雷达接收机内部噪声特性研究

给出了一种雷达接收机抗内部噪声干扰的数学模型,研究结果适用于一般电子设备的热噪声问题,具有普遍的指导意义及实用价值。     

Tracking Performance of a Monopulse Radar in the Presence of Multiple Targets

The equations derived by A. J. Rainal for the probability density function of the angle error output of a monopulse radar excited by a Gaussian signal and Gaussian thermal noise are generalized to include the presence of multiple targets. The examples given demonstrate the radar's behavior for various combinations of target and noise parameters.     

雷达抗干扰能力度量方法的研究

 本文论述了度量雷达抗干扰能力的方法,提出了一组通用的度量公式。这些公式的基本部分是由雷达的主要技术参数组成。代表雷达的潜在抗干扰能力。公式的补充部分是由雷达各种抗干扰技术措施的指标所组成,代表这些抗干扰措施的质量水平。用这组公式可以计算出雷达抗消极干扰能力、抗积极干扰能力与综合抗干扰能力的表征数值。本文给出了计算举例,讨论了计算结果在雷达系统分析与总体设计中的应用。     

对空情报雷达的费用-效能分析

 本文目的是研究对空情报雷达的全寿命费用与效能之定量评价。首先分析该类雷达全寿命费用的组成。其次着重研究和推导了该类雷达性能和效能的数学表达式。最后统计和计算了多种雷达的费用、性能、效能与费效比的数值,绘制了发展曲线,讨论了这些计算和曲线在雷达总体工程中的应用。     

Kinetic cyclotron and synchrotron maser instabilities: Radio emission processes by direct amplification of radiation

This article reviews the theory of the kinetic (cyclotron an synchroton) maser instabilities. The subject has been extensively developed in recent years by many authors, who have been incited by the research of the auroral kilometric radiation and other applications. The maser mechanism is appealing because it is simple and efficient, and can lead to direct amplification of radiation. Two types of electron distribution functions have been investigated so far. These are the loss-cone and hollow-beam distributions which may exist pervasively in many regions within and beyond the solar system. It is likely that the maser instabilities can have many potentially important applications to numerous radio emission processes observed in astrophysical research.     

基于Log—Sigmoid型径向基神经网络的雷达辐射源识别

提出基于一种新的鲁棒性径向基 (RBF)神经网络的雷达辐射源识别方法。此网络应用Log -Sigmoid函数作为基函数 ,避免了学习过程中的不稳定状态 ,并且比传统的RBF有更好的学习性能和函数逼近能力。并介绍一种新的归一化函数 ,通过归一化函数把不同类型 ,不同量纲的原始评估数值转换到 [- 1,1]区间 ,该效用函数较好地体现了“奖优罚劣”的原则 ,同时又更有利于神经网络的训练。仿真实验证明了该方法的优越性。     

Fiber-optic radar calibration

A simple fiber-optic radar calibration target is described. Its operation is based on a wideband fiber, a laser transmitter that is directly modulated by the down-converted radar signal and an optical diode receiver recovering said signal. Further up-conversion having a common local oscillator with the first mixer ensures fidelity of the calibration return. Measured useful bandwidth exceeds 200 MHz and practically any radar RF frequency can be handled when suitable mixers are employed. Amplifiers can be added to the down-converted path as desired to compensate for the fiber loss. Modulation and LO sweep provide easy ways of introducing artificial fluctuations and Doppler frequencies. Particularly pulsed radars are readily tested with the proposed scheme as no restrictions are posed by the radar's TR-switch delays.     

Environment and Radar Operation Simulator

The environment and radar operation simulator (EROS) is a hardware system whose function is to produce realistic synthetic radar backscatter, incorporating both target and clutter. The simulator is electrically connected to a subject radar and responds in real time to the radar's antenna scan angle by producing the correct composite video signal.     

