甚低频传播C层效应的观测与模式化研究

利用甚低频(VLF)传播相位的观测结果,证明了VLF传播C层效应的存在.基于C层效应产生原因,导出了包含C层效应的VLF传播相速时变函数和相位预测模型,并利用回归分析揭示了C层效应的日、季变化规律.     

船载ULF/VLF对潜通信系统可行性分析

为了实现水面舰艇与水下周围100 km或更远范围内潜艇之间的低频(ULF/VLF)通信,首先分析了ULF/VLF波在均匀半空间中的传播规律,然后结合ULF/VLF频段大气噪声谱密度、收发天线增益以及接收系统热噪声等数据,对ULF/VLF对潜通信的通信距离、入水深度、通信速率三个方面进行了具体地分析。     

极低频/超低频/甚低频宽带磁传感器技术研究

分析了极低频/超低频/甚低频(ELF/SLF/VLF)宽带磁传感器的工作原理,解决了磁天线低噪声、放大器低噪声、传感系数标校等关键技术问题,研制了ELF/SLF/VLF宽带磁传感器的样机并对其幅度特性、相位特性进行了测试,测试结果表明:设备性能达到了预期研究目标。     

甚低频在多模干涉区的场强起伏标准偏差估计

对于甚低频（VLF）电波而言,电离层随机不规则变化将影响传播路径上场强的稳定性,从而使得场强起伏在多模区特别是场强极小点附近较为明显。从VLF电波传播基理出发、研究分析了传播路径上电离层随机不规则变化对场强稳定性的影响,推导了多模干涉区、单模干涉区及场强极小点附近激励因子、哀减率和相速与场强起伏的关系,得出了传播路径上场强起伏标准偏差估计公式,并将此公式的理论计算结果与实测数据进行了对比。结果证明：此公式计算精度较高,能够自适应于多模干涉区、单模干涉区,此场强起伏标准偏差估计公式对VLF通信可靠性的研究具有重要意义。     

基于误差模型的结构光条纹周期数选择方法

目前相位测量轮廓术中条纹周期数的选择主要依靠定性方法,难以获得最优效果及系统的应用。本文提出了一种基于误差模型的条纹周期数定量选择方法。该方法首先根据相位测量轮廓术的误差来源建立相位误差模型,利用相位误差模型计算出最大相位误差。其次通过最大相位误差与相位展开算法的约束关系推导出条纹周期数约束方程。最后根据计算出的最大相位误差与条纹周期数约束方程的相互关系,估计出最优正弦条纹周期数。实验结果表明:使用由本文方法选择出的条纹周期数,得到标准平板的最佳平面拟合结果的标准差为003mm,相较于传统方法,降低了444。本文所提方法能够有效提高相位测量轮廓术的测量精度。     

计算电离层VLF波传输特性的时域有限差分算法

在星载甚低频( VLF)通信技术中,研究甚低频信号在电离层中的传输特性具有重要意义。现有的利用时域有限差分( FDTD)算法研究电离层传输特性大多基于高频脉冲信号,且传播模型相对粗略,计算存在一定误差。为此,建立了更为精确的电离层各向异性传播模型,对常规的FDTD算法引入变步长因子,并用该算法对VLF波在电离层中的场强衰减进行了数值计算,研究了昼夜变化及频率对其传输特性的影响。仿真结果与卫星实测数据对比表明：与常规的FDTD算法以及全波分析方法相比,引入变步长因子的FDTD算法精度更高;在VLF频段,降低频率有利于电磁波穿透电离层,且白天的衰减明显大于夜间;VLF波在射入电离层并穿透D层时衰减严重(30~40 dB),约为F1层中衰减的3倍。     

相位共轭反馈半导体激光器混沌动力学

本文研究了相位共轭反馈对半导体激光器的动力学行为的影响。结果表明，在弱反馈条件下，系统处于稳态;增加反馈量，系统由周期经周期三、周期四进入混沌。当相位共轭反馈量一定时，通过改变注入电流的大小，可以达到所期待的周期或混沌状态。     

少数周期光脉冲的初始载波包络相位的测量

提出了利用空气成丝产生的太赫兹波测量少数周期激光的初始载波包络相位（CEP）的方法。空气等离子体产生的太赫兹波形的演变可以用来探测传播中的少数周期激光的载波包络相位的变化。在少数周期强激光场，太赫兹波形反转的数目和反转位置都有规律地依赖于少数周期激光的载波包络相位。利用光电流模型的计算结果表明，在适中的能量范围内，对于所有的初始CEP，太赫兹波形反转点数目是两个或者一个，且在不同输入能量下，总是在初始CEP 为0.5 时，太赫兹波形的两个反转点变为一个反转点。这可以提供准确测量驱动激光场初始CEP 的方法。     

