Chaotic Mapping-Based Anti-Sorting Radio Frequency Stealth Signals and Compressed Sensing-Based Echo Signal Processing Technology

Radio frequency (RF) stealth anti-sorting technology can improve the battlefield survival rate of radar and is one of the research hotspots in the radar field. In this study, the signal design principle of anti-sequential difference histogram (SDIF) sorting was explored for the main sorting algorithm of the SDIF. Furthermore, we designed a piecewise linear chaotic system with interval number parameterization based on random disturbance and proposed a method to modulate the repetition period of widely spaced signal pulses using a chaotic system. Then, considering the difficulty of the traditional signal processing method to measure the velocity of the highly random anti-sorting signals designed in this paper, we used compressed sensing (CS) technology to process the echoes of the signals to solve the velocity and distance of the detection targets. Finally, simulation verification was performed from the correctness of the signal design principle, the performance of the chaotic system, the anti-sorting performance of the designed signals and the recovery and reconstruction performance of the signals by CS. The results show that: (a) the signal design principle presented in this paper can guide the signal design correctly; (b) the performance of the piecewise linear chaotic system with interval number parameterization is better than that of the classical one-dimensional chaotic system; (c) the anti-sorting signal modulated by the chaotic system can achieve anti-SDIF sorting, and the anti-sorting signals designed in this paper can be processed to obtain the velocity and distance of the targets.     

任意复包络信号的匀速运动目标回波脉间补偿及相干积累

现代声呐、水下制导等水声探测系统常常使用窄带脉冲、调制、编码、伪随机等种类繁多的发射信号波形来满足低信噪比检测、高分辨估计、抗干扰、主动隐蔽探测的应用需求.针对这一情况,本文研究了任意信号的长时间积累问题,给出了一种任意复包络信号的匀速运动目标回波脉间补偿及相干积累检测方法.通过构建任意发射信号波形的广义模糊函数,将匹配滤波器输出表示为所构造的广义模糊函数,使得任意复包络信号的脉压波形不仅能够用统一的数学模型来表述和计算,而且能够提供多脉冲回波的距离走动信息和多普勒频移信息,为多脉冲距离位置对齐和Fourier变换(FFT)积累提供了依据.对于用广义模糊函数表示的匹配滤波器输出,采用Keystone变换将复包络对齐,消除了距离走动,采用FFT补偿多普勒频移项,实现了任意复包络信号的长时间相干积累.对于水下探测中使用的连续波信号、线性调频信号以及复杂的m序列编码信号、Costas跳频编码信号波形进行了信号积累及检测的计算机仿真,验证了任意复包络信号的匀速运动目标回波脉间补偿及相干积累的正确性.消声水池实验验证了该方法的有效性.     

A bistatic Doppler technique to measure forward scattering at large angles of incidence

We present a bistatic Doppler method to measure forward scatter at large angles of incidence. The Doppler shifted signal avoids contamination by the direct signal between antennae. We illuminated a small area on a rotating table with a 95-GHz transmitter pointed at 60-80° angles of incidence. The area velocity was nearly constant. The scattering media was crushed rock with root mean square (rms) height to wavelength ratio near unity. Although theory precludes Doppler shift for targets moving in the plane of bistatic collinear antennae, shifts occurred at the monostatic backscattering value predicted by twice the table velocity within the illuminated area. The Rayleigh distributions of the Doppler shifted signal, with increasing standard deviation and corresponding decreasing peak amplitude as angle of incidence increased, are expected for the unity ratio, and so verify that Doppler shifted forward scatter was measured. The increased standard deviation with increasing angle is expected because of the increased sensitivity to smaller slope facets of the rock. The reference signal recorded for a metal plate signal also verifies the bistatic Doppler shift and precludes contamination by multiply-reflected backscatter. Minor modifications will allow grazing angle behaviour to be approached. It appears that further theory is needed to understand the bistatic Doppler process.     

