Acquisition Time of Tracking Loops Operating in the Frequency-Search Mode

This paper presents a theory for computing the signal acquisition time of a second-order tracing system operating in the frequency-search mode. In particular, a closed-form expression is obtained which relates the acquisition time to the relevant system parameters, to the initial loop detuning, and to the slope of the ramp that sweeps the voltage-controlled oscillator. Although the theory is only approximate and the resulting formula is exact only in the limit when the initial loop detuning ?F goes to infinity, it has been found that it gives quite accurate results as soon as ?F is some times greater than the equivalent noise bandwidth of the loop.     

Acquisition Time of Second-Order Aided PLL

The analysis of a second-order tracking loop operating in the frequency-search mode is carried out by the quasi-stationary approach. An arbitrary phase detector characteristic is assumed and perfect or imperfect integrating filters are considered. The theory leads to a closed-form expression of the acquisition time versus the relevant system parameters, the initial detuning, and the search rate. The limitations of this analysis concern the absence of noise and the hypothesis of large initial detuning.     

静电驱动悬臂梁式微开关的动态特性分析

通过建立静电驱动悬臂梁式微开关的非线性动力学简化模型,利用数值方法求解出系统的动态响应特性,得到了动态吸合电压和开关吸合时间的关系,并详细分析了其动态响应中的非线性现象以及动态特性和静态特性的不同。计算结果表明,动态吸合电压并不是唯一的;随着动态吸合电压的增大,吸合时间逐渐变小;微悬臂梁的动态响应周期随着驱动电压的增大而增大;动态临界电压低于静态临界电压,这些动态特性与静态特性有着明显的不同。     

Phase Locked Loop Acquisition for a Noisy FM Signal

A method based upon the quasi-linearization technique of evaluating the pull-in characteristics of a phase locked loop for an angle modulated signal corrupted with Gaussian noise is presented. Experimental results along with formulas for calculating the locking range and locking time are also presented and they are in good agreement with the theoretical results. Some new findings regarding the dependence of the locking range and locking time on the modulating frequency are also incorporated.     

Pull-In Behavior of Third-Order Generalized Phase-Locked Loops

This paper analyzes third-order phase-locked loops with an arbitrary phase-detector characteristic and imperfect integration by the quasi-stationary approach with a suitable linearization of the non-linear differential equation deseribing the loop behavior; ideal integration is also considered. The main feature of this technique is the use of an easy mathematical approach which allows a direct physical insight into acquisition behavior and the development of simple expressions for the time and pull-in range.     

Graphical Analysis of a Digital Phase-Locked Loop

Under the assumption of negligible quantization error effect and no noise, a nonuniform sampling first-order digital phase-locked loop (DPLL) is analyzed by a graphical method which displays limit cycles and the cycle slipping phenomenon. The analysis suggests an upper bound to the model gain and, consequently, to the pull-in range. Moreover, this method enables one to obtain a closed-form expression of the acquisition time, accurate enough for the cases of practical interest.     

Terminal Guidance for Impact Attitude Angle Constrained Flight Trajectories

The design of a suboptimal terminal guidance system for reentry vehicles with a constraint on the body attitude angle at impact is studied. Permissible range of the miss distance and the body attitude angle at impact is specified. The problem is formulated as a linear quadratic control problem. The Riccati equation is derived to provide time-varying feedback gains. The desired scheme is suboptimal. The region of initial states for which the system meets the specifications becomes smaller as the initial height of the reentry vehicle at initial time is decreased.     

