射频已调波同步技术在单频网中的应用探讨

本文首先分析同步广播单频网的常见技术问题,阐述传统基带同步方式与射频同步方式的不同特点,随后对射频已调波技术理论做简要介绍,最后对基于射频已调波方式的同步广播单频组网方法进行探讨.     

Terahertz Photonics: Optoelectronic Techniques for Generation and Detection of Terahertz Waves

Optoelectronic techniques for generation and detection of terahertz (THz) signals have been reviewed. The operation principles of THz photomixer sources and THz parametric sources have been studied and recent developments in these areas have been presented. The performances of developed THz optoelectronic sources have been discussed and compared.      

Terahertz Emission in Asymmetric Quantum Wells by Frequency Mixing of Midinfrared Waves

Generation of terahertz (THz), and sub-THz, coherent waves has been demonstrated at room temperature in GaAs-AlGaAs asymmetric quantum wells by mixing two CO₂ laser beams. Two overlapping regimes were studied: the double resonance regime where three states are involved and the optical rectification which relies on two states only. The measured conversion efficiency of ~10^-7 W^-1 is in reasonable agreement with theoretical predictions. In addition, this technique of THz generation provides a model system to study the emission profile from an ensemble of radiating dipoles. For instance, backward emission and strong diffraction effects have been observed     

Terahertz Frequency Combs

We review recent work on THz frequency combs generated by femtosecond lasers. An overview about the underlying theory and application examples for the analysis of THz signals are given. Using different optoelectronic detection methods, spatially resolved measurements of frequency, phase, and amplitude of GHz and THz emitters are presented. The measurement setup allows for high-precision measurements of the frequency (accuracy of 9 · 10^{? 14}within a 10 s measurement interval), relative amplitude (standard deviation of the mean 0.1 %) and phase (standard deviation of the mean 0.2°). Moreover, the accuracy and invasiveness of different optoelectronic techniques are compared. The large spectral coverage provided by THz frequency combs is demonstrated by simultaneously measuring signals at 16 GHz and 28 THz.     

Scattering of Terahertz Waves by Snow

Journal of Infrared, Millimeter, and Terahertz Waves - The applications of terahertz (THz) wireless communication require studies on link performance in all kinds of atmospheric conditions,...     

基于Wigner-Hough变换的线性调频信号检测性能

根据Wigner-Hough变换思想和检测理论,分析了线性调频信号的检测性能,给出了虚警概率和检测概率的数学表达式,该表达式是Hough变换的积累单元数和检测门限的函数,然后对概率密度函数进行了合理近似,并给出了Hough变换的积累单元数计算公式,最后仿真分析了基于Wigner-Hough变换对线性调频信号相干积累相对于傅立叶变换的优越性.     

Direct Measurements of Terahertz Meta-atoms with Near-Field Emission of Terahertz Waves

We present the direct measurements of terahertz meta-atoms, an elementary unit of metamaterials, by using locally generated terahertz waves in the near-field region. In contrast to a conventional far-field terahertz spectroscopy or imaging, our technique features the localized emission of coherent terahertz pulses on a sub-wavelength scale, which has a potential for visualizing details of dynamics of each meta-atom. The obtained data show the near-field coupling among the meta-atoms and the impact of the electric field distribution from the excited meta-atom to neighbor meta-atoms. The observable LC resonance response is enhanced with an increase of numbers of meta-atoms. Furthermore, our approach also has a potential for visualizing the individual mode of meta-atom at different terahertz irradiation spots. These data can help us to understand the important role of the meta-atom in metamaterials and develop the novel terahertz components and devices such as active terahertz metamaterial and compact, high-sensitive bio-sensor devices.     

基于Wigner-Hough变换的LFM信号检测性能分析

根据Wigner-Hough变换思想和广义似然比检验理论,分析了双门限情况下线性调频信号的检测性能,给出了虚警概率和检测概率的数学表达式,该表达式是Hough变换的积累单元数和检测门限的函数,然后对概率密度函数进行了合理近似,并给出了Hough变换的积累单元数计算公式,最后的计算机仿真比较了傅立叶变换和Wigner-Hough变换的LFM(Linear Frequency Modulated)信号检测性能和基于Wigner-Hough变换的不同目标起伏类型的LFM信号检测性能.     

Microstructure Functional Devices-Effectively Manipulate Terahertz Waves

Terahertz (THz) technology promises important applications including imaging, spectroscopy, and communications. However, one of limitations at present for advancing THz applications is the lack of efficient devices to manipulate THz waves. Here, our recent important progresses in THz functional devices based on artificial microstructures, such as photonic crystal, metamaterial, and plasmonic structures, have been reviewed in this paper, involving the THz modulator, isolator, and sensor. These THz microstructure functional devices exhibit great promising potential in THz application systems.     

GaAs基单电子晶体管低温探测THz光子的研究

低温条件下具有肖特基围栅结构的GaAs基单电子晶体管可重复探测到THz光子的光电流响应.实验表明,2.54THz的CH3OH气体激光垂直入射到单电子晶体管的量子点上,在随栅压变化的源漏共振电流峰附近,产生附加电流峰.通过这两个峰位的栅压间距可以估算出THz光子的能量.这表明附加电流峰是由THz光子辅助电子隧穿产生的.实验和理论都表明,单电子晶体管量子点尺寸的减小有利于THz光电流信号的增强.     