旋转镜鼓式热像仪的光雷达回波特性

 旋转镜鼓式热像仪对光场的扫描主要由镜鼓来完成，在激光束的照射下，镜鼓棱及其邻域的后向散射不可避免地给散射光引进了一个附加的多普勒频移。对平行光束经热像仪后的动态回波特性进行分析研究，提出了一种测量光束多普勒频移的方法，并建立了相应的实验系统。实验结果与理论分析是一致的，为判别热像仪的工作方式提供了一种可能的方法。     

1.06 μm相干激光雷达动目标多普勒信号探测

介绍了一套1.06 μm脉冲式相干激光雷达测速演示系统.采用单块非平面环形激光器作为种子,注入到单纵模运转的Q开关高重复频率Nd∶YAG激光器为发射源,实现稳定的单频输出.通过外差式相干探测的方法,利用转速0~60 Hz可调、直径为10 cm的转盘为运动目标,回波信号被带宽为3.5 GHz的高速光电探测器响应后,经采样率为2.5 GS/s的A/D采样,输送到基于LabVIEW信号处理系统中,从而测量不同转速下的多普勒频移,各测速点的多普勒频移测量结果相对误差在3%以内.针对测量中存在的误差从激光器输出线宽和测速系统准确度两方面进行了误差分析,并提出了改进措施.演示系统的良好重复性证实了这种相干激光雷达系统的可行性.     

Dual-signal heterodyne lock-in amplification with lasers

High-sensitivity heterodyne detection with lasers applied to radar and satellite communication is seriously hampered by the large electronic bandwidth due to Doppler shift and frequency instability. These drawbacks can be circumvented by dual-signal heterodyne detection. The system consists of mixing the local oscillator with two signal beams and the lock-in amplification at the beat frequency of the two intermediate frequencies. The signal modulation is demodulated by the lock-in amplification. A detailed analysis of the accompanying noise is given. The derived NEP is much smaller than that of a conventional heterodyne system. As examples, the system is applied to radar and space communication.     

Optimizing chaos-based signals for complex radar targets

There has been interest in the use of chaotic signals for radar, but most researchers consider only a few chaotic systems and how these signals perform for the detection of point targets. The range of possible chaotic signals is far greater than what most of these researchers consider, so to demonstrate this, I use a chaotic map whose parameters may be adjusted by a numerical optimization routine, producing different chaotic signals that are modulated onto a carrier and optimized for different situations. It is also suggested that any advantage for these chaos-based signals may come in the detection of complex targets, not point targets, and I compare the performance of chaos-based signals to a standard radar signal, the linear frequency modulated chirp. I find that I can optimize a chaos-based signal to increase the cross-correlation with the reflection from one complex target compared to the cross-correlation with the reflection from a different target, thus allowing the identification of a complex target. I am also able to increase the cross-correlation of the reflection from a complex target compared with the cross-correlation with the reflection from spatially extended clutter. I show that a larger output signal-to-noise ratio is possible if I cross-correlate with a reference signal that is different from the transmitted signal, and I justify my results by showing how the ambiguity diagram for a chaos-based signal can be different than the ambiguity diagram for a noise signal.     

Doppler shift of a laser pulse beam scattered by a rotating cone and cylinder

Based on laser radar equations, a Doppler shift model of a laser pulse beam scattered by a rotating arbitrary convex target is reported in this paper. The boundary relations between an incident pulse beam and the detected area elements are analyzed by geometric methods. The Doppler shift characteristics of the rotating cone and cylinder are discussed and the difference between the laser pulse beam and the plane wave scattered from the same rotating target is compared accordingly. Numerical simulations show that the Doppler shift is tightly relevant to their dimensions, speeds, and so on. In the same incidence conditions, the pulse beam and plane wave have difference peak values and the same Doppler shift bandwidth. If the waist radius of the pulse beam is larger, the peak value is higher, and the Doppler shifts are proportional to the speed of the rotating target. By virtue of our theoretical model, we probe into the scattered characteristics of the Doppler shifts of a laser pulse beam, which would benefit target identification in national defense.     

Laser Doppler vibrometry based on self-mixing effect

In this paper, a simple, compact and low cost laser Doppler vibrometer is presented. It is simply composed of a laser diode (9 mm in diameter, 2 g of weight, emitting at 825 nm) and by a two-lens optical system designed to focus the laser radiation on the vibrating target. This sensor can measure target velocity. The working principle is based on the self-mixing effect that occurs in a semiconductor laser diode when the emitted radiation is back reflected toward the cavity and then re-introduced inside. The target velocity is calculated measuring the frequency of the peak of the spectrum of the signal generated by a photodiode mounted on the back facet of the laser diode. In this article, the design and the realisation of the vibrometer is reported. The self-mixing vibrometer has been calibrated in the range 0–300 mm/s, using a rotating disk covered with white paper. The effect of the angle of measurement and target distance are reported. Finally, the sensor has been compared with a commercial laser Doppler vibrometer using a vibrating surface as a target.     

