Velocity compensation methods for LPRF modulated frequency stepped-frequency(MFSF) radar

In the high speed target environment,there exists serious Doppler effect in the low pulse repetition frequency（LPRF） modulated frequency stepped frequency（MFSF） radar signal.The velocity range of the target is large and the velocity is high ambiguous,so the single method is difficult to satisfy the velocity measurement requirement.For this problem,a novel method is presented,it is a combination of cross-correlation inner frame velocity measurement and range-Doppler coupling velocity measurement.The cross-correlation inner frame method,overcoming the low Doppler tolerance of the cross-correlation between frames,can obtain the coarse velocity of the high speed target,and then the precision velocity can be obtained with the range-Doppler coupling method.The simulation results confirm the method is effective,and also it is well real-time and easy to the project application.

Discharge Characteristics of SF_6 in a Non-Uniform Electric Field Under Repetitive Nanosecond Pulses

The characteristics of high pressure sulphur hexafluoride（SF6） discharges in a highly non-uniform electric field under repetitive nanosecond pulses are investigated in this paper.The influencing factors on discharge process,such as gas pressure,pulse repetition frequency（PRF）,and number of applied pulses,are analyzed.Experimental results show that the corona intensity weakens with the increase of gas pressure and strengthens with the increase of PRF or number of applied pulses.Spark discharge images suggest that a shorter and thicker discharge plasma channel will lead to a larger discharge current.The number of applied pulses to breakdown descends with the increase of PRF and ascends with the rise of gas pressure.The reduced electric field（E/p） decreases with the increase of PRF in all circumstances.The experimental results provide significant supplements to the dielectric characteristics of strongly electronegative gases under repetitive nanosecond pulses.

高速机动平台SAR成像PRF设计方法

在高速机动平台合成孔径雷达(Synthetic Aperture Radar,SAR)成像系统中,现有脉冲重复频率(Pulse Repetition Frequency,PRF)设计方法基于方位向信号带宽计算出的下限值过高,且忽视了雷达的工作占空比因素。针对上述问题,首先推导了一组避开发射脉冲干扰、平台正下方回波干扰以及距离向模糊等因素的关联PRF和雷达工作占空比的约束方程,然后提出了一种距离向分段SAR成像处理情况下的PRF下限值设计方法。仿真结果表明,在机动平台高速运动大前斜视聚束SAR成像时所提方法能够得到较小的PRF下限值,有效扩展了PRF可选择的范围,可以更好地满足实际工程应用。

High efficiency sub-nanosecond electro-optical Q-switched laser operating at kilohertz repetition frequency

Based on a theoretical model of Q-switched laser with the influences of the driving signal sent to the Pockels cell and the doping concentration of the gain medium taken into account,a method of achieving high energy sub-nanosecond Q-switched lasers is proposed and verified in experiment.When a Nd:YVO4 crystal with a doping concentration of 0.7 at.%is used as a gain medium and a driving signal with the optimal high-level voltage is applied to the Pockels cell,a stable single-transverse-mode electro-optical Q-switched laser with a pulse width of 0.77 ns and a pulse energy of 1.04 mJ operating at the pulse repetition frequency of 1 kHz is achieved.The precise tuning of the pulse width is also demonstrated.

Generation of X-ray Emission in Repetitive Nanosecond-pulse Discharge at Atmospheric Pressure

Pulsed discharges can generate high power densities and high equivalent electric fields in plasma to emit X-rays,which is closely related to discharge mechanism.In this paper,discharge characteristics and X-ray emission of typical nanosecond-pulse discharges(corona,diffuse,spark or arc)are reviewed.Especially,the diffuse discharges are observed at pulse repetition frequencies up to 1 kHz.Factors influencing the discharge characteristics and X-ray emission are analyzed,such as the gap spacing,parameters of the applied pulse(amplitude,pulse repetition frequency),anode and cathode materials,and curvature radius of cathode.It is concluded that the maximum X-ray intensity is obtained in a diffuse discharge,and the X-ray intensity is affected by the pulse repetition frequency,applied voltage,anode material,and curvature radius of cathode.For example,X-ray intensity increases with the pulse repetition frequency and the atomic numbers of the anode material,but it decrease with the increase of curvature radius.It is also shown that the cathode material has no obvious influence on the X-ray intensity.

Generation of Atmospheric Pressure Plasma by Repetitive Nanosecond Pulses in Air Using Water Electrodes

Dielectric barrier discharge （DBD） excitated by pulsed power is a promising method for producing nonthermal plasma at atmospheric pressure. Discharge characteristic in a DBD with salt water as electrodes by a home-made unipolar nanosecond-pulse power source is presented in this paper. The generator is capable of providing repetitive pulses with the voltage up to 30 kV and duration of 70 ns at a 300 Ω resistive load. Applied voltage and discharge current are measured under various experimental conditions. The DBD created between two liquid electrodes shows that the discharge is homogeneous and diffuse in the whole discharge regime, Spectra diagnosis is conducted by an optical emission spectroscopy. The air plasma has strong emission from nitrogen species below 400 nm, notably the nitrogen second positive system.