LBTR线性系统结构图法数字仿真

本文提出了一种新的系统结构图数字仿真的方法。由于采用分子和分母都是二阶的典型环节,因而通用性强、使用更方便。文中推导了系统结构图和状态方程之间变换的数学表达式。所设计的计算矩阵指数的子程序保证了系统仿真精度不受计算步长的限制,从而大大提高了计算效率。本软件适用于多输入多输出系统,并备有多种类型的输入函数,还可以在任意环节加入初始条件,所以很适合于工程使用。     

To a Matter of Increasing the Spectral Efficiency of Phase Radio-Technical Data Transmission Systems Operating under Strong Intersymbol Interference

This paper analyzes the possibility of increasing the spectral efficiency of phase radio-technical data transmission systems that operate under conditions of mutual interference of symbols when “transparency windows” are used. The conditions for emergency of “transparency windows” are defined, recommendations for their application with the purpose of increasing the spectral efficiency of communication systems being considered are presented. Changes in time characteristics of “transparency windows” are analyzed (their lengths over the range of channel symbol time duration) depending on the frequency detuning.     

Analytical and Experimental Results for Maximizing the Pull-in Range of Product Correlators

Product correlators are being developed and implemented as a means of improving the guidance capability of tactical missiles. Analytical and experimental results are presented for maximizing the pull-in range of product area correlators via investigation of the discriminator curve of the correlator. The maps used in the correlation are assumed to be sample functions from two-dimensional, zero-mean, stationary Gaussian random processes. To obtain closed-form results, the additional assumption of a Gaussian correlation function is made. These analyses and results should be applicable to a wide range of correlation systems. Implications of these results as they pertain to missile guidance are discussed.     

压气机效率的正确变比热计算

随着实际压气机压机压比不断增高，按定比热等熵指数ｋ＝１．４的算法，误差越来越大。文中按照给定或实验测定压比，初温，终温的命题，给出计算效率的正确变化比热算法，并控压比５至３０分档作出算例，同时检验出，如简单地按初温冬温求ｋ算效率误差很大，几乎与定比热法同一量级。工程中常年用定比热已久，如何给出简便校正方法。尚待研究。     

狭缝内乙烯/氧气预混气体爆轰几何极限的实验

为研究狭缝内爆轰波传播极限,实验得到了不同初始压力(0.004~0.04MPa)下化学恰当比的乙烯/氧气预混气体在狭缝高度为1.0~4.0mm狭缝内的爆轰性能.采用烟膜板记录爆轰波运行轨迹,高速摄影捕捉火焰面.结果表明:狭缝高度越小,爆轰极限对应的临界初始压力越高.对于近极限条件内不稳定爆轰传播模式,包括"结巴"爆轰和驰振爆轰,其对应的初始压力范围随着狭缝高度的降低而变宽.考虑初始和边界条件,将水力直径与胞格宽度之比作为合理的爆轰敏感性参数描述预混气体爆轰特性,得出在不同狭缝通道内爆轰极限范围为,即该比值在0.326~0.403之间.      

液氧甲烷发动机点火冲击特性研究

为研究液氧甲烷发动机燃烧室点火冲击特性及影响因素,根据爆轰波产生的机理,建立了甲烷推进剂液相蒸发数学模型,采用C-J（Chapman-Jouguet）爆轰理论,计算和分析了不同混合比、初温及初压对爆轰参数的影响规律。结果表明,爆轰波的强度与初压、初温及混合比密切相关。初压越高,初温越低,越接近化学当量混合比时,爆轰压比、温度比和爆轰速度越大;减小点火时刻推进剂积存量,增强燃烧装置点火能力,可降低爆轰波强度,减少点火瞬态冲击。     

探测点序列的最优化与简化计算方法

在搜索状态建模和求解一阶搜索状态方程的特征迹线解的基础上,建立了对随机运动进行离散时间探测的发现概率最优控制模型,结合动态规划原理给出一种最优探测点序列的逼近算法,并给出了短时计算的算法简化形式。在满足一阶搜索状态方程的随机恒速目标条件以及有限指数探测函数条件下,将给出的算法及其简化形式应用到算例。算例表明,当随机恒速运动目标初始位置和速度均服从圆正态分布时,该算法及其简化形式均能够由任意给定的初始探测点序列优化收敛到满足精度要求的最优探测点序列。     

K-Band Tracking System for Domestic Satellite Communication System

System design and operational results of a tracking system for a K-band Earth station antenna with a diameter of 11.5 m are discussed. Monopulse tracking technique using higher order waveguide modes is utilized. An investigation was conducted to clarify the rainfall effect and the effect of oscillator phase noise on the tracking receiver. An autotrack system is to be manufactured on the basis of these studies. Experiments were performed using the medium capacity communications satellite. No cross coupling was seen in the pull-in patterns. Sufficiently good results were obtained in tracking accuracy: less than 0.005° (peak value) under normal conditions, and less than 0.01° under an average wind velocity of more than 20 m/s.     