Estimating the instantaneous velocity of randomly moving target swarms in a stratified ocean waveguide by Doppler analysis

Doppler analysis has been extensively used in active radar and sonar sensing to estimate the speed and direction of a single target within an imaging system resolution cell following deterministic theory. For target swarms, such as fish and plankton in the ocean, and raindrops, birds and bats in the atmosphere, multiple randomly moving targets typically occupy a single resolution cell, making single-target theory inadequate. Here, a method is developed for simultaneously estimating the instantaneous mean velocity and position of a group of randomly moving targets within a resolution cell, as well as the respective standard deviations across the group by Doppler analysis in free-space and in a stratified ocean waveguide. While the variance of the field scattered from the swarm is shown to typically dominate over the mean in the range-velocity ambiguity function, cross-spectral coherence remains and maintains high Doppler velocity and position resolution even for coherent signal processing algorithms such as the matched filter. For pseudo-random signals, the mean and variance of the swarms' velocity and position can be expressed in terms of the first two moments of the measured range-velocity ambiguity function. This is shown analytically for free-space and with Monte-Carlo simulations for an ocean waveguide.     

Spectral characteristics of a microwave radar signal backscattered by the sea surface at small incidence angles

We present a theoretical analysis of the Doppler-spectrum properties of a microwave radar signal scattered by the sea surface at small incidence angles. The dependences of Doppler-spectrum width and shift on the wind velocity and wave development stage and their azimuthal dependence are analyzed. The case of mixed sea (wind wave plus swell) is also considered. The JONSWAP spectrum model is used to describe sea waves. The study shows that Doppler-spectrum parameters are sensitive to variation of sea-surface state; for example, for the case of developed sea waves, an increase in wind velocity by 1 m/sec leads to increases in the Doppler-spectrum width and shift by 15 Hz and 3 Hz, respectively. It is shown that for the case of a moving radar the Doppler spectrum remains sensitive to variation of sea- surface state with a sufficiently narrow radar directivity pattern. Estimates show that in the case of a single sea- wave system on the surface, using Doppler-spectrum parameters we can, in principle, determine wave type (developing wind wave, developed wind wave, or swell), dominant wavelength, wave propagation direction, and wave height; wind velocity, direction, and acceleration distance can be determined for wind waves.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 5, pp. 517–526, May, 1996.This paper was supported by the Russian Foundation for Fundamental Research (project 93-02-15892).     

Wide-band SAW dispersive filter with a flat amplitude response

It is shown, that a dispersive delay line of a flat amplitude-frequency characteristic in the passband can be synthesized by using the method proposed in reference 1. Such a delay line can be applied in a chirp pulse compression system that exhibits lower side-lobe sensitivity to the Doppler frequency shift of the radar signal.     

Target parameter estimation for OTFS radar using sparse signal processing

In this paper, we consider a monostatic radar receiver for a joint communication and radar (JCR) system that transmits orthogonal time frequency space (OTFS) frames for target detection and parameter estimation. The circular prolate pulse shape (CPPS) is employed over the OTFS signal as it has lower out-of-band (OoB) power radiation in comparison with the rectangular pulse shaped (RPS) OTFS. The PAPR of CPPS OTFS signal shows lowest value for larger frame duration and hence the signal can be considered to be a good candidate for JCR system. In the Delay-Doppler (DD) domain, the radar channel is sparse and therefore, we model the target detection problem as a sparse recovery problem to generate target profiles with higher peak-to-sidelobe ratio (PSLR). The target detection is carried out in the DD domain, the time–frequency (TF) domain, and in the time domain (TD). Sparse signal recovery algorithms like the orthogonal matching pursuit (OMP) algorithm, the subspace pursuit (SP) algorithm, and the sparse Bayesian learning (SBL) based algorithm are used in target parameter estimation. The performance of these algorithms are compared in terms of their computational complexity, the root mean squared error (RMSE) in the estimates of range and velocity and PSLR value in the target profiles. Simulation results validate that the proposed CPPS OTFS based radar system could detect the targets accurately in all the three domains and produce target profiles with almost zero side lobes.     

