Volterra Series Synthesis of Nonlinear Stochastic Tracking Systems

One of the most important objectives of a radar angle-tracking loop is to keep the target within the beamwidth of the radar antenna. Thus, the behavior of the antenna pointing error is of vital interest in determination of tracking performance. For a tracker with a general polynomial linearity (representing nonlinear receiver characteristics), subjected to constant line-of-sight rate inputs, random initial antenna pointing errors, and white Gaussian receiver noise, a method to obtain approximations to the transient mean and variance of the antenna pointing error as explicit functions of time is presented.     

Synthetic Aperture Radar System Design for Random Field Classification

The optimum design of synthetic aperture radar (SAR) systems intended to classify randomly reflecting areas, such as agricultural fields, characterized by a reflectivity density spectral density is studied. Assuming areas of known shape and location, the binary case, and a certain Gaussian signal field property, and ignoring interfield interference, the problem solution is given. The optimum processor includes conventional matched filter processing, but is nonlinear; a coherent optical system realization is outlined. The performance is approximated using a x2 assumption and bounded by the Cernov bound. A fundamental design problem involves the system bandwidth analogously, in a special case, as in diversity communication systems; a solution is given based on the Cernov bound. A set of summary design curves is given and exemplified by a satellite SAR system design. Also discussed is the measurement of reflectivity spectral density amplitude with imaging sidelooking (synthetic or ?brute-force?) radars and the maximum likelihood estimator's accuracy and realization with a coherent optical system. It is also shown that a CW modulation is useable if the random reflectivity is, effectively, isotropic. Finally, the reflectivity density spectral density amplitude, when constant over the spatial bandpass of the measuring system, is related to the scattering cross-section density commonly measured.     

Computation of aircraft geometric height under radar surveillance

A radar system for geometric height estimation of civil aircraft is described. The system consists of one standard or mode S secondary surveillance radar (SSR) and one omnidirectional antenna sited away from SSR under an airplane. The geometric height is derived by trilateration. Systematic errors are compensated for by deriving the profile of the effect on height measurements of the bias in range measurements. A curve-fitting technique is then used, which estimates both the geometric height and any non-zero systematic errors     

Radar Tracking of Low-Altitude Targets

The antenna elevation control signal and the associated staticequilibrium equations are analyzed for the case of tracking of lowaltitude targets for both monopulse and conical-scanning radar. Three possible equilibrium positions of the radar antenna under static operating conditions are ascertained. The static solutions suggest certain dynamic solutions that are likely to arise under practical conditions. The extreme values of the pointing error are shown in graphical form.     

Spectrum Distortion Due to Frequency Instabilities in a Two-Way Coherent Doppler Radar

The power spectral density of the intermediate frequency signal in a coherent Doppler navigation radar is derived. The effects of antenna parameters, periodic frequency instabilities, signal two-way transit time, and transmitter frequency modulation noise are considered Several examples based on the measured frequency modulation noise of a solid-state source transmitter are presented. The results indicate the degree of loss in signal-to-noise ratio, and spectrum broadening due to an increase in signal transit time and/or frequency modulation noise.     

Ultrawideband microwave-radar conceptual design

This paper outlines the special considerations that characterize the design of an UWB radar for the detection of low-altitude missiles over the sea. It discusses the factors which enter into the choice of frequency, and the selection of the transmitter, antenna, and receiver. Reviewed are signal processing issues concerning detection of UWB signals in noise and clutter, nondoppler MTI based on the pulse-to-pulse change in range due to target motion, measurement of target height based on multipath time delay, and target recognition. As the investigation progressed, the authors became disappointed with the available UWB technology, but encouraged about the potential advantages of UWB for this application. The chief limitation of UWB radar that must be overcome before applications are viable is its poor electromagnetic compatibility (EMC)     

一种基于u检验的空海目标分类方法

阐述了对于机载雷达,测高精度不高,特别是对远距离目标的测高精度更差,因而利用机载雷达提供的高度信息进行空海目标分类存在很大的不确定性。为了能有效地利用目标高度信息进行空海目标分类,把空海目标分类问题看成是一个u检验问题。首先,给出了用于空海目标分类的判别函数;然后,给出了一种决策规则,并推导出决策门限的计算公式和空中目标误判为海面目标的概率的计算公式;最后,通过仿真表明该算法的简易性和有效性。     

A Modified Monopulse Technique for Radar Tracking with Low-Angle Multipath

In this paper a new monopluse technique for reducing radar multipath angle-tracking errors is proposed. The solution is achieved by using two monopulse antennas at different heights. The available signals allow one to control the antenna-height diversity so that the elevation angle control signal is not affected by reflected-wave components. The size of the antenna system may be reduced by properly using phase shifters. A possible configuration of such a system is considered and some practical data on the antenna-height diversity are discussed.     

一种机载雷达机械扫描空域稳定改进算法

机载雷达在载机机动时,为保证天线视线空域指向范围不变,采用空域稳定的算法。当给定的方位和俯仰指令不在同一坐标系时,采用传统的算法会使得实际的空域与理想空域在载机机动幅度较大时有很大误差。文章提出一种算法,使得雷达扫描中心精度与期望值十分接近。同时,对于坐标转换中方位和俯仰的指令间覃相影响引起的俯仰指向精度降低问题,提出...     

