for the unknown average signal strength case. This modified angle extractor has only a small performance degradation compared with the known average signal strength case, but it performs much better than the monopulse ratio based estimator. An algorithm to calculate the accuracy of the estimated angle (or height) is also presented. This angle extractor reduces the root-mean-square error (RMSE) by more than 50% in the signal processing stage when used in a low flying target tracking scenario. The same algorithm can be used to track sea skimmers.     

Performance Analysis of Monopulse Receivers for Secondary Surveillance Radar

In modern secondary surveillance radar (SSR) the monopulse technique is currently introduced for the measurement of the azimuth of the targets. The monopulse technique is based on a suitable processing of signals received by a multiple antenna. In SSR the signals are generated by a transponder on the aircraft as replies to interrogations from ground equipment, and consist of trains of pulses. The monopulse measurements can be carried out on the basis of a single pulse from each train, so that it provides a great number of azimuth estimates. Many monopulse measurement devices exist, corresponding to different processing techniques. From the point of view of accuracy and precision, their behaviors differ with respect to the sources of errors, both internal (noise and imperfect calibrations) and external (interference and propagation effects). The four main types of monopulse receivers are analyzed here with respect to the effects of the internal error sources on the resulting measurement accuracy. After an introductory discussion of the performances of the receivers, a detailed analysis is carried out on the basis of a general mathematical model. The results are given in an analytical form and in some comprehensive diagrams.     

Correlation between horizontal and vertical monopulse measurements

Many radar systems use the monopulse ratio to extract angle of arrival (AOA) measurements in both azimuth and elevation angles. The accuracies of each such measurement are reasonably well known: each measurement is, conditioned on the sum-signal return, Gaussian-distributed with calculable bias (relative to the true AOA), and variance. However, we note that the two monopulse ratios are functions of basic radar measurements that are not entirely independent, specifically in that the sum signal is common to both. The effect of this is that the monopulse ratios are dependent, and a simple explicit expression is given for their correlation; this is of considerable interest when the measurements are supplied to a tracking algorithm that requires a measurement covariance matrix. The system performance improvement when this is taken into account is quantified: while it makes little difference for a tracking radar with small pointing errors, there are more substantial gains when a target is allowed to stray within the beam, as with a rotating (track-while-scan) radar or when a single radar dwell interrogates two or more targets at different ranges. But in any case, the correct covariance expression is so simple that there is little reason not to use it. We additionally derive the Cramer-Rao lower bound (CRLB) on joint azimuth/elevation angle estimation and discover that it differs only slightly from the covariance matrix corresponding to the individual monopulse ratios. Hence, using the individual monopulse ratios and their simple joint accuracy expression is an adequate and quick approximation of the optimal maximum likelihood procedure for single resolved targets.     

Self-calibrating SSR monopulse receiver

An extension of the monopulse technique for estimating the target azimuth in a secondary surveillance radar (SSR) is considered. The idea is to associate in pairs monopulse measurements coming from the amplitude processor (AP) at the dwell time processing level. This allows the automatic compensation of the bias errors due to the misalignments in the receiver channels, thus eliminating the necessity for periodic system calibration. This dual-pulse technique also allows for the practical use of the dot product receiver as a modification of the AP receiver. This, in turn, implies that the variance of each dual-pulse estimate is uniformly maintained at the monopulse maximum-likelihood level over the whole off-boresight angle (OBA) range     

Maximum likelihood angle extractor for two closely spaced targets

In a scenario of closely spaced targets special attention has to be paid to radar signal processing. We present an advanced processing technique, which uses the maximum likelihood (ML) criterion to extract from a monopulse radar separate angle measurements for unresolved targets. This processing results in a significant improvement, in terms of measurement error standard deviations, over angle estimators using the monopulse ratio. Algorithms are developed for Swerling I as well as Swerling III models of radar cross section (RCS) fluctuations. The accuracy of the results is compared with the Cramer Rao lower bound (CRLB) and also to the monopulse ratio technique. A novel technique to detect the presence of two unresolved targets is also discussed. The performance of the ML estimator was evaluated in a benchmark scenario of closely spaced targets - closer than half power beamwidth of a monopulse radar. The interacting multiple model probabilistic data association (IMMPDA) track estimator was used in conjunction with the ML angle extractor     

Model-based multifrequency array signal processing for low-angletracking

Tracking low-altitude targets over the sea is problematic because of interference between the direct and reflected signal. Standard monopulse trackers can experience large errors because of multipath maximum likelihood estimation (MLE) has been used to more accurately estimate the target height in the presence of multipath MLE is a model-fitting technique where the model parameters are chosen to maximize the likelihood function. It is shown that the type of observation model has a large effect on performance. Tracking performance is compared using three different observation models employing varying amounts of a priori information. Results are presented for different array sizes: eight and 32-element arrays and two-element subarrays typical of phase monopulse. Performance is compared with that of standard techniques such as Fourier beamforming and phase monopulse     

Monopulse radar based on spatiotemporal correlation of stochastic signals

The theory and technique of angle-of-arrival (AOA) estimation using random-noise or other stochastic transmit waveforms is addressed. The additional uncertainties induced by signal itself and the statistical complexity of the received signals result in major challenges. The statistical properties of the random-noise interferometer and monopulse radar system are studied and compared theoretically using an approximation method. Furthermore, a random-noise coherent correlation receiver (CCR) architecture is proposed. The concept of mean monopulse characteristic curve (MMCC) is introduced. Experimental results using an X-band random-noise monopulse radar system validate the theoretical predictions of random-noise monopulse characteristics and suggest potential applications such as surveillance, imaging, and maneuvering target tracking.     

Adaptive digital beamforming for angle estimation in jamming

A radar digital beamforming (DBF) architecture and processing algorithm is described for nulling the signal from a mainlobe electronic jammer and multiple sidelobe electronic jammers while maintaining monopulse angle estimation accuracy on the target. The architecture consists of a sidelobe jamming (SLJ) cancelling adaptive array (AA) followed by a mainlobe jamming (MLJ) canceller. A mainlobe maintenance (MLM) technique or constrained adaptation during the sidelobe cancellation process is imposed so that the results of the SLJ cancellation process do not distort the subsequent mainlobe cancellation process. The SLJ signals and the MLJ signals are thus cancelled sequentially in separate processes. This technique was developed for improving radar processing in determining the angular location of a target, and specifically for improving the monopulse technique by maintaining the accuracy of the target echo monopulse ratio in the presence of electronic jamming by adaptive suppression of the jamming signals before forming the monopulse sum and difference beams