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.

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.

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.

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。

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.

方位多波束SAR系统中天线长度和PRF选择分析

基于方位多波束合成孔径雷达可以同时实现方位高分辨率和宽测绘带 ,首先简要介绍了方位多波束SAR的基本原理 ,然后详细分析了该系统的方位分辨率与天线长度及脉冲重复频率 (PRF)之间关系。通过与单波束系统对比 ,揭示了方位多波束技术在同时获得高分辨率、宽测绘带方面的优势 ,并探讨了不同分辨率时 ,天线长度、脉冲重复频率选择情况 ,以资工程设计考虑。最后 。

医科达SYNERGY直线加速器PRF EN CHK连锁维修案例

在医科达直线加速器运行过程中,程控脉冲信号发生器(Programmable Pulse Generator,PPG)PCB会发出脉冲重复频率(Pulse Repetition Frequency,PRF)ENABLE信号,依次经过3个控制区和多叶准直器以及直线加速器控制系统(Linac Control System,LCS)回到PPG PCB,如果各区域工作正常,则PPG PCB会向高压部分提供闸流管脉冲触发,脉冲成形网络会正常充放电,磁控管产生微波到加速管加速电子,加速器工作正常。如果PRF ENABLE信号经过的区域有工作异常的情况,则加速器不能正常出束。我院医科达直线加速器的临床使用过程中,多次出现PRF EN CHK连锁。本文总结我院医科达Synergy直线加速器运行过程中出现的PRF EN CHK连锁,详细分析了已出现故障或者可能发生的故障,重点介绍了排除故障的过程,供相关人员参考。

天基雷达的PRF设计

天基雷达可以在全球范围内探测和跟踪运动目标,目前在军用和民用方面受到了广泛的关注。天基雷达通常采用脉冲多普勒工作方式探测运动目标。脉冲多普勒雷达可分为高、中、低脉冲重复频率(PRF)3种类型。选取PRF是脉冲多普勒雷达设计的首要问题。分析了天基雷达检测运动目标的PRF设计相关问题,并对距离和速度模糊的解算方法进行了阐述。

具有多重PRF的雷达回波脉冲视频仿真电路的实现

在目标回波仿真原理的基础上 ,给出了一种新颖的脉冲多普勒雷达目标回波视频脉冲仿真电路。通过计数分频和计数延时技术 ,该电路获得了大范围可变的脉冲重复频率和高精度的脉冲时延 ,能对距离不断变化的动目标进行实时模拟。给出了电路的结构框图 。

一种基于光纤延迟环的低PRF状态测速方法

介绍了PD雷达在低PRF状态下的测速模糊问题。将光纤技术应用于PD雷达,采用光纤延迟环进行脉冲复制,提出了一种可在低PRF状态下进行测速的方法,采用这种方法能够消除低PRF状态测速模糊,提高低PRF状态的测速范围。通过Matlab进行仿真,验证了方法的正确性。

分布式SAR系统PRF误差对ATI测速的影响

分布式SAR采用收发平台分置的飞行方式,具有许多突出优点,但接收机和发射机的PRF会有误差。该文根据收发分置SAR系统原理,建立了收发分置SAR系统PRF误差对成像及干涉的影响模型,研究了PRF误差对ATI相位及测速的影响,并在此基础上提出了对PRF精度的要求。仿真验证了模型的有效性和要求的合理性。

随机变PRF和脉宽的无人机噪声SAR体制研究(英文)

无人机合成孔径雷达(SAR)的抗干扰性能是决定其能否适应现代战场环境的重要因素。为了提高SAR的抗干扰性能,提出了一种随机变脉冲重复频率(PRF)和脉宽的噪声SAR成像新体制。首先,在建立成像模型的基础上对成像算法进行了推导;然后,对随机PRF和随机脉宽的实现方法进行了分析;最后,通过对发射线性调频信号的传统SAR体制与随机变PRF和脉宽的噪声SAR体制在转发式干扰影响下的成像性能进行了仿真比较。仿真结果表明:文中提出的噪声SAR体制相比传统SAR体制具有较好的抗干扰性能。

聚束式合成孔径雷达系统设计中PRF的优化选取

在聚束式合成孔径雷达系统设计中,脉冲重复频率PRF的选择至关重要。在论述SAR系统设计中PRF的限制条件的基础上进一步指出,由于聚束式SAR和条带式SAR在工作模式上存在着本质的区别,两者的方位模糊度的计算方法也有所不同。文中详细地介绍了聚束式SAR的方位模糊度计算函数,阐述了聚束式合成孔径雷达PRF的选取在满足基本限制条件的基础上,可以利用其方位模糊度计算曲线进行进一步的优化。仿真结果表明,这一优化在聚束式SAR系统设计中具有重要意义。

多约束下天基雷达空间目标监视PRF设计

脉冲重复频率(PRF)是天基雷达系统设计中最重要的参数之一。针对天基雷达对空间目标(卫星、空间站等)观测时面临的星下点回波、脉冲遮挡以及地面杂波等问题,提出了一种多约束条件下的斑马图设计方法。根据空间目标轨道分布状况,构建了典型的天基雷达轨道和载荷参数,在传统斑马图设计的基础上,引入了地面杂波的约束条件,并实现了对地面杂波的规避。仿真分析了目标轨道高度和地面杂波对斑马图的影响,仿真结果验证了采用天基雷达对空间目标进行常态化观测的可行性,同时为该情景下的PRF设计提供了参考。