连续波声呐中的调频信号设计方法及性能分析

相对传统的短时脉冲波主动声呐而言,连续波主动声呐是一种新型体制的声呐设备,允许在扫描周期内发射高占空比的信号,并且在发射信号的同时进行侦听,由此可以对水下目标实现连续照射,消除距离盲区。由于发射和接收机制的不同,连续波主动声呐对发射信号的波形和处理方法也各有差异,一是要考虑到"直达波"抑制问题,二是要在时间带宽积和对目标的照射时间间隔两者之间进行折中。针对上述两个问题,设计了一种在连续波主动声呐中发射的新型脉冲串信号,该类信号由多个相互正交的广义正弦调频信号串组成,以此在频域上消除回波与拷贝信号的相关性;后置处理中对接收回波提供了三种不同的方案,在时间带宽积和照射时间间隔两者之间择优选择最佳检测效果。计算机仿真结果表明:该类信号波形以及相应的处理方法可以有效地抑制直达波干扰并给出目标的速度-距离信息。     

合成孔径雷达线性调频信号的线性度约束研究

合成孔径雷达(SAR)发射的信号为线性调频信号，由于受系统的影响，频率和时间并不满足线性关系，可能会发生某种畸变．这样就会存在一个线性度的问题．本文描述了线性度对于调频信号的压缩产生的影响，并且利用压缩信号的特点得到了对于线性度的具体约束，然后通过仿真验证了约束的正确性．     

一种连续波雷达调制参数测试仪

连续波雷达调制参数测试仪是对雷达发射机的复合调制参数进行测试的综合性仪器。本文着重介绍了该测试仪的设计思想、工作原理，并对研制中的一些技术问题作了说明。     

调频信号发射超声成像的参数优化与成像实验

研究调频信号发射超声成像中影响成像质量的各种参数,提高现有超声图像的信号噪声比.用仿真计算和声学实验来研究不同调频超声信号发射参数下的成像质量.增加超声发射能量,提高图像的信号噪声比;同时,采用相关算法对接收的超声信号解码,保证图像的轴向精度不会下降.优化了调频信号发射超声成像的发射参数,并得到了仿体的B型超声图像,此图像的质量优于传统成像方法的图像质量.该成像方法能够提高超声图像的信号噪声比,尤其是提高超声衰减严重的深部组织图像的信号噪声比.     

线性调频信号检测的快速调频变换算法

线性调频（LFM）信号是雷达和声呐系统中常用的宽带信号。介绍了一种快速调频变换算法,用于线性调频信号的检测。首先对该方法进行了详细的推导和讨论,讨论了该快速算法中使用到的部分傅立叶变换快速算法,并研究了快速调频变换算法的计算量。最后,实验表明了快速调频变换算法有良好的信号检测性能。     

基于H∞滤波器的多分量线性调频信号参数估计

针对多分量线性调频信号数据长度较短的情况，利用多分量线性调频信号的时空域信息，将其分解成多个单分量线性调频信号。针对未知噪声的情况，利用有限长H∞滤波器的良好瞬时特性和鲁棒特性，对每个单分量线性调频信号的参数进行估计，进而实现多分量线性调频信号参数估计。由于采用H∞平方根估计算法，此方法能够抑制递推计算的发散。计算机仿真表明了此方法的有效性。     

线性调频信号在低频振动校准系统中的应用

针对某低频(0.01～20Hz)电动振动台校准系统存在的校准时间长、精度低、费用高等不足,利用虚拟仪器技术对其进行扩展和完善;针对原系统由于采用单频正弦信号进行人工扫频的校准方法,而导致的校准时间长,且对于被校传感器的某些谐振点无法精确测得等缺点,介绍了采用低频段内的线性调频信号作为激励信号的校准方法,有效地实现了一定频率段内快速、高精度的校准.提出了在校准过程中将调频信号校准方法和正弦信号校准方法有机结合的新方案.通过理论分析和试验结果表明,此校准方法具有较好的实用价值.     

一种线性调频信号的设计

雷达的信号波形作为现代雷达系统的一个重要组成部分,在雷达系统中起着至关重要的作用。简要介绍DDS器件GM4940的特点,并着重叙述基于GM4940的线性调频信号的设计方法。最后给出利用GM4940产生的线性调频信号的测试图片。     

线性调频信号激励超声换能器的方法研究

针对超声换能器的特性,研究等幅及包络调制线性调频波的换能器激励响应。通过对比激励前后脉冲压缩的主瓣峰值、?3d B主瓣带宽和峰值旁瓣水平,探讨通过换能器后其信噪比和分辨率的性能。理论分析和仿真实验结果表明,两种调频信号通过换能器后信噪比和分辨率都减少,峰值旁瓣有所提高。包络调制线性调频信号激励换能器脉冲压缩的信噪比和分辨率高于等幅线性调频信号,但能量损失比等幅线性调频信号大。     

线性调频半导体激光定位的研究

本文提出了一种半导体激光定位技术，它利用半导体激光器的线性调频特性来实现干涉零点的动态定位，突破了传统白光定位的局限，简化了干涉仪设计，并实现了大范围内的零点捕，是一种实用的干涉定位技术。，     

基于时频分布的线性调频信号波达方向估计

1引言 波达方向(DOA:Direction of arrival)估计是雷达和声纳系统中的一个重要问题.传统阵列高分辨算法一般基于信号的平稳假设,然而在许多实际场合,信号是非平稳的或谱时变的,如雷达信号和声纳信号.其中线性调频信号(LFM:Linear Frequency Modulated)是常用的信号形式之一,具有明显的时频分布特性,因此本文以LFM信号为例进行讨论.时频分析是处理非平稳信号的有效手段,它将一维的时间信号变换到二维的时频域,揭示了信号中每一频率分量随时间的变化趋势[1].     