A Gain-Switched Fe:ZnSe Laser Pumped by a Pulsed Ho,Pr:LLF Laser

We demonstrate a gain-switched Fe:ZnSe laser pumped by a 2958 nm pulsed Ho,Pr:LLF laser. The maximum single pulse energy is 16.4uJ with a minimum pulse duration of 13.9 ns at the pulse repetition frequency of1 Hz when the Fe:ZnSe crystal is cooled to 77 K by liquid nitrogen, corresponding to a slope efficiency of 22.9%.The central wavelength and FWHM linewidth are 3957.4 nm and 23.2 nm, respectively. The output energy monotonically decreases as the crystal temperature increases in the range 77–293 K.

The pulsed microwave damage trend of a bipolar transistor as a function of pulse parameters

In the present paper we conduct a theoretical study of the thermal accumulation effect of a typical bipolar transistor caused by high power pulsed microwaves（HPMs）,and investigate the thermal accumulation effect as a function of pulse repetition frequency（PRF） and duty cycle.A study of the damage mechanism of the device is carried out from the variation analysis of the distribution of the electric field and the current density.The result shows that the accumulation temperature increases with PRF increasing and the threshold for the transistor is about 2 kHz.The response of the peak temperature induced by the injected single pulses indicates that the falling time is much longer than the rising time.Adopting the fitting method,the relationship between the peak temperature and the time during the rising edge and that between the peak temperature and the time during the falling edge are obtained.Moreover,the accumulation temperature decreases with duty cycle increasing for a certain mean power.

Investigation of Nanosecond Pulsed Discharge and Its Audio Characteristics in Atmospheric-pressure Air

There was no well-resolved mechanism of audible noise caused by corona discharge on UHV transmission lines. Hence we measured the sound pressure of pulsed discharges between needle-plane electrodes under different discharge conditions in air, for revealing the intrinsic relationship between discharge and its audible noise(AN). The relationship between discharge parameters and audio characte- ristics was drawn from the analysis of the electric and sound signals obtained in experiments. Experiment results showed that nanosecond pulsed discharges produce the sound pressure with a microsecond pulse lagging behind the discharge pulse in their waveforms. The peak value of the sound pulse decreases and its high frequency component gradually attenuates, when the measuring distance from discharges increases. The sound pulses correlate with the discharge current and voltage significantly, especially the current. The audible noise produced by repetitive pulsed discharge increases with the strength, duration, and pulse repetition rate of discharge.

HPRF和差天线雷达导引头杂波抑制方法

高脉冲重复频率(high pulse repetition frequency,HPRF)和差天线雷达在导引头中具有重要应用,其在超低空运动目标检测时,面临多重距离模糊的地海面杂波抑制问题。针对上述问题,提出一种和差通道时域对消的杂波抑制方法。该方法基于和差通道间杂波功率谱相关度较高的特征,联合利用差-差-双差通道数据估计杂波协方差矩阵,拟合和通道的杂波协方差矩阵,并基于最小方差准则实现和通道杂波对消,提升了雷达导引头的杂波抑制性能。仿真实验验证了该方法的有效性。

重复频率微波脉冲大气击穿延时与电离率

针对高功率微波在大气传输中可能出现的击穿现象,研究了脉冲序列中首次脉冲击穿延时和后续脉冲击穿延时,研究结果发现首次脉冲击穿延时在脉宽范围内大致均匀分布,后续脉冲击穿延时波动性较小。根据击穿延时数据对电离率进行了分析,指出在重复频率条件下,初始电子密度较高,电子密度分布不适用指数分布,无法用延时数据标准差对电离率进行估计。提出了一种用重复频率脉冲击穿延时数据计算电离率的方法,并将计算结果与仿真结果进行了对比,结果显示,二者有较好的对应关系。

激光触发多门极半导体开关初步研究

固态脉冲功率源在脉冲功率技术领域应用广泛,已经成为新的研究热点,其中,高功率固态开关器件是固态脉冲功率源的核心。报道了一种新型光触发多门极半导体开关(LIMS),该开关具备光致线性模式和场致增益模式两种工作模式,解决了传统电控器件电流上升率低的问题,实现了器件的高电流上升率,光致线性模式下实验测试得到了454 kA/μs的电流上升率,该开关在雷管起爆、电磁脉冲模拟等领域已得到初步应用。

基于遗传算法的机载中重频高效多维优化

机载脉冲多普勒(PD)雷达的重频组设计是雷达总体设计的基础,直接影响雷达的性能和应用场景。在中重频组设计过程中,必须考虑多维度参数的优化,由于可调整参数多,会导致潜在组合数膨胀严重,对计算资源和时间提出了极大的挑战。传统的优化方法,即便在限定参数范围后,仍面临穷举组合数庞大的问题。此外,机载雷达系统设计周期通常较短,模式需求多变,需要在较短时间内完成方案前期参数的选择和初步优化,便于开展后续设计。本文提出了一种基于遗传算法的高效多维优化方法,不仅增加了优化维度以更好满足工程需求,同时显著提升了优化效率。通过应用实例验证了所提方法的有效性,对机载PD雷达总体设计论证具有重要价值。

