低副瓣气象雷达天线增益测量及误差分析

简述了低副瓣S波段8.54 m气象雷达天线的基本特性,提出利用方向图积分法计算天线方向性增益,扣除方向图有限积分区域引起的增益损失、漏失损失、交叉极化损失、失配损失和馈源网络插入损耗,从而确定天线增益的方法。给出了各种增益损失因子的计算公式,分析了方向图积分法测量天线增益误差,其均方根误差≤"0.224 dB。最后给出了S波段8.54 m气象雷达天线增益的实测结果,测量结果同理论结果吻合很好。     

键盘按键信息的近场截获研究

计算机键盘在正常工作时会伴随产生电磁骚扰噪声,未授权人员若窃取这些电磁噪声经分析处理便可还原键盘的按键信息.经测试发现键盘的电磁辐射主要来自键盘内的印制电路板(Printed Circuit Board,PCB)及接口电缆互连结构,在连接处产生共模电压源并激励PCB板和接口电缆构成的共模回路向外发射电磁波.通过建立理论模型,分析了键盘产生伴随电磁辐射的机理,并基于该模型对PCB板-电缆互连结构进行了定量计算及电磁全波仿真.用实验的方法在近场截获了键盘的按键信息.实验结果表明:计算机键盘伴随产生的电磁骚扰噪声中含有按键信息并可在近场被截获.     

基于GPS循环平稳特性的盲波束形成算法改进

在卫星导航自适应阵列抗干扰中,为避免先验信息误差和阵列误差对自适应波束形成性能的影响,可采用基于正交投影和导航信号循环平稳特性的盲波束形成算法(OCAB)。针对GPS信号,采用周期延迟信号处理的OCAB算法(CDOCAB)时,由于数据长度有限,噪声循环自相关函数估计量不为零,因此将影响循环平稳方法的性能,而采用解重扩数据辅助的OCAB算法(DS-OCAB)可以避免噪声估计误差的影响。将两种算法进行仿真比较,仿真结果表明,DS-OCAB算法可在少数据量的情况下保证算法性能不下降,提高算法的稳健性。     

Phase-sensitive manipulation of squeezed state by a degenerate optical parametric amplifier inside coupled optical resonators

rency-like (EIT-like) effect and the optical parameter conversion process at the same time in one optical device. These properties can favor higher manipulation precision and control efficiency, which is more suitable for the integration of quantum-on-chip systems, laying a foundation for the practical application of quantum information.     

Tunnel visible light communication system utilizing frequency domain pre-equalization technique

Simultaneously improving the communication speed and equalizing the nonlinear frequency response are still challenging for tunnel visible light communication(TVLC) system. Here, we propose and numerically investigate a frequency domain pre-equalization scheme for discrete multitone(DMT) modulation TVLC system. The amplitude of each subscriber is appropriately pre-equalized by optimized nonlinear compensation parameters. Simulation results demonstrate that our proposed equalization technique can ...     

用于超外差接收机提供本振源的高功率510 GHz单片集成三倍频器

本文介绍了一种基于砷化镓材料的高功率490~530 GHz单片集成三倍频器。基于提出的对称平衡结构,该三倍频器不仅可以实现良好的振幅和相位平衡,用来实现高效的功率合成,还可以在没有任何旁路电容的情况下提供直流偏置路径以保证高效倍频效率。同时,开展容差性仿真分析二极管关键电气参数与结构参数对倍频性能的影响研究,以便最大化提升倍频性能。最终,在大约80~200 mW的输入功率驱动下,研制的510 GHz三倍频,在490~530 GHz频率范围内,输出功率为4~16 mW,其中峰值倍频效率11%。在522 GHz频点处,该三倍频在218 mW的输入功率驱动下,产生16 mW的最大输出功率。该三倍频器后期将用于1 THz的固态外超外差混频器的本振源。     

一种便携式外场用MRTD测试仪的研制

目前热像仪MRTD测试主要在室内,为了满足外场热像仪MRTD测试的需求,研制了一种便携式MRTD测试仪.文章主要阐述了仪器的研制原理、光学优化设计、结构设计及黑体组件等的设计要点.目前,该仪器已经用于外场环境的热像仪MRTD测试,结果准确.     

亮度增益对基于像增强器的目标背景对比度影响

亮度增益为微光像增强器的重要参数,影响微光夜视环境下以微光像增强器为核心的目标背景对比度测试结果精度.本文基于对比度测试原理,通过对不同亮度增益的ICCD进行目标背景对比度测试,分析得到亮度增益与目标背景对比度的变化关系及影响因素.测试结果表明:亮度增益分别为12000 cd/(m2·lx)、8300 cd/(m2·l...     

First-principle study of ferroelectricity in PbTiO3/SrTiO3 superlattices

We performed the first-principles calculation to investigate the electronic structure and polarization behaviors in PbTiO₃/SrTiO₃ (PST) superlattices. The DOS (density of state) profiles show that there are strong hybridizations of atom Ti–O and Pb–O which play very important roles on ferroelectricity of the PbTiO₃/SrTiO₃ superlattices. Comparing to the corresponding paraelectric phase, we find the electrons of the PT (PbTiO₃) layers occupy lower energy states and electrons of the ST (SrTiO₃) layer occupy higher energy states. It is shown that the polarizations of the superlattices decrease with proportion of SrTiO₃ increasing. The constant polarization of local layer indicates that PST superlattices with small modulation lengthen can be approximately considered as a single ferroelectric material. Furthermore, according to electrostatic model, we find that directions of internal electric fields in PT and ST layers are opposite. In PST superlattices, internal electric field in PT layer leads to the loss of polarization of this layer, but the polarization of ST layer is induced by internal electric field of this layer. Compared to the value of the polarization in bulk PbTiO₃, polarization of PST is smaller.