Characterization of NAVSTAR GPS and GLONASS on-board clocks

Investigation into navigation satellite on board clock frequency references and performance are reported. The focus is on the stability of the clocks aboard the NAVSTAR GPS (Global Positioning System) and GLONASS satellites as well as those used by their respective maser control stations and associated time scales. Allan-variance techniques have been applied to determine the long-term time-domain behavior of satellite clocks in an attempt to identify different regions of power spectral density. Coupled with analysis of relative-frequency drift over a period of many weeks, this behavior allows the type of satellite onboard standard to be tentatively identified. The known nature of the GPS clocks has shown that the different types of clocks aboard the satellites (crystal, rubidium, and cesium) are distinguishable given a sufficient sample time. The same approach has been applied to the GLONASS satellites, and a comparison of the results obtained from GPS has allowed conjecture on the type of clock used by the GLONASS satellites. It appears that GLONASS has used clocks of the quality of rubidium atomic oscillators since at least 1986, and that the quality and performance of onboard standards have increased steadily with time. Some current satellites perform well enough in terms of frequency drift, flicker FM noise floor, and long-term stability to compare favorably with the cesium beam standards carried on NAVSTAR GPS satellites launched in 1983-84     

An approach to radiated testing of installed airborne Doppler radarwith weather/windshear detection capability

Numerous documents were reviewed to verify radar parameters needed to analyze and present the tester concept described herein. The weather and windshear models defined use the identical criteria established for the Doppler radar in terms of F-factor. The basic concept of the tester is to transmit coherent simulated radar returns in response to the airborne radar's transmission while mounted on a tripod in the far field of the radar when parked on the ramp. The varying amplitude of the received radar pulses are analyzed and put into memory as the tester antenna is illuminated by the scanning main beam and side lobes of the radar's antenna patterns. The tester controls the power of its outputted simulated radar returns in inverse relation to the power of the received radar pulses. These simulated radar returns, outputted into the main beam and/or side lobes of the scanning radar antenna, are interpreted by the radar system as received in the main lobe. The tester transmissions, incorporating microburst, storm and gust front models, previously defined, can thereby test the aircraft radar system performance in various hazard environments. The tester is designed to: verify operational performance of the radar; demonstrate installed radar performance; verify crew reports and minimize radar or LRU's removal for maintenance; test before and after a repair; and verify radome effects on radar performance     

Threshold Control for Automatic Detection in Radar Systems

In automatic detection in radar systems an estimate of background clutter power is used to set the detection threshold. Usually detection cells surrounding the cell under test for the presence of a target are used to estimate the clutter power. In the research reported herein, the target location is taken to be uncertain and thus returns from a target could corrupt this clutter power estimate. It is shown how the threshold should be varied to compensate for the resulting degradation in detection performance. The threshold control procedure is based on a priori information about target location that could be supplied by the radar's tracking system. In addition, a simple procedure for calculating detection and false alarm probabilities for Swerling II target models is presented.     

Resolution and synthetic aperture characterization of sparse radar arrays

The concept of radar satellite constellations, or clusters, for synthetic aperture radar (SAR), moving target indicator (MTI), and other radar modes has been proposed and is currently under research. These constellations form an array that is sparsely populated and irregularly spaced; therefore, traditional matched filtering is inadequate for dealing with the constellation's radiation pattern. To aid in the design, analysis, and signal processing of radar satellite constellations and sparse arrays in general, the characterization of the resolution and ambiguity functions of such systems is investigated. We project the radar's received phase history versus five sensor parameters: time, frequency, and three-dimensional position, into a phase history in terms of two eigensensors that can be interpreted as the dimensions of a two-dimensional synthetic aperture. Then, the synthetic aperture expression is used to derive resolution and the ambiguity function. Simulations are presented to verify the theory.     