高重复频率被动谐波锁模光纤激光器研究进展

被动谐波锁模(HML)技术作为一种快速提高光纤激光器输出脉冲重复频率的有效方法,显著提升了光纤激光器的输出脉冲重复频率。该技术通过在激光器内部集成参数可调的可饱和吸收体,实现了高阶谐波输出,从而大幅提高了脉冲重复频率。综述了目前被动HML光纤激光器中常用的几类可饱和吸收体,详细阐述了它们的技术原理及优势,并分析了国内外该领域的最新技术进展。最后,指出了被动谐波锁模光纤激光器的未来发展趋势。

滚动轴承润滑膜厚及保持架转速的超声测量

滚动轴承的运行稳定性与钢球和内外圈之间的润滑状态密切相关,膜厚则是表征轴承润滑性能的重要参数。基于超声弹簧模型建立了膜厚测量模型并搭建了试验台,通过试验台模拟球轴承的运行状态并测量钢球周围以及沿滚动方向的膜厚分布,分析了转速对最小膜厚的影响;同时,根据连续2个钢球通过探头正下方的时间间隔计算保持架转速,分析得到了不同重复频率所能测量的保持架转速范围。试验结果表明,膜厚的实际测量值与理论值吻合较好,保持架转速的实际测量值与纯滚动条件下的理论转速一致性良好,可用于轴承打滑状态的评估。

猝发重频高压大功率脉冲充电电源研制

针对电感隔离型重频Marx发生器的充电需求,研制了一台猝发重频高压大功率脉冲充电电源。该电源采用直流电源+储能电容+晶闸管开关+脉冲变压器的技术路线,设计指标为充电电压为90 kV,充电电流1 kA,充电重复频率1 Hz~100 Hz可调,猝发工作时最大充电次数为5次。首先介绍了充电电源的工作原理,进行了电路参数计算和结构设计,得到了晶闸管、初级电源和脉冲变压器等主要器件的参数。然后试制组装了一套电源,并进行了实验验证:对等效总电容量为0.7μF的紧凑型Marx发生器充电时,充电电压90 kV,充电时间小于120μs,充电重复频率10 Hz。该电源的研制成功对高功率重复频率脉冲功率源的进一步小型化具有重要意义。

低脉冲重复频率条件下无人机微动参数提取

针对低脉冲重复频率条件下的无人机微动特征提取问题,提出一种基于原子放缩正交匹配追踪(orthogonal matching pursuit,OMP)分解的微动参数估计方法。首先,通过计算时频谱熵从无人机回波数据中筛选出具有显著微动特征的信号。其次,采用变分模态分解(variational modal decomposition,VMD)算法提取旋翼叶片的旋转频率,提出了基于原子放缩的OMP分解方法实现了对无人机旋翼叶片长度的估计。仿真实验表明所提方法相比于传统的OMP方法和VMD-OMP方法都具有明显优势。最后,采用实测数据验证了所提算法的有效性。

辉光放电触发重频伪火花开关研究

伪火花开关是工作在帕邢曲线左支的低气压开关,具有纳秒级击穿时间、百千安级脉冲电流、工作寿命长等特点。具有高重频性能的伪火花开关民用领域以及军事领域均有广泛的应用需求。基于双脉冲辉光放电触发结构,设计出一种具有重频能力的伪火花开关;在10 kV阳极电压下进行了整管测试,观察不同气压,预、主触发电压对重频性能以及触发性能的影响;结合仿真软件计算不同气压与触发电压下,触发电流的变化,最终总结了两个脉冲对触发过程的影响。测试结果表明,最低仅100 V触发电压,开关重复频率即可从沿面放电触发的100 Hz提升至400 Hz。

基于贝叶斯方法的HPRF雷达跟踪解距离模糊方法(英文)

高脉冲重复频率(HPRF)雷达目标跟踪需要解决距离模糊问题。本文通过把脉冲间隔数和脉冲间隔变化量作为目标的离散状态,目标的距离和径向速度作为目标的连续状态,将HPRF雷达的跟踪和解距离模糊问题转换为贝叶斯框架下的混合估计问题并且利用粒子滤波方法实现。仿真结果表明本文方法在脉冲间隔数变化时仍可以正确地解距离模糊,并且跟踪精度比多假设方法高。

HPRF雷达距离延拓检测前跟踪方法

针对高脉冲重复频率(HPRF)雷达弱小目标检测前跟踪的距离模糊问题,提出了一种基于距离延拓的检测前跟踪方法.该方法采用多重频参差工作模式,对动目标检测器(MTD)处理后的数据进行预处理,并按照不同的距离模糊数进行距离延拓.通过多重频组内直接能量积累和组间的航迹能量积累获取最大的目标能量.最后,采用航迹凝聚策略消除由动态规划算法引起的航迹团聚效应,依据虚假目标与真实目标的相关性去除由低信噪比而引起的虚假目标航迹.在未知目标初始化状态的情况下,该方法提高了对弱小目标的检测性能.仿真结果表明了该方法的有效性.