MTI Processing and Weibull-Distributed Ground Clutter

It is shown that the Weibull-distributed ground clutter obeys a Weibull distribution after processing by the double canceler moving target indicator (MTI).     

Clutter Residues of a Coherent MTI Radar Receiver

In moving target indicator radar receivers a saturation is always present in the IF stages in order to compress the dynamic range of large clutter inputs. This nonlinearity greatly affects the performances of the cancelling circuits, because of the spreading of the spectra. A quantitative analysis of this effect has been conducted, with an analytical expression chosen for the limitation characteristic. A high degradation of both single-and double-canceller improvement factors has been obtained. Losses of 20 dB for the double canceller are not uncommon. Clutter residue levels at the receiver output have also been computed in order to see how the performance compares with ideal constant false alarm rate behavior.     

Design and Evaluation of an Adaptive MTI Filter

The design and evaluation of an adaptive moving target indicator (MTI) filter, the adaptive canceler for extended clutter (ACEC) is dealt with, taking into consideration adaptivity to clutter mean Doppler frequency. This consideration is one of the most important operational requirements in adaptive MTI's and permits a relatively simple hardware implementation as compared to more general optimization and adaptivity criteria (briefly described). The ACEC's algorithm compensates in real time for the clutter mean Doppler frequency. Performances have been obtained by digital computer simulation in various operational conditions.     

The Effect of Spectral Shape on Clutter Standard Deviation

Many radar systems now employ wideband waveforms and noncoherent averaging techniques to reduce the scintillation of the backscatter from ground clutter. The purpose of this paper is to quantify the effects of the wideband spectral shape on the clutter standard deviation after noncoherent averaging of the received signal. Relationships are developed which quantify the clutter standard deviation for any spectral shape and any ratio of transmitted band-width to processed bandwidth.     

Effect of timing jitter on performance of MTI filters

The effect of transmitting timing jitter and sampling jitter on a multipulse clutter cancellation system is analyzed, and explicit expressions are obtained for the net increase in the residue clutter power due to timing jitter. The increase in mean-square error is found to be proportional to the jitter variance, with the two jitters contributing almost equally. The system analyzed can have either a recursive or nonrecursive MTI filter, and the latter includes the familiar two- and three-pulse canceller as special cases. The increase in residue clutter power for a three-pulse canceller is about 4.8 dB worse than that for a two-pulse canceller     

The Susceptivity of MTI Systems to White Noise

The performance of various coherent MTI systems in the presence of white noise is investigated. The single-pulse signal-to-noise ratios at the output of the filters are presented for the case of large system bandwidth. Generalized results, calculated as a function of the system's bandwidth, are given. Finally, those results are compared to the optimum signal-to-noise acheivable by a matched filter.     

Effect of Radar Amplitude and Phase Weighting Errors on Clutter Rejection by Burst Waveforms

This correspondence derives simple expressions for the ambiguity function X and the Q function of uniformly spaced burst waveforms that are subject to independent random errors in the transmitter and receiver pulse phase and amplitude weightings. The expressions are similar to those in [1], but have been put in more simplified form, and are valid for more general sources of error.     

铆模锥度及深度对铆钉成形质量影响

本文采用ABAQUS建立了有限元分析模型,分析了40°、50°、60°3种铆模角度和1.5mm、1.8mm两种铆模深度对铆钉成形的影响规律。通过试验分析表明,铆模锥度及深度对铆钉镦头的成形影响显著,适当增大铆模锥角同时增大铆模深度至1.8mm有利于消除铆钉镦头的卷边,提高铆接质量。     

喷嘴和旋流器数目对短环形燃烧室燃烧性能的影响

通过改变燃烧室头部喷嘴、旋流器的数目和位置,对短环形流燃烧室内有较强回流的湍流旋流流动进行了模拟。结果表明:在燃油和空气总流量不变的情况下,改变喷嘴数目对燃烧室出口平均温度、平均速度影响不大,但是,对出口温度分布、燃烧室内空气流场有较大影响。     

The Generation of Correlated Weibull Clutter for Signal Detection Problems

A method is discussed for generating Weibull vectors with a desired correlation matrix and specified parameters. Such vectors may represent samples of a correlated clutter signal. The presented method makes use of a suitable nonlinear transformation of random Gaussian vectors with correlated components. Computational aspects of the method are also discussed.     

Suboptimal Simulation and Suppression of Clutter Signals

Two digital filters are presented, which are suited for generating (Correlation) or suppressing (decorrelation) by approximation time-discrete signals with preset autocorrelation function from white noise. The advantage of these suboptimal filters is that the determination of their coefficients is very simple. For this reason the filters are weil suited for generating or suppresing signals with rapidly varying statistical parameters. One application possibility is the simulation and the adaptive suppression of clutter signals in surveillance radar systems.     

模糊C均值算法在机载PD雷达杂波跟踪中的应用

介绍一种适用于机载PD雷达的杂波跟踪技术,结合机载PD雷达杂波分布特征和模糊C均值算法的特点,将模糊C均值算法用于杂波跟踪,给出了相应的算法流程,并提出了一种确定初始模糊隶属度的方法,经仿真数据验证,取得了满意的结果。     

Correlated Clutter and Resultant Properties of Binary Signals

A simple Markov process model of binary, digitized radar clutter returns is assumed. Probability distributions for the number of hits in n observations are developed for small n with a binary parameter describing the process derived for Rayleigh distributed clutter. Tables of distributions are included, along with an example to show the effects of correlation on the false-alarm probabilities of a sliding-window detector.     

Comments on: "Design of MTI Radar on the Basis of Detection Probability"

The main comment of the above paper [1] is that radar integration after MTI processing is not taken into account. For this reason, its numerical results (and curves) show processing losses much higher than practical values. The latter can be obtained in a relatively easy way by means of a computer simulation of the entire signal processor.     

构件打磨深度对疲劳寿命的影响

按照飞机结构修理手册的规定,腐蚀损伤的允许打磨深度不超过构件厚度的10%。疲劳寿命计算和试验结果表明,从疲劳强度角度考虑,如果损伤部位修理不能利用原紧固件孔安装紧固件,并且又只能采用非对称铆接修理,则打磨深度在总厚度的10%～20%时,较合理的修理仍是通过打磨清除腐蚀,然后恢复涂层。     

复合材料孔隙率超声衰减法检测技术研究进展及应用

介绍了近年来复合材料孔隙率超声检测研究现状和国内外采用超声衰减法测量孔隙率的理论模型、检测结果,并对各种模型进行对比和分析;论述了国内外各航空制造商的孔隙率超声衰减法检测的工程检测方法,对复合材料孔隙率超声衰减法检测技术的发展及应用提出了研究方向.     

The Kalman Filter Applied to Aerospace and Electronic Systems

The evolution of the application of the Kalman filter in the aerospace arena is traced. The major programs that were the driving forces for the filter's acceptance are noted, as are the specific threads of activity for refining and enhancing the initial contribution. These efforts brought the fundamental ideas presented by Kalman to the point where actual application was possible. Clearly the concepts of the Kalman filter are now "mature." This is also noted and substantiated.     

Probability of Detecting a Fluctuating Target Immersed in Both Noise and Clutter

The probability of detecting either a Swerling 1 or Swerling 2 target immersed in both Rayleigh-distributed noise and log-normally distributed clutter is calculated. Results are presented which demonstrate the effect of noise-to-clutter ratio, signal-to-noise ratio, and number of pulses integrated on the detection statistics.