基于相位偏移的条纹投影相位误差补偿方法研究

相移条纹投影技术三维成像的过程中，受设备非线性效应影响存在相位误差。针对相位误差的周期特性，引入相位偏移算法，提出一种非线性相位误差全场补偿方法。利用非线性相位误差的偏移变化，结合多个包裹相位的相位值选取特定阈值，最后使用算法遍历全场相位信息获取理想相位。实验结果显示校正后的误差点数是校正前的2.52%,证实了方法的有效性，通过与其他方法进行数据对比分析，表明所提方法修正相位误差效果有所提高。     

几周期啁啾高斯脉冲的时域特性研究

研究了带有线性啁啾的几周期高斯脉冲的主要时域特性 ,分析了载波相位对啁啾脉冲的影响。结果表明啁啾在很大程度上增大了载波相位发挥作用所对应的脉宽范围 ,并且相位对啁啾脉冲的作用比对无啁啾的情况更加显著。     

VLF timing: Conventional and modern techniques including omega

VLF signals from 10 to 30 kHz play an important role in long-range time dissemination, communications, and navigation. A brief history of VLF transmissions is given with particular emphasis on the time dissemination capabilities of the Omega navigational system. Traditional methods are compared with modern capabilities. Traditional lead-edge time dissemination by VLF normally can provide an accuracy of a few milliseconds, although stabilized transmitters can permit an accuracy of better than 100 µs. Frequency comparisons to an accuracy of a few parts in 10¹¹per day typically are made with commercially available equipment. The present four-station Omega system will be expanded to an eight-station worldwide network in the near future. With implementation of this global network, carrier ambiguities can be resolved at a receiving station with a cesium frequency standard over intercontinental ranges; phase can be maintained to better than 3 µs and frequency to about 1 part in 10¹². Continuous maintenance of phase to better than 1 µs is indicated when using specialized techniques. Propagation aspects of VLF transmissions limit received accuracy; however, this is tempered by low attenuation of stable signals to long ranges.     

交错阵列甚低频信号产生方法研究

10 kHz量级甚低频电磁波信号具有较强的地物穿透能力,可用于地质勘探。由于其天线尺寸在10 km量级,其应用场合受到限制,研究基于适当尺寸高频雷达天线的甚低频电磁波信号产生方法具有重要意义。该文提出基于高频阵列天线产生甚低频信号的概念,利用阵列天线合成产生近光速远离运动雷达多普勒信号,实现信号频率的大幅降低。给出了发射波形、交错阵列设计和阵列参数选择方法。将周期脉冲串信号作为辐射单元信号,增大合成信号脉宽。利用阵列产生的脉宽展宽量填补脉冲信号的休止期,在目标区合成时间连续的甚低频信号。采用峰值旁瓣比(PSLR)、积分旁瓣比(ISLR)、阵列发射信号与合成信号的频谱对比评价合成低频信号的性能和发射信号的能量利用率。该文仿真了百米量级阵列100 MHz辐射单元信号在目标区合成10 kHz甚低频信号的情况:9行阵列构成交错阵列、辐射单元信号脉宽设置为0.115 μs时,合成信号频谱的峰值旁瓣比和积分旁瓣比分别为–13.34 dB和–9.44 dB, 10 kHz低频信号在合成信号中的能量占比为89.79%。该文分析了辐射单元间距误差、辐射单元信号时间、相位与幅度误差以及目标偏离预定位置的影响。仿真结果表明了该文方法的有效性。      

Applications of New Fuzzy Inference-Based Tracking Loops for Kinematic GPS Receiver

Carrier phase measurement is essential for high-accuracy measurement in kinematic global positioning system (GPS) applications. For GPS receiver design, a narrow noise bandwidth is desired to decrease phase jitter due to thermal noise. However, this bandwidth will deteriorate the capability of the tracking loop and result in cycle slipping. Based on bandwidth adjustment criteria, a novel intelligent GPS receiver is proposed for solving the carrier phase tracking problem in the presence of high dynamic environments. A phase error estimator is developed in the carrier loop to conduct the phase error signals; i.e., frequency and frequency ramp errors. Two kinds of fuzzy inference (FI)-based approaches, fuzzy logic control and adaptive neuro-fuzzy control methods, that are simple and have easy realization properties are designed to perform rapid and accurate control of the digital frequency phase-locked loop (FPLL). A new design procedure for kinematic GPS receiver development is also presented. The computer results show that the FI-based receivers achieve faster settling time and wider pull-in range than the conventional tracking loops while also preventing the occurrence of cycle slips.     

The Performance of Suppressed Carrier Receivers in a Pulsed RFI Environment

This paper investigates the tracking performance of a Costas loop in the presence of single and multiple in-band pulsed RFI signals and receiver additive noise. It is shown that the loop's tracking performance is very sensitive to the pulse durations of the RFI signals, as well as their repetition rates and peak powers relative to those of the desired signal. The presence of in-band RFI can affect the loop's tracking performance in basically three ways. 1) The loop tracks the composite phase of the RFI instead of the phase of the desired signal when the effective RFI power is greater than that of the signal. 2) When the effective RFI power is not sufficiently large to capture the loop, there still will exist static phase error biases which cause the loop to lock at a phase between that of the desired signal and the composite RFI. 3) There is an increase in the rms phase jitter over the nominal design. These latter two effects degrade the bit error probability performance of the receiver. More significantly, if the nominal loop bandwidth is not designed properly to account for the increase in jitter phenomenon, frequent cycle slipping may result.     