GaAs基单电子晶体管低温探测THz光子的研究

低温条件下具有肖特基围栅结构的GaAs基单电子晶体管可重复探测到THz光子的光电流响应.实验表明,2.54THz的CH3OH气体激光垂直入射到单电子晶体管的量子点上,在随栅压变化的源漏共振电流峰附近,产生附加电流峰.通过这两个峰位的栅压间距可以估算出THz光子的能量.这表明附加电流峰是由THz光子辅助电子隧穿产生的.实验和理论都表明,单电子晶体管量子点尺寸的减小有利于THz光电流信号的增强.     

单点光学终点检测系统的研究

为了使CMP抛光精度更为精确,根据光学干涉原理设计了单点光学终点检测装置,给出了整套检测系统的简图和处理流程.在理想条件下,仿真单点光学检测的相干相位及反射率迹线,得出反射率迹线与抛光掉的透明层存在着函数关系,在实际条件核实了二者之间映射情况.采用九点测量后确认此函数条件下的单点光学终点检测具备高度的精确性,在此基础上推测了抛光头吸附晶圆以设定频率摆动情况下,光学传感器采集与处理数据的方法和过程.实际工艺操作证明,在综合运动条件下,其精度也达到要求.     

步进调频宽带雷达距离扩展目标频域检测算法

论文研究高斯杂波背景下步进调频宽带雷达的距离扩展目标检测问题。根据步进调频宽带雷达目标高分辨距离像的特点,提出一种基于回波功率谱的距离扩展目标频域检测算法。该算法无需对目标抽取形成1维距离像,直接利用目标高分辨距离像功率谱与杂波功率谱的差异,在频域实现了距离扩展目标回波能量的积累。推导了算法的检验统计量,给出了虚警概率的表达式。最后通过Monte-Carlo仿真验证了算法的检测性能。仿真结果表明该文的目标检测算法较目标抽取后的检测算法在检测性能上有明显提高,同时其检测性能也优于同条件下基于视频积累的距离扩展目标检测算法,并且具有良好的鲁棒性和工程可实现性。     

欠采样与ZFFT在移频信号检测中的应用

轨道移频信号检测需要具有相对较高的频率分辨率。在检测仪器内存和FFT计算长度有限制的情况下,为进一步获得较高的频率分辨率,则需对有用频段进行选频细化分析。文中将欠采样技术与ZOOM-FFT频谱细化技术相结合,用Matlab软件,对国产18信息轨道移频信号检测算法进行仿真验证,结果表明所提出的检测算法是可行的,并为轨道电路移频信号检测仪表的设计提供了方法依据。     

Coherent Generation and Detection of Continuous Terahertz Waves Using Two Photomixers Driven by Laser Diodes

We report on a completely coherent, tunable, continuous-wave THz system where, for the first-time, both the transmitter and receiver are log-periodic-antenna coupled LTG-GaAs based finger-photomixers. This compact room-temperature system exhibits signal-to-noise ratios (> 10³) comparable to or better than what is reported in the literature, and has potential applications in high-resolution spectroscopy and imaging. For the purpose of demonstration, we also present results of spectroscopy measurements carried out on fused silica, which are in agreement with previously published THz-TDS measurements.     

常规采样与过采样点目标检测性能比较分析

对于红外扫描有效载荷等光电探测系统,瞬时视场的减小(提高分辨率)对抑制背景杂波、提高检测概率和降低虚警率具有重要意义。过采样技术一直是提高仪器成像分辨率时的研究热点。针对点目标探测系统,对常规采样和过采样两种采样体制进行了对比分析。结果表明,在响应的标准差、平均响应和超出率方面,过采样系统具有明显优势。     

基于帧格式的调频遥测信号检测方法分析

针对航天器测控特点,低信噪比信号检测是实现航天测控系统目标快速捕获的关键技术。为了解决调频遥测信号低信噪比检测难题,介绍了采用正交矢量瞬时测频方法的调频遥测信号解调方法,分析了调频遥测信号帧格式,在此基础上提出了基于帧格式的调频遥测信号匹配滤波检测法。仿真结果表明所提方法能实现在低信噪比条件下调频遥测信号的高概率检测。     

Subjective Tests of a Companded, Frequency Modulated, Single Channel Per Carrier Communication System

Subjective tests were performed to evaluate components of an FM-SCPC communications system including a syllabic compandor, a VOX circuit, and a shallow emphasis network. The subjective improvements in the signal-to-noise ratio were determined for these components separately and in combination. Tests of the syllabic compandor were conducted at four talker levels and at two values ofC/kTfor the SCPC equipment. Further listening tests were conducted to evaluate the advantage produced by (a) the VOX alone, (b) the VOX operating with the compandor, and (c) the VOX, compandor and a shallow emphasis network. Group distributions of compandor advantages are presented for use in designing SCPC systems.     

高阶QAM调制下OFDM的载波与采样频偏联合纠正

采用高阶QAM (Quadrature Amplitude Modulation)调制的正交频分复用(OFDM,Orthogonal Frequency-Division Multiplexing)系统,相对于低阶调制来说,密集的星座点分布更容易受到载波频偏与采样频偏的影响.本文分析了高阶QAM OFDM系统对频率同步精度的要求,提出了一种载波与采样频偏联合纠正的方法,并分别针对时不变多径信道和块衰落多径Rician信道给出了频偏估计的均方误差解析表达式.均方误差的理论分析与计算机仿真结果吻合;误比特率性能仿真表明,频偏纠正后的误比特率性能与无频偏情况比较,差异小于1dB.     

利用谐振原理进行单频点检测及频谱分析

在使用FFT进行频谱分析的时候，自身的一些缺点难以克服。由于谐振器件有着一些优良的特性，本文尝试用谐振原理进行单频点检测及频谱分析，推导出谐振子的设计和仿真公式。并用实验进行了验证，初步论证了其可行性。