高重频雷达导引头变PRF抗遮挡方法设计

针对高重频PD雷达测距模糊,不能直接利用距离信息抗距离遮挡的问题,提出了一种高重频雷达导引头变PRF抗遮挡方法;对限定频率范围内的PRF进行分析,根据优选策略确定一组具备抗遮挡能力的PRF,针对载机能否提供较精确的初始装订距离,分别设计不同的PRF切换方式,由导引头软件控制优选PRF组按照不同的方式切换工作,完成抗遮挡任务;仿真试验结果表明:提出的方法具有较好的抗遮挡性能。

雷达导引头三种抗遮挡技术的适用性分析

针对脉冲体制主动雷达导引头存在遮挡问题,在阐述遮挡效应及其对导引头影响的基础上,分析了变重频、遮挡外推和遮挡预判三种抗遮挡技术。分析表明:对于宽带导引头,可采用变重频抗遮挡技术消除遮挡;对于窄带导引头,可结合遮挡外推和遮挡预判技术降低遮挡影响。

一种星载高分辨率SAR的非基带插值方位预处理方法

星载高分辨率滑动聚束SAR系统采用方位向大转角技术来实现高分辨率与宽测绘带的折中,系统在大转角时场景回波的距离徙动非常大,单一回波窗无法适应大距离徙动。基于这一问题本文提出一种非基带插值方位预处理方法,系统采用分段变重频技术实现对回波的全覆盖。通过二维时域对回波沿方位向分块,采用非基带插值对分段后的时域信号进行重采样,得到不同PRF下的均匀化数据。仿真结果表明,该方法有效实现了数据的均匀化预处理,与传统处理方法相比成像结果的方位分辨率提高,PSLR、ISLR得到4 d B以上的改善。

A WEIGHTED GENERAL DISCRETE FOURIER TRANSFORM FOR THE FREQUENCY-DOMAIN BLIND SOURCE SEPARATION OF CONVOLUTIVE MIXTURES

This letter deals with the frequency domain Blind Source Separation of Convolutive Mixtures (CMBSS). From the frequency representation of the "overlap and save", a Weighted General Discrete Fourier Transform (WGDFT) is derived to replace the traditional Discrete Fourier Transform (DFT). The mixing matrix on each frequency bin could be estimated more precisely from WGDFT coefficients than from DFT coefficients, which improves separation performance. Simulation results verify the validity of WGDFT for frequency domain blind source separation of convolutive mixtures.

Three-Step Damage Identification Method Based on Dynamic Characteristics

A three-step damage identification method based on dynamic characteristics is proposed to improve the structure reliability and security and avoid serious accident. In the proposed method, the frequency and difference of modal curvature(DMC) are used as damage indexes. Firstly, the detection of the occurrence of damage is addressed by the frequency or the square of frequency change. Then the damage location inside the structure is measured by the DMC. Finally, with the stiffness reduction rate as a damage factor, the amount of damage is estimated by the optimization algorithm. The three-step damage identification method has been validated by conducting the simulation on a cantilever beam and the shaking table test on a submerged bridge. The results show that the method proposed in this paper can effectively solve the damage identification problem in theory and engineering practice.

Research on RF Cavity Tolerance of CYCIAE-100

The tolerances of the manufacture and installation errors and Dees deformation caused by gravity in RF cavity of CYCIAE-100 are investigated.Both the analytic treatment and numerical simulation are carried out to give the tolerance of the manufacture and installation errors which disturb the radial and vertical motion of the beam.The Dees deformation caused by gravity leads to axial misalignment of the Dees and then induces the build-up of coherent axial oscillations.However,the calculated results show that the deformation of our Dees is acceptable.

Partial discharge characteristics of interturn insulation used for inverter-fed traction motor under bipolar impulses

Inverter-fed traction motors,which are employed for electric-multiple-units(EMUs),are subjected to Pulse Width Modulated(PWM) impulse voltage.Impulse voltage has fast rise/fall time and high repetition frequency.The failure mechanism of insulation under impulses is different from that of standard 50 Hz sinusoidal condition.Partial discharge(PD) characteristics(discharge number,mean discharge quantity and phase resolved partial discharge(PRPD) pattern) with different frequencies and different rise times of impulse voltage were investigated.The results reveal that discharge number and mean discharge quantity increase,while PRPD pattern moves to the zero of impulse voltage with decrease of rise time.Discharge number and PRPD pattern follow that trend with increase of frequency,the value of mean discharge quantity is similar.Memory effect of the deposited space charges on PD was studied.PRPD pattern moves to the zero of bipolar impulse voltage due to the role of space charges,with increase of frequency and decrease of rise time.It is revealed that available discharge time is prolonged and overvoltage across the cavity increases with augment of frequency,which results in discharge number increasing.Under the condition of shortening the rise time,with the same statistical time lag tL,△V would increase if dV/dt is higher,which results in enhancement of discharge quantity.Discharge number increases with reduction of rise time,because the decreased multiple of td is lower than the increased multiple of dV/dt.Study of PD characteristics and role of space charges is helpful to the exploration of the destructive mechanism of insulating materials under bipolar impulse.

Generation of picosecond vortex beam in a self-mode-locked Nd:YVO4 laser

In this paper, a self-mode-locked Nd:YVO_4 picosecond vortex laser is demonstrated, which can operate on the different Laguerre-Gaussian(LG) modes at 1 064 nm. A π/2 mode converter is utilized to realize the picosecond vortex laser with LG mode transformed from the high-order Hermite-Gaussian(HG) mode. For the proposed laser, the mode-locked pulse repetition rate is 1.81 GHz. The average output powers of LG_(12) mode and LG_(02) mode are 1.241 W and 1.27 W, respectively, and their slope efficiencies are 23.2% and 24%, respectively.