BPSK to ASK signal conversion using injection-locked oscillators-Part I: theory

This paper presents a new method and circuit for the conversion of binary phase-shift keying (BPSK) signals into amplitude shift keying signals. The basic principles of the conversion method are the superharmonic injection and locking of oscillator circuits, and interference phenomena. The first one is used to synchronize the oscillators, while the second is used to generate an amplitude interference pattern that reproduces the original phase modulation. When combined with an envelope detector, the proposed converter circuit allows the coherent demodulation of BPSK signals without need of any explicit carrier recovery system. The time response of the converter circuit to phase changes of the input signal, as well as the conversion limits, are discussed in detail.     

低频/甚低频电磁脉冲测量系统研究

为了准确地测量电磁脉冲（electromagnetic pulse,EMP）的波形,开展低频/甚低频（low-frequency/very low-frequency,LF/VLF）EMP的形成和传播机理研究,识别不同EMP的特征,并以此为依据来识别、确认雷电及核爆炸等现象,提出了一种高分辨率的EMP原始波形测量系统方案,同时针对LF/VLF这一较低的频段提出了一套有效的系统标校方法,实现了对EMP的连续、准确测量和快速有效判别,并能通过网络实时上传数据.系统采用正交环磁场天线和平板电容电场天线实现信号的接收,设计了低噪声高保真的信道调理电路和高速数据采集电路来实现信号的采集,利用高精度的授时模块为EMP信号标记时间戳,最后结合多点监测波形实现EMP定位估计.实测结果表明:该系统能够给出高分辨率、高精度的LF/VLF EMP波形;利用该系统组网可以实现远距离EMP源的定位,定位精度与目前近距离的定位手段相当.通过长期的运行,验证了该系统具有高可靠、低失真、判别准确、实时性强等特点.     

Convergence behavior of iterative phase synchronization and detection

Serially concatenated systems with rotational invariance (RI-SCS) can tolerate certain phase ambiguities and, therefore, for these systems coherent detection is robust even when cycle slipping, false-lock and hangup exist during phase synchronization. However, the convergence behavior of iterative phase synchronization and detection is still not well-understood. In this paper, we present a simplified phase model to analyze the convergence of iterative receivers with/without occurrence of phase rotations. Particularly, an oscillatory convergence behavior due to cycle slipping is explained by means of density evolution. Moreover, based on per-survivor processing (PSP) and single-estimator processing (SEP) techniques, a family of adaptive soft-input soft-output algorithms are employed to implement joint phase tracking and demodulation in the context of maximum a posteriori symbol detection. Both analytical and simulation results show that for RI-SCS the convergence performance of the SEP method is more robust than that of the PSP method when carrier phase has high and random dynamics.     

A Binary Quantized Digital Phase Locked Loop: A Graphical Analysis

A non-uniform sampling digital phase locked loop (DPLL), with a hard limiter as quantizer, is analyzed by a graphical method in the case of phase and frequency step inputs and no noise. The cycle slipping and the limit cycles phenomena are investigated. An upper-bound to the model gain and, consequently, to the pull-in range is obtained. Also a closed-form expression of acquisition time is derived. Moreover, using a random-walk model, the stationary phase error variance, the mean acquisition time and the mean first slip time have been evaluated. Some two channel configurations are proposed, which allow us to obtain a faster acquisition. Finally the problems relevant to the practical implementation of the loop are analyzed.     

一种多波长信号全光加密系统方案

为了能够同时对多波长信号进行加密操作,两路相干光信号进行直接干涉前,通过对其中一路光信号进行Pi相移,Pi相移后两路信号的干涉结果即为两信号异或(XOR)逻辑结果。基于此原理,提出一种应用于波分复用(WDM)系统,能够同时对多波长复用信号进行XOR加密的方案。方案通过直接电光调制得到不同波长相干光信号与光密钥,且通过相移单元同时对多波长光密钥进行Pi相移,相移后相同波长的光密钥与光信号的耦合干涉输出便是对光信号的XOR加密结果,并输出多波长复用的加密信号。通过8×10Gbit/ps的WDM信号的加密仿真得到该方案加密输出误码率(EBR)为0,Q因子为164,证实了方案的可行性与有效性。分析了脉冲占空比对加密输出信号Q因子的影响。通过理论与仿真分析了输入归零码信号占空比对加密信号质量的影响得出,当信号占空比小于0.43时,加密输出信号Q因子能够稳定在164左右。