基于Wigner-Hough变换改进算法的多分量LFM信号检测

Wigner-Hough变换可以很好的抑制多分量LFM信号Wigner-Ville分布中严重的交叉项,但是在低信噪比时,Wigner-Hough变换完全被噪声淹没.本文提出一种改进算法,用基于信号的自适应高斯核时频分布代替Wigner-Hough变换中的Wigner-Ville分布.仿真表明,对于多分量信号在信噪比为-3dB,单分量信号在-17dB时该算法仍然有很好的性能.     

A Wide-Range CW Power Measurement Technique

An accurate power measurement technique is described, which makes possible the determination of the net power delivered to a load of arbitrary impedance over a wide power range. A standard power meter is employed to fix a reference power level. Subsequent measurements consist of dimensionless ratios that can be obtained from precision attenuators. The method is applicable to a very wide range of frequencies and was demonstrated at a frequency of 30 MHz with power measurements extending from 10-2 to 10-14 watt. Maximum uncertainties ranged from ~0.5 to 1.5 percent. This technique is applicable in the measurement of the sensitivity of very-low-level detectors, receivers, radiometers, etc.     

Dynamic Testing of Historic Towers Using an Interferometric Radar from an Unstable Measurement Position

Interferometric radar is a rather popular equipment able to remotely perform dynamic testing of large structures (towers, bridges, buildings?…) by detecting the relative displacement in the line of sight between the radar and geometric discontinuities in the engineering structure under test. This technique has been demonstrated effective when the radar is positioned at ground on a stable position. Unfortunately there are practical cases for which a suitable stable position is not available. This is the case of the towers of San Gimignano (Italy) that are embedded in the narrow streets of the old town. A solution to monitor the towers is to install the radar on the top of a tower, which is located in a central position of the town. The tower is not a stable arrangement for the radar and in this paper the authors propose and test the use of an accelerometer fixed to the radar head for detecting and removing its own movement.     

A Novel Method of Distance Measurement Based on Pulse Position Modulation and Synchronization of Chaotic Signals Using Ultrasonic Radar Systems

This paper deals with a novel method of transmission and receipt of a signal based on both the property of two chaotic systems generating the same chaotic signal when they are synchronized and the property of pulse position modulation (PPM) to be insensitive to the distortions of the transmission channel. The method is discussed in the context of ultrasonic radar systems, in which the transmitter and receiver, which consist of ultrasonic sensors, are near each other, and the received signal consists of the transmitted signal reflected by an obstacle. A reference sinusoidal signal is superimposed to a chaotic signal generated by a master chaotic system, and the whole signal is modulated according to the PPM method and transmitted by the sensor. The received signal is demodulated, and the demodulated signal forces a slave chaotic system to generate the chaotic signal embedded in it, which allows recovery of the sinusoidal signal by subtracting this chaotic signal from the demodulated echo. The difference of the phases of the reference sinusoidal signal and the recovered sinusoidal signal allows computation of the time of flight of the signal and, consequently, the distance of the radar system from the obstacle. The novel method is illustrated and tested by both simulation and experiments. The interference problem between the considered radar system and other radar systems ( crosstalk) is also addressed, and a solution is proposed to avoid it.     

Measurement of absolute distance employing a tunable CW dye laser

With a tunable CW dye laser oscillating in a single longitudinal mode, measurement of an absolute distance is demonstrated with the method of excess fractions. Five beams which have different wavelengths are emitted sequentially from the dye laser, and the interferometric phase is measured for each wavelength. An interferometric order number for a wavelength can be calculated from values of wavelengths and phases. Then a precise value of length is obtained. This method is similar to measuring distances by using group delay as used in VLBI and microwave ranging. The measured accuracy was within ±8.8 nm between 0 and 10 mm (at an absolute distance of 0.1-10.1 mm)     

电子信号频率测量方法的误差分析

本文介绍了应用于电子信号频率测量的直接测频法、测周期法和变闸门测频法,分析了测量误差的产生原因,推导出这三种测量方法的相对误差公式,在较宽的频率测量范围内分析了相对误差的特点和变化规律,从而证明了变闸门测频法是一种高精度、宽量程的频率测量方法.     

Dynamic Properties of Laser Speckles on Images Transmitted Through an Image Fibre-bundle

Abstract

The statistical properties of time-varying laser speckles appearing on an image transmitted through an image fibre-bundle are studied experimentally and theoretically. The effect of defocusing on a stage of observation is investigated in relation to the stationarity of the detected speckle intensity. It is shown that a large amount of defocusing produces a stationary speckle field for which the correlation function of the speckle intensity variation is obtained in a stable form. This allows a system for monitoring the velocity of moving objects using an image fibre-bundle to be developed.     

非均匀采样信号的能量/功率测量

本文分析了采样信号的非均匀性对于能量／功率测量的影响，推导了非均匀采样信号在时域与频域上的能量对应关系，得出了利用非均匀采样序列计算信号的能量／功率收敛于真值的条件。仿真结果验证了理论的正确性。