Plasma-maser effects in plasma astrophysics

The role of a new mode coupling effect (plasma-maser) in space plasma physics is reviewed. The new maser effect, the idea that the resonant electrons with the low-frequency mode can amplify the high-frequency mode, does not require population inversion of electrons. The generation mechanisms of ULF modulated ELF emissions, auroral kilometric radiation, chorus related electrostatic bursts, whistler mode in the solar wind, and type III solar radio bursts are studied based on plasma-maser effect. The forced plasma-maser interaction model reduces to a conservative Lotka-Volterra system. A chaotic behavior of the forced Lotka-Volterra system is obtained. The new mode coupling process has potential importance in attempting to interpret numerous astrophysical radio phenomena.     

VLBI Space Observatory Programme (VSOP) satellite

The Institute of Space and Astronautical Science (ISAS), Japan, is developing a satellite, named MUSES-B, for VLBI (very long baseline interferometry) observations from space. The science observation program using MUSES-B is called the VLBI Space Observatory Programme (VSOP). The satellite is formed as an orbiting radiotelescope with a parabolic antenna of 8 meters diameter. Fine-resolution and high-quality imaging of active galactic nuclei and quasars, and observations of maser sources, are the main science objectives. The satellite will be launched in summer 1996. The satellite operation and science observations will be performed in collaboration with NASA and ground radio observatories around the world     

Comments on `SCR-20 Radar Development' and `The SCR-270 in Japan'by Viewager et al

To add to the history of the SCR-270 radar's development (see Viewager et al., vol.3, no.12, p.3-6, 1988 and F. Voltaggio, ibid., vol.3, no.12, p.7-14, 1988) the commenter presents personal recollections regarding the modifications made to several SCR-270 radar sets operating in Hawaii just before the start of World War II     

SEVERAL PROBLEMS IN DESIGNING DBS SYSTEMS FOR AIRBORNE PULSE DOPPLER RADAR

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Analysis of a Signal Processor for an Antenna Array

A signal processor that provides ratio-squared predetection combining, has been investigated for application in an adaptive antenna array. The analysis and experimental data presented here pertain to the signal processing gain when the antenna array is illuminated by a coherent signal source and a partially coherent noise source. For a noise source which is coherent, the processing gain depends on relative strength of the signal and noise, relative directions of arrival, and the usual "array factor." The array exhibits capturing effects much as in an FM receiver. The effective antenna pattern is a superposition of two beams of different magnitudes, one directed to the signal source and the other to the noise source. When the noise is partially coherent, the behavior of the signal processor is quite complex. Analytical prediction and experimental simulation measurement on a four-channel system indicate that the partially coherent noise may be regarded as the source of an incoherent noise component plus a coherent noise component with the magnitude of the latter determined by the coherence coefficient for the noise source.     

Nonlinear target enhancement for the hostile nuclear environment

A necessary requirement of a strategic defence system is the detection of incoming nuclear warheads in an environment that may include nuclear detonations of undetected or missed target warheads. A computer model which simulates incoming warheads as distant endoatmospheric targets is described. A model of the electromagnetic noise expected in the nuclear environment is developed. Predicted atmospheric effects are also included. The ability of nonlinear image enhancement algorithms to their ability to suppress the noise and atmospheric effects of the nuclear environment is examined. These algorithms are then tested, using the combined target and noise models, and evaluated in terms of noise removal and their ability to resolve closely spaced targets     

声学引导风洞高效低噪声风扇设计

运用任意涡风扇设计方法,进行声学引导风洞高效低噪声风扇设计。在设计过程中,通过调整叶片径向旋转系数分布优化叶片出口速度分布,通过合理匹配转子、定子数目及定子后掠角度来改善动静叶的干涉噪声。气动及声学性能试验表明,高效低噪声风扇设计点气动效率达到83.9%,相比引导风洞原风扇效率的73%有了明显的提高;高效低噪声风扇入口及出口噪声分别比原风扇入口及出口噪声低3dB（A）和2dB（A）。试验结果成功验证了任意涡设计方法在风扇气动及声学性能上的优越性。