基于频谱Sevcik维数的目标运动速度估计*

在声目标无源估计应用中,目标与接收器存在相对运动时,接收的目标辐射的噪声信号存在多普勒频移。多普勒频移中包含目标的运动参数信息。针对线谱信号多普勒频移目标运动参数获取问题,提出一种基于频谱Sevcik维数的目标运动速度获取方法。首先利用Doppler-warping变换对接收信号进行重采样,然后对重采样后的频谱信号求Sevcik维数,最后通过寻找Sevcik最小值来实现速度估计。仿真证实了所提方法的有效性,在相同仿真条件下,所提方法相较于频谱求熵算法,速度搜索结果不仅具有更窄的主瓣宽度,而且可提高抗噪性5dB左右。两组实验数据的速度估计误差小于5%,证明了本文算法的有效性。     

时频分析在激光多普勒信号处理中的应用

建立了用来检测微机电系统谐振器面内运动的激光差动多普勒系统,测量了谐振器的振动速度。在信号处理过程中,首先使用电路系统去除高频载波成分,然后基于Matlab平台,选取时频分析中的Wigner-Ville分布对采集进入计算机的多普勒信号进行分析。提取了其中的速度信息,并与用计数法处理的结果进行了比较。结果表明具有较好的效果。     

基于数字存储示波器的超声多普勒效应实验系统的研究与应用

介绍了一种基于数字存储示波器的超声多普勒效应实验系统.该系统利用现有的超声声速测量设备,以频移信号处理电路和数字存储示波器作为数据测量单元的核心,通过与系统底座和运动控制单元相配合,开展与多普勒效应相关的多项综合性、设计性实验.实验中信号的转换、传输和处理过程清晰透明,有利于培养学生的自主动手能力和观察分析问题的能力.该实验系统结构简单,无需复杂的软件编程,各实验室均可自行完成制作,同时又可实现实验资源共享,提高仪器设备的利用率,具有较高的实用和推广价值.     

Doppler angle and flow velocity mapping by combined Doppler shift and Doppler bandwidth measurements in optical Doppler tomography

Accurate estimation of flow velocity requires measurement of Doppler angle, which is not available in general clinical applications. We describe a novel method of direct Doppler angle and flow velocity mapping that uses a conventional single-beam optical Doppler tomography system. The Doppler angle is estimated by combination of Doppler shift and Doppler bandwidth measurements, and flow velocity is calculated from the Doppler shift and the estimated Doppler angle. In vivo study of lip microvascularization demonstrates that this method is capable of providing both flow speed and flow direction information.     

Doppler spectra of laboratory wind waves at low grazing angle

Eight radar frequencies over a range from 3 GHz to 94 GHz have been used to measure Doppler spectra of wind waves in a laboratory wind-wave tank, at low grazing angle. The VV spectra show relatively little change in shape at different frequencies. The HH spectra show significant trends in the lower radar frequencies, some of which are probably artefacts of the experiment. A new model, the 'fish model' is developed empirically from measurements of the peak Doppler spectra for both vertical and horizontal polarization. This model indicates that the H-pol, not just the V-pol, peak Doppler shift is dependent on the radar frequency.     

基于可调谐半导体激光吸收光谱技术的高速气流流速测量方法研究

以激光Doppler效应为原理,结合可调谐半导体激光吸收光谱技术的窄线宽、可调谐优势, 可实现高速气流流速的实时在线检测.介绍了流速测量的基本原理和方法,搭建了双光路流速测量系统, 利用DFB激光器对位于1398 nm处的水汽吸收线进行10 kHz快速扫描,获得高速气流的实时光谱信息, 并根据两路吸光度曲线之间的Doppler频移来反演气流流速.介绍了频率标定和Doppler频移测量的方法. 在风洞上进行了流速测量验证性实验,将流速测量结果与理论计算结果进行了对比,二者之间符合得较好, 初步证明了该方法的可行性.分析了系统的性能及可能引起流速测量误差的因素,以便系统进一步优化.     

Measurement and direct regulation of the velocity of a fast beam using doppler-tuned laser photon-atom interactions

An optical method is described that uses the Doppler shift to measure the velocity of a fast particle beam merged with a photon beam from a laser. The Doppler-tuned resonance signal is used in a feedback loop to regulate directly the velocity of the beam. The method is demonstrated using a beam of ⁴He atoms pumped by CO₂ laser photons into high Rydberg pure quantum states. Applications to other areas of fast beam physical research are discussed.