Design of a space-based radar signal processor

Space-based radar (SBR) is capable of providing flexible wide-area coverage of air, land, and sea targets. Numerous studies have been carried out in the United States and Canada in recent years to investigate different concepts for SBR. The design of a suitable radar signal processor (RSP) is challenging due to the effects caused by the moving platform on target integration and clutter spectral spread. A candidate RSP is described that uses a corporate fed array (CFA) antenna as its primary radar sensor. The algorithmic definitions of the signal processing functions are provided; the relationships between these functions and the reasons for their location in the signal processing chain are also discussed. In addition, techniques for reducing the computational requirements are also presented     

海面低飞情况下机载航管二次雷达覆盖研究

二次雷达较之一次雷达有许多优点，使其在军用和民用领域得到广泛应用。但当装有航管二次雷达的飞机在海面低飞时，会出现常见的多径效应现象。文章详细分析了飞机机体和海面对航管二次雷达方向图的影响，并利用HFSS软件对飞机在海面低飞时航管二次雷达方向图进行仿真。结果表明，海面影响航管二次雷达的方向图并导致根据其分叉变形，根据平面对天线方向图的影响及其计算公式，对不同飞行高度的方向图进行了计算，得出了在海面低飞时的最佳飞行高度。     

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.     

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

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.     

Synthetic Aperture Radar

The general theory of side-looking synthetic aperture radar systems is developed. A simple circuit-theory model is developed; the geometry of the system determines the nature of the prefilter and the receiver (or processor) is the postfilter. The complex distributed reflectivity density appears as the input, and receiver noise is first considered as the interference which limits performance. Analysis and optimization are carried out for three performance criteria (resolution, signal-to-noise ratio, and least squares estimation of the target field). The optimum synthetic aperture length is derived in terms of the noise level and average transmitted power. Range-Doppler ambiguity limitations and optical processing are discussed briefly. The synthetic aperture concept for rotating target fields is described. It is observed that, for a physical aperture, a side-looking radar, and a rotating target field, the azimuth resolution is ?/? where ? is the change in aspect angle over which the target field is viewed, The effects of phase errors on azimuth resolution are derived in terms of the power density spectrum of the derivative of the phase errors and the performance in the absence of phase errors.     

一种基于协方差矩阵加权的阵元误差补偿STAP处理

机载多通道阵列雷达天线在工程实践中不可避免地存在各类阵元误差,所产生的通道失配问题会对空时二维自适应处理的性能造成大的影响。对存在阵元误差时的阵列信号模型进行了分析,提出了一种基于协方差矩阵加权（CMT）的阵元误差补偿空时自适应处理（STAP）方法,在工程应用中该加权矩阵可通过地面天线定标及校飞过程确定,通过对总干扰协方差矩阵估计的加权预处理,可将实际阵元误差对STAP性能的影响控制在测量误差的影响范围,最后通过仿真验证了算法的有效性。     

Multipath Fluctuation Effects in Track-While-Scan Radar

A theoretical model of diffuse multipath reflections from rough surfaces is applied to the prediction of multipath power distribu tions in radar coordinates: elevation angle, time delay, and Dop pler frequency. These distributions are used to predict radar tracking errors in elevation angle, for both monopulse and scan ning antenna systems, and typical results are presented. These show a small increase in tracking error for scanning systems, on radially approaching targets, caused by sensitivity of these trackers to amplitude scintillation of the composite direct-plus multipath signal. Effects of knife-edge diffraction and of vegetation ion are briefly considered.     

On-orbit calibration of satellite antenna-pointing errors

A pragmatic approach is presented to the on-orbit calibration of the spaceborne gimbaled parabolic reflector antennas to enhance their pointing and tracking accuracies in the presence of unknown structural deformations and other errors. The technique described is based on the second-order extended Kalman filter. Except for some knowledge of Kalman filtering, the work is self-contained and tutorial in character, developing necessary error models and deriving most pertinent equations from first principles. Preliminary simulations, from which covariance analysis results have been obtained, indicate a 66% improvement in the accuracy of the antenna pointing angles     

The Segmented Aperture Synthetic Aperture Radar (SASAR)

A new concept in synthetic aperture radar, called SASAR, which uses a segmented aperture, is described. Use of the segmented aperture allows appreciable extra receiving antenna gain to be realized. Each subarray of the receive antenna is equal in length to the transmit antenna; the system performance is increased approximately by a factor equal to the number of subarrays. To allow array combination of the subarray signal outputs requires a phase-shift factor (varying with azimuth) to be applied to each subarray signal. A digital implementation of this preprocessor is sketched out; it uses a push-down storage stack to store the range histories for a synthetic aperture from each subarray. Appropriate phase shifts are added to the stacks and a sum of stack values then provides the combined output range history sequence. Possibilities of using analog delay lines for preprocessing are also discussed. Pattern errors due to subarray size and receive array near field are examined and constraints are given.     

Design and calibration of the SeaWinds Scatterometer

The SeaWinds Scatterometer is a Ku-band Earth orbiting remote sensing radar. It has a 1 m dish antenna shared by two beams with respective nadir look angles of 40 and 46 deg, scanning azimuthally to provide greater than 90% daily coverage of the Earth at an altitude of 800 km. The first sensor was launched in 1999 and produces sea surface wind field to 2 m/s accuracy at 25 km resolution. The design and calibration of the SeaWinds radar is described here.