Pull-In Performance of a Piecewise Linear Phase-Locked Loop

This is part of a study concerned with the analysis of phase-locked loops (PLL's). The broad objective throughout this work is to improve upon our general understanding in this important area. More particularly, ly, we are seeking quantitative results indicative of the pull-in behavior of PLL's. In the present paper, we point out some results in foreign publications and focus attention on a paper by Kapranov [1] which is devoted to the study of the pull-in frequency of second-order PLL's with a symmetric phase comparator. We apply the same approach and present results, in closed form, in the more general case where the phase comparator possesses an asymmetric triangular characteristic. Special cases of this phase comparator are the sawtooth and symmetric triangular comparators. It can also be viewed as an approximation to the Tanlock phase comparator. The RC filter case is treated.     

错频叶盘结构的概率模态局部化特性分析

以典型压气机叶盘结构为例,提出了实际错频结构的有限元建模方法,并考虑了随机加工误差的影响,定义了一种基于叶片应变能的模态局部化因子,基于ANSYS有限元和Monte Carlo数值计算,定量分析评价了错频叶盘结构固有频率和模态振型局部化的统计特性.研究表明,"错频失谐"会引起显著的振动局部化,叶盘错频设计中需要综合考虑结构的失谐振动局部化和气弹稳定性两方面.      

脉冲爆震发动机稳定工作性能的实验研究

为了对脉冲爆震发动机不同工作频率下稳定工作范围进行深入的研究,实验对汽油/空气可爆混气在不同工作频率、不同当量比下爆震发动机模型机的爆震压力和推力进行了测试,找出了不同频率下发动机稳定工作的最大和最小当量比。实验发现,当工作频率较低时发动机的稳定工作范围较宽,随着工作频率的增大,发动机的稳定工作范围逐渐变窄。在同一工作频率下,爆震发动机的平均推力随着当量比的增加是先增后降,但变化幅度很小,而混合比冲则是随着当量比的增加急剧下降。另外,在当量比一定的情况下,脉冲爆震发动机的平均推力随着工作频率的提高接近线性增加。     

Form-finding methods for deployable mesh reflector antennas

Deployable high-frequency mesh reflector antennas for future communications and obser- vations are required to obtain high gain and high directivity. In order to support these new missions, reflectors with high surface accuracy are widely required. The form-finding analysis of deployable mesh reflector antennas becomes more vital which aims to determine the initial surface profile formed by the equilibrium prestress distribution in cables to satisfy the surface accuracy requirement. In this paper, two form-finding methods for mesh reflector antennas, both of which include two steps, are pro- posed. The first step is to investigate the prestress design only for the cable net structure as the circum- ferential nodes connected to the supporting truss are assumed fixed. The second step is to optimize the prestress distribution of the boundary cables connected directly to the supporting truss considering the elastic deformation of the antenna structure. Some numerical examples are carried out and the simulation results demonstrate the proposed form-finding methods can warrant the deformed antenna reflector surface matches the one by design and the cable tension forces fall in a specified range.     

RP-3航空煤油模拟替代燃料的着火延迟特性

为了获得一种新的国产RP-3航空煤油模拟替代燃料的着火延迟特性,在化学激波管中完成了初始压力分别为0.1MPa与0.3MPa,当量比分别为0.5,1.0与1.5,着火温度为1000～1700K条件下该模拟替代燃料着火延迟时间的试验测试,分析了初始压力与当量比对该模拟替代燃料着火延迟时间的影响规律,并与相应工况条件下RP...